inborn errors of metabolism_feb2011
TRANSCRIPT
“The central idea of early disease detection and treatment is
essentially simple. However the path to its successful achievement
(on the one hand, bringing to treatment those with previously
undetected disease and, on the other, avoiding harm to those
persons not in need of treatment) is far from simple though
sometimes it may appear deceptively easy.”
Wilson and Jungner, 1968, WHO
Box 1
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Newborn screening forinborn errors of metabolism:principles, policies andweighing the evidenceJ V Leonard
C Dezateux
AbstractNewborn screening for metabolic disorders has become a contentious
issue. The aim of screening is to identify individuals at risk and start treat-
ment before they become ill. To this end newborn screening programmes
are well established in many countries and recent technological develop-
ments have lead to an expansion of these programmes. These require care-
ful evaluation, both of the process and the outcome. The original Wilson
and Jungner criteria for evaluation are still valid but, in this review, three
main points are particularly considered. The burden and the natural history
of the disease need to be defined. The test should predict accurately those
who would develop clinical disease but current screening programmes
detect many with ‘mild’ disease, the importance of which is often unclear.
This is particularly relevant when assessing any improvement in outcome
which should be seen in terms of the advantages and problems for both
the individual and the family.
Keywords genetic testing; healthcare evaluation mechanisms; health
policy; high-throughput screening assays; infant, newborn; mass
screening; metabolism, inborn errors; Neonatal screening; public health
practice; tandem mass spectrometry
Introduction
Newborn screening for inborn errors of metabolism is now well
established in developed countries worldwide. As noted byWilson
and Jungner in their 1968 WHO report on the Principles and
Practice of Screening for Disease (Box 1), screening seems both
intuitive and attractive: it aims to detect and manage serious
diseases in order to secure an outcome better than that which
might be achieved following clinical presentation or diagnosis.
The recognition that presymptomatic diagnosis and treatment
could profoundly alter the outcome for phenylketonuria (PKU)
drove Guthrie to develop a screening test based on dried blood
spots that was cheap and feasible for mass screening of newborn
infants. Screening for PKU was first introduced in the 1960s and
was followed, in the 1970s, by screening for congenital
J V Leonard PhD FRCP FRCPCH is Professor Emeritus at UCL Institute of Child
Health, 30 Guilford Street, London WC1 1EH, UK.
C Dezateux MD FMedSci is Professor of Paediatric Epidemiology and
Director of MRC Centre of Epidemiology for Child Health, London, UK.
PAEDIATRICS AND CHILD HEALTH 21:2 56
hypothyroidism. Newborn screening programmes for these two
disorders are now almost universal in high- and middle-income
countries throughout the world. While regarded as examples of
effective preventive medicine, almost half a century later expe-
rience with newborn screening for these conditions exemplifies
some of the difficulties in establishing that all those identified
and treated as a consequence of screening do in fact need treat-
ment, and the nature of the benefit conferred.
More recently there has been a marked expansion of newborn
screening programmes, driven by the development of technolo-
gies adaptable for high through-put analyses of biomarkers in
newborn dried blood spots, notably tandem mass spectrometry
(MS-MS). It is likely that future expansion will be driven by the
development of new treatments for rare disorders or by new
approaches to identify risk for or susceptibility to more complex
or chronic diseases, as much as by new technologies. Currently
parents of newborns in many countries are now offered testing
for more than 30 disorders, many of them very rare. However,
not all countries have implemented ‘expanded’ newborn
screening on this scale, reflecting different screening policies and
approaches to their evaluation.
In this contribution, we review the criteria by which proposed
screening programmes are assessed and discuss aspects that are
specific to the assessment of newborn screening for rare condi-
tions such as inborn errors of metabolism. We highlight some of
the challenges in obtaining and evaluating the evidence needed
to inform screening policies for these conditions. Detailed infor-
mation about screening for specific disorders is covered by other
contributors to this mini-symposium.
Definition of screening
Wald defined screening as the ‘systematic application of a test or
enquiry to identify individuals at sufficient risk of a specific
disorder to warrant further investigation or direct preventive
action, amongst persons who have not sought medical attention
on account of symptoms of that disorder.’ [Wald N. Guidance on
terminology. J Med Screening 1994; 1(1): 76].
While the rationale for screening is driven primarily by
concern to improve outcome for affected individuals, in this
definition, Wald reminds us that all those offered screening do
not usually have any concerns or symptoms related to that
condition that has so far prompted them to seek medical care. In
doing so, he highlights an implicit and ethical imperative to do
no harm to those screened. The implication is that the potential
benefits of screening should be positively balanced in relation to
potential harms. This requires a judgement based on a range of
complex and often imperfect information.
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SYMPOSIUM: INBORN ERRORS OF METABOLISM
Approaches to evaluating screening programmes
In their original WHO publication, Wilson and Jungner distin-
guished the evaluation of screening procedures from the evaluation
of effects of screening (namely reduced morbidity and mortality).
Newborn screening as a process, not just a test: the various stages in
this process require careful assessment to ensure that the perceived
advantages are genuine and outweigh any potential harm. While
most would agree that there need to be demonstrable benefits to
screening, views vary regarding the types of benefits to be consid-
ered, the weighting given to those benefits, and the evidence of
benefit which is needed before screening policy can be made and
programmes implemented. For example, some argue that early
diagnosis per se is a legitimate goal of screening, irrespective of
evidence of improved health outcomes.
Wilson and Jungner were the first to outline a broad and
systematic approach to evaluation and in their original report
identified 10 major criteria which needed to be addressed (see
Box 2). In the United Kingdom these criteria have been extended
into a framework comprising 22 criteria which are used for the
evaluation of all screening programmes by a National Screening
Committee. In certain countries, specific policies have been pub-
lished about newborn blood spot screening, for example, by the
Human Genetics Society of Australasia or the American College of
Medical Genetics. All these frameworks have common elements
and there is broad consensus that decisions should be informed by
the evaluation of scientific evidence. In this article we have iden-
tified three main areas for evaluation, summarized as (1) the
burden of the disease for which screening is being offered; (2) the
clinical validity of the screening test and (3) the clinical utility of
the screening programme. Belowwe discuss these in the context of
newborn screening for inborn errors of metabolism and highlight
some specific challenges in programmes for rare diseases. We
conclude by considering some additional issues related to rare
The Wilson and Jungner criteria for evaluatingscreening programmes
1 The condition sought should be an important health problem.
2 There should be an accepted treatment for patients with
recognized disease.
3 Facilities for diagnosis and treatment should be available.
4 There should be a recognizable latent or early symptomatic
stage.
5 There should be a suitable test or examination.
6 The test should be acceptable to the population.
7 The natural history of the condition, including development
from latent to declared disease, should be adequately
understood.
8 There should be an agreed policy on whom to treat as patients.
9 The total cost of case finding (including diagnosis and treat-
ment of patients diagnosed) should be economically balanced
in relation to possible expenditure on medical care as a whole.
10 Case finding should be a continuous process, not a “once
and for all” project.
Wilson and Jungner, 1968, WHO
Box 2
PAEDIATRICS AND CHILD HEALTH 21:2 57
diseases, drawing on the UK National Institute for Health and
Clinical Excellence (NICE) guidance on the principles to be used
when applying social value judgements to policy evaluations and
guidance.
Epidemiological considerations: the burden of disease
The importance of a condition for which screening is offered
relates not just to its frequency but also to its consequences.
Wilson and Jungner noted that ‘phenylketonuria is extremely
uncommon but warrants screening on account of the very serious
consequences if not discovered and treated very early in life.’
A rare disease has been defined as a condition which affects
less than five people in 10,000: by this definition almost all inborn
errors of metabolism are rare. Many are, in fact, very rare which
pose problems in acquiring reliable and unbiased information
about their frequency, natural history, clinical outcome and the
effects of treatment. In the UK all paediatricians contribute to the
surveillance of rare diseases through a monthly active reporting
scheme run by the British Paediatric Surveillance Unit. This has
proved a valuable mechanism for studying the epidemiology and
early clinical course of a wide range of candidate conditions for
newborn screening, including galactosaemia, medium chain acyl
CoA dehydrogenase deficiency (MCADD), glutaric aciduria type 1
and congenital adrenal hyperplasia. This scheme can also be used
to obtain useful information about the burden of clinically pre-
senting and diagnosed disease and importantly helps to identify
whether there is a window of opportunity for screening to make
a difference, referred to by Wilson and Jungner as a latent or early
symptomatic phase which allows time for diagnosis and initiation
of definitive treatment and management.
While the natural history of those with severe disease may be
well documented, the course of those with ‘mild’ disease may
not: such individuals may present infrequently to a clinician or
may not be ascertained at all clinically but are nevertheless
identified by screening. The problems associated with the wide
range of the clinical phenotype are discussed later.
Surveillance studies of rare diseases may also provide infor-
mation about their geographical variation, but this is not usually
helpful in determining whether screening should be offered to
geographically defined populations. It can in practice be difficult to
determine whether an apparent geographical cluster of a rare
disease ascertained by active surveillance relates to a true differ-
ence in its frequency, to differential ascertainment or reporting, or
to availability of specialist services and referral patterns. While
targeting higher risk populations that may be geographically iso-
lated or separated by custom or religion is an attractive proposi-
tion, this presupposes a robust strategy for selecting those at
higher risk. For example, although tyrosinaemia type 1 was
recognized to be more prevalent in one area of Quebec e Sague-
nay-Lac St Jean e in practice screening is offered throughout the
province. Similarly where the risk of a rare disease is higher in
certain ethnic groups it may appear attractive to consider using
ethnicity as a basis for offering screening. However the difficulties
of ascertaining ethnic origin in contemporary populations with
high rates of migration and inter-ethnic union make such selection
unreliable, as has been demonstrated by the progressive aban-
donment of ‘selective’ newborn screening strategies for sickle cell
disorders in the United States.
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SYMPOSIUM: INBORN ERRORS OF METABOLISM
These epidemiological considerations remain important when
considering the scientific rationale for screening policies that
utilize one technology for multiplex testing such as tandem mass
spectrometry: the addition of any individual disorder to
a screening panel requires careful appraisal of disease burden
and the likely health gain for those affected.
Evaluating the screening procedure: clinical validity
Conventionally we think of a screening procedure as discrimi-
nating those with a condition from those without, however
technological developments in presymptomatic diagnosis are
such that a broader phenotype than that which presents clinically
is detected which challenges pre-existing definitions and
concepts of disease. Clinical validity refers to the accuracy with
which a screening test can predict the presence or absence of
latent clinical disease, principally a clinical relevant phenotype
that provides the rationale for screening.
By definition, screening tests are not diagnostic tests. So
screening implies the need for further assessment by a diagnostic
test or tests to be offered to those above a predefined threshold
on that screening test in order to separate reliably those with
a specific condition from those without. This threshold is usually
set to optimize detection of affected individuals while avoiding
falsely labelling health individuals who may be worried unnec-
essarily or be exposed to the risks of subsequent diagnostic tests.
The specific threshold is informed by the biomarker distribution
in the normal population, the analytic validity (accuracy and
reliability) of the test, the aims of screening and the drawbacks of
an inaccurate positive or negative result. Data from screening
large population samples using standardized protocols are
needed to evaluate proposed newborn screening procedures for
rare diseases.
A diagnostic test is essential in order to provide those tested, or
their parents, with confirmation of diagnosis and information
about prognosis and future management. It is also essential in
order to evaluate the screening procedure, the effects of screening
in terms of reduced morbidity and mortality of those affected by
the target condition, or the unintended identification of other
conditions and their significance. Readers will be familiar with the
conventional measures used when evaluating screening proce-
dures (detection rate, false positive rate and predictive value).
Although simple to compute, collection of such information for
rare diseases poses specific challenges.
The first challenge is the need for an agreed method to define
who is affected: this requires case definitions and diagnostic
criteria that work in the absence of clinical symptoms, as the
majority of newdiagnoseswill be identified through screening and
will, by definition, be presymptomatic. Specifying ‘gold standard’
diagnostic tests and their interpretation can be challenging where
a state of the art diagnostic technology, such as tandem mass
spectrometry, is also used for newborn screening and where
clinicians have historically interpreted biochemical findings in the
context of the presenting clinical features.
The second relates to the need to ascertain all those ever
diagnosed with the condition, irrespective of whether this has
been through screening or clinical presentation. Underascertain-
ment of those ‘missed’ by screening (false negatives) will, by
definition, overestimate the detection rate or sensitivity of a test.
PAEDIATRICS AND CHILD HEALTH 21:2 58
The precise approach to ascertaining diagnoses will depend on the
natural history of the condition (determining the duration of
follow up of a screened birth cohort), the likelihood of clinical
diagnosis in death or life (reflecting access to specialist diagnostic
services), as well as the availability of surveillance systems to
obtain and collate reports and data. For rare diseases, data are
needed at a national level, but for very rare diseases, international
collaboration may be needed in order to derive sufficiently precise
estimates.
The third challenge lies in relating the screening phenotype to
the clinical phenotype. It is well recognized that the frequency of
a rare disease rises following the introduction of screening,
reflecting the identification of individuals who might never have
developed symptoms or adverse outcomes from their disease
(milder phenotypes). It may not be possible, on the basis of tests
carried out on newborns, to differentiate those with milder
phenotypes from those likely to present clinically and hence to
determine whom to treat. This oftenmeans that all or most of those
detected by screening are treated. As a consequence it can be
difficult to be sure these are all ‘true’ cases (in the sense of having
the clinically relevant phenotype), to calculate screening test
performance (detection and false positive rates) and to characterize
the benefits of screening (in terms of reduced morbidity and
mortality).
Evaluating the effects of screening: clinical utility
Clinical utility refers to the likelihood that screening will lead to
an improved outcome for the affected individual and their family.
Conventionally interest has focused on health outcomes, princi-
pally mortality and morbidity. While these are crucial there is
increasing recognition of the importance attached by affected
individuals and their families to other health outcomes, including
patient reported outcome measures: these may include measures
of quality of life, broad aspects of cognition, intellectual and
emotional development, adult health including future reproduc-
tive potential, and so on. All reflect a wider view and concept of
benefit. Grosse and Khoury reviewing the concept of clinical
utility in relation to genetic testing note the shift to a broader
perception of benefits in debates around expanded newborn
screening, including reduction in the ‘diagnostic odyssey’, the
right to diagnosis even in the absence of effective treatments, and
future reproductive choices (for the parents) in the case of
inherited disorders. Hence it is important to consider and agree
the outcomes which screening seeks to improve and to define the
objectives of screening in relation to these outcomes. Whatever
the outcomes selected, Grosse and Khoury emphasize the
importance of using objective measures for the assessment.
As diagnosis alone will not achieve better health outcomes,
the clinical utility of screening will also depend on the avail-
ability of effective treatments or other interventions. This in turn
depends on evidence about two distinct aspects of effectiveness:
firstly, whether treatment improves the specific outcomes of
interest and secondly whether treatment following screening, i.e.
before symptoms are evident, results in a greater improvement in
outcome than achieved when treatment is given following clin-
ical diagnosis. Unfortunately in the case of most inborn errors of
metabolism, such evidence is rarely obtained from clinical trials,
rarely pertains to the range of outcomes of interest or to the
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SYMPOSIUM: INBORN ERRORS OF METABOLISM
duration of follow up needed to assess them fully. Observational
studies of screening often rely on comparison with the outcome
of children diagnosed in the past before screening started or
contemporaneously following clinical diagnosis in an area where
screening is not offered. Neither is ideal since outcome may be
confounded with differences in access to other treatments or to
overall management and healthcare. Wilcken has argued that the
lack of evidence on outcome should not delay the introduction of
screening e this argument has proved persuasive in the United
States but less so in the United Kingdom. She has at the same
time highlighted the paucity of data on longer-term outcome and
the need to collect it and the challenges in doing so for very rare
conditions. One implication of this is the need to collect outcome
data following implementation.
Finally, assessments of utility also need to incorporate the
disbenefits, real and perceived, of screening in order to ensure
that overall there is more harm than good. This can be very
challenging since the majority of those tested will not have the
condition of interest and may have concerns relating to the
potential for misdiagnosis, medicalization, stigma and anxiety,
however transient, which need to be respected. As with benefits,
evidence of disbenefits e objectively measured e is needed and
is often lacking.
Generating and weighing evidence: effectiveness, cost
effectiveness, social values
We have outlined the most common elements of the frameworks
used in many countries to assess whether a new screening pro-
gramme should be introduced. Such assessments should be
based on high quality, objective and scientifically rigorous
information on a range of benefits and disbenefits relevant to the
goals of screening, which can be objectively measured. We have
identified some of the challenges in acquiring such information,
especially for rare disorders such as many inborn errors of
metabolism. Policy makers typically need to consider not only
the benefits and disbenefits but also the value for money and
opportunity costs of deploying limited healthcare resources into
a new screening programme. Health economists help to make
these decisions more rationally based by using formal methods of
combining evidence and its uncertainty in cost effectiveness
analyses that incorporate multiparameter evidence synthesis.
This allows the costs and effects of different policy options to be
compared and may provide conclusive support for one particular
option.
Such decisions need also to take account of wider social values
and the ethical principles which underlie decisions on healthcare.
These have been clearly summarized in a very useful document
produced by the UK National Institute of Health and Clinical
Excellence which sets out some of the procedural and bioethical
principles to be considered in developing guidance and policies
formulated and developed following wide public consultation. The
processes which lead to guidance or policy should be scientifically
rigorous, including all parties with a legitimate interest in the
guidance under consideration, be transparent, independent, open
to challenge and timely. The ethical and moral principles which
underpin clinical and public health practice include respect for
autonomy, non-maleficence, beneficence and distributive justice
or fairness and these need to be considered when making
PAEDIATRICS AND CHILD HEALTH 21:2 59
judgements about effectiveness, cost effectiveness and allocation
of resources. NICE highlights the importance of developing
evidence-based guidance recognizing that recommendations
should not be made where evidence is too weak to permit
reasonable conclusions to be drawn. Where there is a lack of
evidence of effectiveness more research is needed and it is
important that there is a mechanism for funding such research
based, if necessary, on large-scale pilot studies.
Public involvement and informed choices
Implicit in much of our discussion about outcomes and social
values is the need for scientists and clinicians to work in part-
nership with parents and the public in order to develop guidance
and policies and then to implement them. The rapid expansion in
screening programmes in the United States, driven in part by
advocacy from groups representing families affected by specific
rare conditions, now means that the parents of a new baby are
being asked to consent to testing of up to 30 conditions. This
poses challenges in obtaining informed consent. Qualitative
research suggests that relative ineffectiveness of some treatment
may moderate parental enthusiasm for some tests and more
work is needed if we are to implement programmes that respect
autonomy of child and parent in their decision making in
a meaningful way.
Summary
We have set out a broad framework which we believe should be
employed for the evaluation of proposed newborn screening
programmes, elaborating some challenges which apply when
considering rare inborn errors of metabolism. It is essential to
establish the goals and outcomes of screening for each condition
and then to appraise the evidence for disease burden, clinical
validity and clinical utility. In weighing this evidence a set of
procedural and ethical principles can be applied in order to make
difficult decisions in the best way possible.
Role of the funding source
James Leonard is retired and has no sources of funding.
Carol Dezateux is employed by University College London. Her
post is funded by the Higher Education Funding Council of
England (HEFCE) and the Department of Health. Work carried
out at the MRC Centre of Epidemiology for Child Health benefits
from funding from the Medical Research Council (G0400546).
None of these sponsors had any role in the writing of this
manuscript.
Conflict of interest
James Leonard is chairman of the Diagnostic Review Panel of the
UK Collaborative Study of Newborn Screening for MCADD. He
has chaired and received payment for a workshop funded by
Swedish Orphan on newborn screening for Tyrosinaemia type 1
(fumarylacetoacetase deficiency).
Carol Dezateux is Strategic Director of the UK Newborn
Screening Programme Centre which is funded by the UK Depart-
ment of Health but has contributed to this article in a personal
capacity. She is principal investigator of the UKCollaborative Study
of Newborn Screening for MCADD which is funded by the UK
� 2010 Elsevier Ltd. All rights reserved.
Practice points
C Newborn screening programmes for inborn errors of meta-
bolism should be evaluated using recognized frameworks.
C It is essential to establish the goals and outcomes of
screening for each disorder.
C Screening policy requires evidence on the burden of the
disorder for which screening is being offered, the clinical
validity of the test and the outcome.
C For rare diseases, systematic strategies to evaluate longer-
term outcomes are needed in order to evaluate benefits of
screening.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Department of Health. The opinions expressed here are her own
and she has no conflicts of interest to declare. A
FURTHER READING
ACMG Newborn Screening Expert Group. Newborn screening panel and
system. Genet Med 2006; 8: 1Se252.
Grosse SD, Khoury MJ. What is the clinical utility of genetic testing? Genet
Med 2006 Jul; 8: 448e50.
Human Genetics Society of Australasia. HGSAeRACP Newborn Screening
Joint Subcommittee. Newborn blood spot screening; 2008.
National Institute For Health And Clinical Excellence. Social value judge-
ments: principles for the development of NICE guidance. 2nd Edn;
2008.
National Screening Committee. Criteria for appraising the viability, effec-
tiveness and appropriateness of a screening programme. London:
Department of Health, 2003. www.library.nhs.uk/screening (accessed
Sep 2010).
PAEDIATRICS AND CHILD HEALTH 21:2 60
Wilcken B. Expanded newborn screening: reducing harm, assessing
benefit. J Inherit Metab Dis 2010. doi:10.1007/s10545-010-9106-6.
Wilson JMG, Jungner G. Principles and practice of screening for disease.
Geneva: World Health Organization, 1968.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
PhenylketonuriaMaureen Anne Cleary
AbstractPhenylketonuria remains one of the most common inborn errors in the
United Kingdom. It is detected on the newborn heel-prick screening
sample allowing early treatment with a strict low phenylalanine diet sup-
plemented with artificial amino acids, and appropriate vitamin and
minerals. Although the long-term prognosis is good, there is an increasing
body of evidence highlighting subtle problems in neuropsychological
function with slower reaction times and poorer executive function than
peers. White matter changes clearly seen on brain magnetic resonance
imaging may have some relationship to these neuropsychological difficul-
ties but their significance is not clearly understood. The diet, although
successful, is difficult to follow lifelong and with its attendant risks of
nutritional deficiencies needs careful specialist management. In view of
these challenges new treatments such as sapropterin (a tetrahydrobiop-
terin analogue) and large neutral amino acids are currently being used
in phenylketonuria and a human trial has started using ammonia lyase
as enzyme replacement therapy. Maternal phenylketonuria syndrome
remains a risk for those who conceive whilst blood phe is elevated and
females must be counselled early in childhood to avoid this risk.
Keywords hyperphenylalaninaemia; phenylketonuria; PKU; sapropterin
therapy
Phenylketonuria (PKU) can claim at least three ‘firsts’: the first
metabolic disorder to have a successful treatment; the first to be
controlled by diet; and the first to be detected by newborn
screening. This review describes the current management and
outcome of PKU and summarizes developments of new
therapies.
Terminology
PKU was first described in 1934 by Folling as ‘imbecillitas phe-
nylpyruvica’ following the finding of phenylpyruvic acid
(a phenylketone) in the urine of two siblings with mental retar-
dation. The term phenylketonuria was later used by Penrose and
has remained the most widely used name for hyper-
phenylalaninaemia (HPA) due to phenylalanine hydroxylase
deficiency. It is now generally applied to the more severe end of
the spectrum in which phenylalanine is greater than 1200 mmol/l
whilst consuming a normal protein intake and this type is also
referred to as classical PKU. HPA is a frequently used term to
describe those with phe levels 600e1200 mmol/l on a normal
protein intake whereas levels between 120e600 mmol/l is called
mild HPA. All arise due to defects in the enzyme phenyalanine
hydroxylase (PAH); the severity relates to the nature of the
Maureen Anne Cleary MBChB MRCP MRCPCH MD is a Consultant Metabolic
Paediatrician in the Metabolic Unit, Great Ormond Street Hospital NHS
Trust, Great Ormond Street, London WC1 N 7JH, United Kingdom.
Conflict of interest: none.
PAEDIATRICS AND CHILD HEALTH 21:2 61
underlying genetic mutation. In less than 2% of cases a raised
phenylalanine (phe) level is caused by a defect in the production
or recycling of tetrahydrobiopterin (BH4). PKU is still the most
commonly used term in the United Kingdom (UK) and is used in
the remainder of this article.
Natural history
PKU causes severe intellectual impairment. In classical PKU
developmental delay is apparent within the first year of life and
progresses to severe mental retardation (IQ < 50). Examination
shows limb spasticity, tremor and microcephaly. A seizure
disorder is frequently present and EEG abnormalities are common.
Other findingsmay include hypopigmentation of the hair, skin and
iris due to reduced melanin synthesis. Parkinsonian features and
gait abnormalities are also often observed in the untreated indi-
vidual. Abnormalities of behaviour are very common including
hyperactivity, aggression, anxiety and social withdrawal. The
natural phenotype is rarely seen now due to widespread newborn
screening for this condition. However, PKU should be considered
as a possible diagnosis particularly in an individual born in
a country where newborn screening may not be available.
Detection
In most first-world countries the diagnosis of PKU is made
through newborn screening. PKU can be readily detected by
a raised phenylalanine on the newborn heel-prick blood test.
Blood phenylalanine (phe) and tyrosine (tyr) are measured. In
PKU the ratio between these two metabolites is greater than 3.
The cut-off value for a presumed positive screen varies between
countries depending on the infant’s age at screening. The UK
practice is to sample between days 5e8, using a cut-off phe of
240 mmol/l. Other causes of elevated phe, aside from PKU,
include a disorder of biopterin production or recycling, liver
dysfunction or premature babies receiving amino acid containing
parenteral feeds.
Disorders of biopterin production or recycling can cause
raised phe since tetrahydrobiopterin (BH4) is the co-factor for the
phenylalanine hydroxylase enzyme (see Figure 1). These disor-
ders, previously called ‘malignant PKU’, are best named by their
respective enzyme deficiency. In all positive screening cases
a disorder of biopterin is excluded by measuring total biopterins
and DHPR enzyme activity on blood spots. BH4 disorders result
in neurotransmitter deficiencies and individuals need replace-
ment of dopamine and 5-hydroxytrypophan in addition to BH4;
some still need dietary treatment to reduce phe levels.
Liver dysfunction can cause an elevation of phe but in these
cases other amino acids such as tyrosine, methionine and leucine/
isoleucine are also raised thus keeping the phe: tyr normal or less
than 3. Preterm babies may have raised phe levels whilst on a high
protein intake. Again, in this situation other amino acids are also
elevated making it unlikely that PKU would be missed. Preterm
babies should be tested at the same time as other newborns and
their gestation and feed content noted on the request form.
Epidemiology
The incidence of this condition in the UK is approximately 1 in
10,000 newborns. PKU is prevalent in Europe and the US. It is
� 2010 Elsevier Ltd. All rights reserved.
Pterin-4a-carbinolamine
Phenylalanine Tyrosine
PAH
q-BH2
BH4
PhenylpyruvatePhenylacetatePhenyllactate
PAH, phenylalanine hydroxylase; BH4, tetrahydrobiopterin;
q-BH2, q-dihydrobiopterin
Figure 1 The phenylalanine hydroxylation system.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
relatively common in some parts of China but is rare in African
nations. The highest incidence is observed in Turkey where the
incidence is 1 in 2600.
Biochemistry and genetics of PKU
Phenylalanine is an essential amino acid which is metabolized in
the liver by the enzyme phenylalanine hydroxylase (PAH). The
first step of catabolism of phenylalanine is irreversible conver-
sion to tyrosine. The PAH enzyme requires tetrahydrobiopterin
as its co-factor. PKU develops due to deficiency in, or absent
activity, of the PAH enzyme and results in elevated phenyalanine
and reduced levels of tyrosine. When the pathway to tyrosine is
blocked, excess phe is transaminated to phenylpyruvic acid and
excreted in urine. The enzyme is coded by the PAH gene located
on the long arm of chromosome 12. More than 400 pathological
mutations are recognized and most affected subjects are
compound heterozygotes in that they carry two different muta-
tions. There is a good correlation between pre-treatment phe
levels, phe tolerance and genotype. However, outcome is affected
by many factors and genotype knowledge is of limited value in
predicting clinical management. But mutation analysis has some
value in predicting BH4 responsiveness (see below).
PKU is inherited as an autosomal recessive condition. Prenatal
diagnosis, although rarely requested, is possible by mutation
analysis if the mutations are already identified in the index case.
Treatment
The aim of PKU treatment is the reduction of blood phe to a level
allowing normal brain development. An individual’s blood
phe depends upon dietary intake of phe and the residual activity
of phe hydroxylase. Although in some cases it is possible to
augment phe hydroxylase activity (see new treatments), in most
cases treatment relies upon reducing phe intake by a restriction of
natural protein. In most cases meat, cheese, bread, fish and milk
must be avoided. A semi-synthetic diet is used which comprises:
� foods of low phe content in unlimited amounts such as many
fruits and vegetables;
� weighed amounts of foods containing medium amounts of
phe (e.g. broccoli, potato). The amount of phe ingested is
PAEDIATRICS AND CHILD HEALTH 21:2 62
often calculated using an exchange system. In the UK system
1 ‘exchange’ ¼ 50 mg phe which is approximately 1 g protein;
� phe-free amino acid mixtures to provide normal or supra-
normal total protein intake;
� vitamins, minerals and trace elements.
The diet should be strictly followed with these food groups
evenly distributed throughout the day. Aspartame should be
avoided as it contains large amounts of phe. Infant formulae
feeds which are phe-free are available; many contain added
essential fatty acids. These are used in conjunction with a small
amount of standard infant formulae. It is possible to continue
breast feeding even in severe PKU by giving a measured amount
of phe-free formula prior to a breast feed. All PKU diets should be
administered with the advice of a specialist dietician.
Monitoring of treatment
It is vital to monitor phenylalanine levels, usually through
frequent blood spot analysis. Guidelines vary between countries
regarding frequency and acceptable phe levels. In the UK, infants
and young children should have weekly samples aiming at levels
120e360 mmol/l; school-age children fortnightly samples with
a range of 120e480 mmol/l; and in adolescents and adults
monthly samples with an upper limit of 700 mmol/l. These
guidelines are currently under review and changes can be viewed
through the UK newborn blood spot screening programme
website (see below). In addition to monitoring phe levels, other
nutritional indices such as vitamin B12, folate, iron, calcium,
phosphate and essential fatty acids should be measured in those
with poor dietary adherence. Growth parameters are also moni-
tored. Some clinics advocate regular neuropsychological testing
whereas others only refer for such assessment where difficulties
are suspected.
Nutritional issues in PKU
The nutritional sufficiency of the PKU diet must be regularly
monitored by a specialist dietician. Vitamin B12 deficiency is
a particular risk in adolescents and adults who have stopped
taking their supplements but are still restricting their protein
intake by habit. Other vitamin or mineral deficiencies have
occasionally been noted in PKU such as iron, selenium and
calcium. Bone mineral density may be lower than normal in this
group of patients although the reasons for this are unclear.
Polyunsaturated fatty acids levels are frequently low in the
plasma and red cells of PKU children on diet. This is probably
due to its low animal protein content. Although it seems prudent
to supplement PUFAs, there is not yet clear evidence on
requirements in this group nor on the long-term impact on
neurodevelopment.
Dietary adherence
Adherence to treatment in PKU is particularly challenging for
several reasons: the strict diet creates awkward social occasions;
the diet itself is unpalatable; frequent blood tests lead to needle
phobia in some children; and the diet is time consuming and may
be costly in some countries. It is important to provide education
programmes to help compliance; such as toddler groups and
teenage camps.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Duration of diet
Despite the knowledge that has accumulated on PKU, the risk of
stopping diet in adulthood is not yet known. The oldest early-
treated patients are now entering middle age. The vast majority of
these remain neurologically healthy but the possibility of late
neurological decline cannot be excluded. Current recommenda-
tion is diet for life. This is based upon the evidence of poorer
neuropsychological performancewhen phe levels are elevated and
the knowledge thatMRI of the brain shows abnormalities ofmyelin
of uncertain significance.Where diet for life is refused then at least
monitoring for life by regular clinic attendance is encouraged.
New treatments for PKU
As long-term dietary compliance is difficult there is a need for
alternative modes of treatments:
Enzyme replacement therapy
The non-mammalian enzyme phe ammonia lyase converts phe to
a non-toxic substance called transcinnamic acid. It has been
tested using enteral, intraperitoneal and subcutaneous routes.
More recently enzyme stability has been achieved by pegylation.
Plasma phe falls significantly in the mouse model experiments
and the first human trial is underway in the US.
Large neutral amino acids
The large neutral amino acids (LNAA) including phe compete at
the blood brain barrier for entry to the brain through the same
transporter (LAT1). Increasing the concentration of LNAA in the
blood therefore reduces phe entry to the brain. There is a similar
mechanism in the gut, and absorbed phe is lower if LNAA are
supplemented in generous amounts. It is unlikely that LNAA
given as sole treatment without phe restriction could replace diet
in childhood but may be a useful approach for adults.
Sapropterin therapy
BH4 therapy has been used for some time to treat defects in the
pterin pathway. However it has recently been shown that admin-
istration of BH4 can result in a reduction of phe levels even in
phenylalanine hydroxylase deficiency. The mechanisms are not
completely understood but include stabilization of residual protein
thus suggesting that thosewithmild PKU aremost likely to benefit,
however, some patients with classical PKU have also shown
a response. It is estimated that 80% of those with mild PKU and
40% of those with classical PKU will benefit from this treatment.
Genotype canhelp in predicting responsebut it cannot be assumed,
and a short therapeutic trial is required to judge BH4 responsive-
ness. Sapropterin dihydrochloride is a synthetic formulation of the
active 6R-isomerofBH4whichhasbeen licensed recently inEurope
andUS for the treatment of PKU. In Europe the license is granted for
children over 4 years of age with phenylalanine hydroxylase defi-
ciencywhohave showna response to the drug. In theUKguidelines
are needed to best define a ‘response’ to treatment in order for this
treatment to become available beyond commercial trials.
Gene therapy
The most promising results come from experiments using
recombinant adeno-associated virus vector in which long-term
correction without adverse effects has been reported in the mouse
model (PKUenu2). There are no human gene therapy studies yet.
PAEDIATRICS AND CHILD HEALTH 21:2 63
Liver transplantation
This procedure effectively provided phe hydroxylase activity in
a child with PKU who required liver transplantation for an
unrelated problem. The risks and complications of transplant
render it an unrealistic option.
Outcome of PKU
The outcome for PKU is good. If dietary treatment is started early
(before 3 weeks of age) and blood phe levels remain satisfactory,
then ultimate IQ should be in the average range although slightly
reduced in comparison with peers or siblings. After the age of 10
years IQ is stable. The small number of adolescents and adults
who have developed overt neurological disease have had poor
metabolic control in childhood. However recent research does
identify some problems in the treated PKU population.
Magnetic resonance imaging (MRI) of the brain
Brain MRI in children and adults commonly shows abnormalities
in the cerebral white matter even in treated PKU. These signal
changes are likely to be intramyelinic oedema which usually
affects the periventricular whitematter.Milder changes affect only
the occipital lobe but more severe involvement progresses
rostrally to the frontal lobe. The degree of white matter change is
associated with recent metabolic control (average phe level in the
preceding year and current phe levels) but not to early phe levels.
Despite years of investigation the functional consequences of
these findings are unclear. There is some recent evidence sug-
gesting a correlation between neuropsychological performance
and more widespread white matter changes. The MRI changes are
reversible upon lowering blood phe within about 2 months. The
lesions appear static at least over a 5-year period in adulthood if
phe levels remain stable.
Neuropsychological studies
Despite many neuropsychological studies in treated PKU it
remains difficult to draw clear conclusions: the numbers studied
are often small; the types of neuropsychological test vary
between studies; the ages are different (children or adults); the
background phe control and phe level at the time of testing vary.
The tentative conclusion is that some neuropsychological
damage occurs even in treated PKU.
Reaction times are delayed in PKU and this relates to
concurrent elevated phe levels. Executive function i.e. higher
level processes requiring interactions between several areas of
the brain, has been extensively studied as it is governed by the
pre-frontal cortex. This is a dopamine sensitive area of the brain
which may be especially vulnerable in PKU. Of the various
subsets of executive function studies, inhibitory control is
impaired in early-treated PKU. Tests of working memory may
have an age-related effect as children show largely normal results
but a decline in function is observed in adolescents and adults.
There are other behavioural and psychiatric symptoms
attributed to PKU. Poor dietary control early in life results in
anxiety, hyperactivity and social withdrawal, and those with
satisfactory early treatment still appear to have a higher risk of
low self-esteem and possibly depression. Further research is
required in this field: the size of studies must increase and their
uniformity be ensured. Longitudinal projects should also be
developed.
� 2010 Elsevier Ltd. All rights reserved.
Practice points
C PKU remains one of the most common IEM in the UK with an
incidence 1 in 10,000
C Dietary therapy remains the mainstay of treatment
C Long-term monitoring requires a specialist team in order to
avoid nutritional deficiencies
C Prognosis is good as long as phe levels are kept within
treatment guidelines
C There may be mild deficits in neuropsychological function
even in treated patients
C Treatment with sapropterin benefits some individuals with
PKU usually those with milder disease
C Enzyme replacement therapy human trials are underway.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Maternal PKU
Infants born to mothers with blood phe above 1200 mmol/l show
fetal damage including low birth weight, microcephaly, dys-
morphic facies, slow postnatal growth and development and
intellectual impairment. The facial features are similar to fetal
alcohol syndrome: small palpebral fissures, epicanthic folds, long
philtrum and thin upper lip. Although congenital heart disease is
the most common, other organ malformation can occur. The risk
to mothers with milder PKU is smaller and appears to correlate
with phe level. In view of these risks all females with PKU must
be monitored for the duration of their lives, being counselled
early in their childhood and having a longstanding trusting
relationship with their PKU team. The aim for managing
maternal PKU is for women to be on a strictly controlled diet
preconception with regular phe monitoring showing levels
between 100 and 250 mmol/l. There is also evidence that if diet is
started by 10e12 weeks of pregnancy a satisfactory outcome can
be achieved.
Summary
PKU is a success story. It can be detected early in life allowing
early instigation of dietary therapy. The treatment is effective and
children grow and develop normally. Within this framework of
success however there are still unanswered questions about
long-term neuropsychological outcome and the necessity of diet
for life. Dietary treatment remains challenging for many patients
hence the importance of the alternative approaches now on the
horizon. A
FURTHER READING
Anderson PJ, Leuzzi V. White matter pathology in phenylketonuria.
Mol Genet Metab 2010; 99(Suppl 1): S3e9.
PAEDIATRICS AND CHILD HEALTH 21:2 64
Blau N, Erlandsen H. The metabolic and molecular bases of tetrahy-
drobiopterin-responsive phenylalanine hydroxylase deficiency.
Mol Genet Metab 2004 Jun; 82: 101e11.
DeRoche K, Welsh M. Twenty-five years of research on neurocognitive
outcomes in early-treated phenylketonuria: intelligence and executive
function. Dev Neuropsychol 2008; 33: 474e504.
Feillet F, Agostoni C. Nutritional issues in treating phenylketonuria.
J Inherit Metab Dis; 2010 Feb 12 [Epub ahead of print].
Koch R. Maternal phenylketonuria: the importance of early control during
pregnancy. Arch Dis Child 2005; 90: 114e5.
MRC. Recommendations on the dietary management of phenylketonuria.
Arch Dis Child 1993; 68: 426e7.
Van Spronsen FJ. Future treatment strategies in phenylketonuria.
Mol Genet Med 2010; 99(Suppl 1): S90e5.
www.nspku.org.
www.newbornbloodspot.screening.nhs.uk.
www.bh4.org.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Galactosaemia an updateAA Broomfield
C Brain
S Grunewald
AbstractWhile galactosaemia was originally documented over 100 hundred years
ago, it still remains poorly understood and recognized. Classical galacto-
saemia is an inherited disorder of galactose metabolism, whose main die-
tary source is lactose. In the UK which does not currently screen for
Galactosaemia lack of recognition of key symptoms can lead to delays in
diagnosis. However it has become clearer that Galactosaemia is not only
an acute disease of the neonatal period but affected children potential
are prone to a number of chronic problems later in life. This review looks
at the current thinking concerning the pathogenesis and complications of
galactosaemia and summaries our current management of patients.
Keywords galactitol; galactosaemia; galactose-1-phosphate; genetic;
inherited metabolic disease; leloir pathway
Definition
The pathogenic potential of ingested galactose was originally
described over 100 years ago. It results fromadefect in the galactose
metabolic pathway, the Leloir pathway, which consists of three
enzymes, the galactose specific kinase (Galactokinase/GALK),
galactose-1-Phosphate uridyltransferase (GALT) and uridine
diphosphate galactose 40 epimerase (GALE). While a deficiency in
any of these enzymes will lead to the biochemical finding of gal-
actosaemia i.e. an elevated plasma galactose, only deficiencies in
GALT or GALE have the potential to cause the ‘classical Gal-
actosaemia’ phenotype: an acute toxicity syndrome which resolves
on removal of exogenous galactose intake with more recently
recognized long-term complications of chronic neurological, endo-
crine, and orthopaedic problems. The outcome of these chronic
problems seems to be far less tightly linked to galactose intake.
Incidence/epidemiology
The overall incidence of classical galactosaemia, secondary to
GALT deficiency, is estimated at between 1: 23,500 and 1: 44,000
Abbreviations: GALE, Galactose 40 epimerase; GALK, Galactokinase;
GALT, Galactose-1-Phophate uridyltransferase (Gal-1-Put); GALK Gal-
actokinase, GALE Galactose 40epimerase; GAL-1-P, Galactose-1-Phopshate.
AA Broomfield MSC is a Specialist Registrar in the Metabolic Medicine
Unit, Great Ormond Street Hospital for Children, London WC1N 3JH, UK.
C Brain MD is a Consultant Paediatric Endocrinologist in the Endocrine,
Department of Great Ormond Street Hospital for Children, London
WC1N 3JH, UK.
S Grunewald PhD is a Consultant in Paediatric Metabolism in the
Metabolic Medicine Unit, Great Ormond Street Hospital for Children,
London WC1N 3JH, UK.
PAEDIATRICS AND CHILD HEALTH 21:2 65
in the UK. This is in keeping with most of Western Europe,
however the incidence in different subpopulations varies greatly.
This is especially true in Ireland, where the incidence in the
travelling population is one in 450 live births whilst the overall
incidence is nearer to 1: 20,000. Worldwide the incidence does
appear to be lower than in Western Europe, being quoted as one
in 50,000 in the USA and as little as one in 100,000 in Japan.
The mild asymptomatic phenotype of GALE is relatively
common, with a frequency of 1: 6,200 in the African American
population, but the severe “generalized” presentation of GALE,
whose presentation is similar to that of classical galactosaemia is
limited to a few case studies worldwide. The GALK deficiency is
rare <1/100,000.
Genetics
The GALT gene is located on chromosome 9p13 and consists of
11 exons. Over 230 mutations have been described. The most
frequent mutation in the Caucasian population, with an overall
frequency of 65% (96% in the Irish population), is the Q188R
mutation, which results in a complete loss of enzymic activity.
The second commonest European mutation is the K285N,
a missense mutation, which predominates in central European
counties. This also results in a complete lack of GALT activity.
In contrast, S135L, which accounts for 50% of mutate alleles in
African Americans, shows near normal activity in mouse models.
Whilst there is a relatively good correlation between genotype
and residual enzymic function, the correlation between genotype
and clinical phenotype is more enigmatic, though Q188R is
predicative of a poorer clinical outcome, whereas S135L is
associated with the milder phenotype seen in Afro-Caribbean
patients.
The N314D mutation (c. 940A>G), so called Duarte variant,
can exist in two different forms: Duarte-1 and Duarte-2 has
a good clinical outcome. The Duarte-2 mutation is interesting, as
compound heterozygotes for the Duarte-2 variant and classical
galactosaemia, typically manifest 14e25% of normal GALT
activity resulting in some protection against severe toxicity.
Pathology
The exact mechanisms underlying the pathophysiology of clas-
sical galactosaemia is still not fully understood with the lack of
a good animal model hampering research; the GALT mouse
knockouts, having few of the clinical features found in humans.
However, the potential mechanisms can be grouped into,
primary effects which include the buildup of toxic metabolites
and the reduction in end products of the Leloir pathway and
secondary effects due to disruption of other interlinked
pathways.
With any disruption of the Leloir pathway, there is the
potential for excess galactose accumulation, which if uncon-
trolled will also result in accumulation of Galactitol and Gal-
actonate. These are formed due to the actions of the alternative
pathways of galactose metabolism i.e. aldase reductase and the
pentose phosphate pathway respectively (Figure 1).
Given that the GALK deficient patients do not manifest either
the acute toxicity, or any of the chronic manifestations seen in
GALT patients, it seems likely that Galactose-1-P which is absent
in GALK but present in GALT, plays a major role in their
� 2010 Elsevier Ltd. All rights reserved.
Lactose
Galactose
GALK
GALE
GALT
Galactose 1-P
UDP Galactose UDP-Glucose
UDP-Glucose
Glucose 1-P
Glucose 1-P
Glucose 6-P
Glucose
1
2
3
Galactonate
Aldose
Pentose phosphate pathwayreductase
Galactitol
Figure 1 The Leloir pathway and alternative pathways for galactose
metabolism (dotted lines). 1 ¼ hexokinase, 2 ¼ phosphoglucomutase,
3 ¼ UDP-glucose pyrophosphorylase.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
pathogenesis. The actions of GAL-1-P need further elucidation
with a variety of effects being seen, for a more comprehensive
review see Lia 2009. Recently there has been some speculation
that GAL-1-P toxic effects may be mediated via the human
tumour suppressor gene aplysia ras homolog I (ARHI), which,
since it is absent in mice, may also explain the clinical difference
seen in the mouse model. The accumulation of galactitol is
thought to be responsible for the cataracts seen, though whether
this is due to direct osmotic effects or due to oxidative damage
secondary to NADPH depletion is unclear. It is also unclear if
galactonate, cleared by the pentose 5 phosphate pathway,
contributes to the overall toxicity.
In terms of reduction of end product, the interplay of the
enzymes involved in the Leloir pathway ultimately controls the
levels of UDP-galactose, the galactosyl donor in cellular glyco-
protein/glycolipid biosynthesis. This potentially leads to abnor-
malities in post translational protein modification and abnormal
glycosylation has been demonstrated with abnormalities seen in
FSH and transferrin changes similar to those seen in congenital
disorders of glycosylation (CDG).
The most apparent affect on a secondary pathway, is the
reduction in levels of cellular inositol, with reductions in myo-
inositol being documented in vivo. GAL-1P competitively inhibits
human inositol monophosphatase and in the yeast model,
galactose toxicity can be overcome by over-expression of inositol
monophosphatase. The reduction in inositol might partially
explain the neurological symptoms seen in galactosaemic
patients since inositol is required for the formation of the
neuronal modulator Phosphatidylinositol bisphosphate.
PAEDIATRICS AND CHILD HEALTH 21:2 66
The clinical symptoms of acute toxicity syndrome of classical
galactosaemia
The natural history of classical galactosaemia is of an early onset,
potentially life threatening acute toxicity syndrome, occurring
after several days of exposure to dietary galactose from milk.
However liver dysfunction has been described as early as day 1
and milder phenotypes presenting at several weeks of age are
seen. Overall, in 266 out of 336 cases (79%) in one study, acute
symptoms were reported within 2 months of birth.
Initial symptoms are non specific with affected neonates
presenting with vomiting, diarrhoea, lethargy, hypotonia or poor
feeding with resultant poor weight gain. Given the limited
neonatal repertoire of response to illness, this is easily confused
with sepsis, a situation complicated further by the apparent
susceptibility of galactosaemics to Escherichia coli. sepsis.
Examination on presentation may reveal signs of liver
impairment such as jaundice, hepatomegaly and signs of
abnormal bleeding; as well as occasional fullness of the anterior
fontanelle either due to sepsis or pseudotumour cereberi. While
cataracts are a recognized feature of GALT deficiency they are
infrequent with only 14% of patients affected in one series with
only 20% of these presenting in the neonate period. Even when
present, they may require the use of a slit lamp for visualization.
Cataracts are the only complication in GALK deficiency,
though very rarely pseudotumour cereberi has also been repor-
ted. GALE presentation falls on a spectrum varying from isolated
hyperglactosaemia, to the severe classical galactosaemia type
picture. While there are reports of motor and intellectual delays
in the more severely affected, given the extremely small number
of reported patients and the parental cosanguineouity it is diffi-
cult to be sure these are truly features of the GALE deficiency.
Investigations
As discussed above the affected glactosaemic baby will classi-
cally present with differing severity of liver dysfunction. Table 1
gives a list of investigations that covers the common causes of
neonatal hepatic dysfunction, while Table 2 gives the specific
tests, both screening and confirmatory for galactosaemia.
The diagnosis of GALT deficiency can be confirmed by
measuring the GAL-1-PUT activity using either the Beutler fluo-
rescent spot test or an actual quantitative assay of red blood cell
galactose-1-phosphate uridyltransferase activity. The later,
though more labour intensive, has the advantage of being able to
distinguish variants with residual activity. Both assays are
erythrocyte based and invalidated by recent blood transfusions,
though quantitative assays of both parents can be informative in
these circumstances as they can determine potential carrier
status.
Differential diagnosis
(1) Galactosaemia e There are few causes of galactosaemia
outside Leleoir pathway defects, though any significant liver
dysfunction has the potential to decrease galactose handling;
an example of this is an infant with extrahepatic portosys-
temic shunting found to be galactosaemia post feeds.
(2) Liver dysfunction e The differential diagnosis for neonatal
liver dysfunction is far wider, ranging from infections to
structural abnormalities e.g. biliary atresia, to inborn error of
� 2010 Elsevier Ltd. All rights reserved.
The routine biochemical investigations for suspected neonates with severe hepatic dysfunction
Sample Specific test Rational/finding
Urine Reducing substances Refection of tubulopathy seen in some metabolic conditions
Protein/creatinine ratio Raised with tubulopathy seen concurrently
Urine amino acids Generalized aminoaciduria in renal dysfunction especially galactosaemia
and Tyrosinaemia
Urine organic acids To insure no succinylacetone (Tyrosinaemia type 1) and organic acidemias
Stool Check pigmentation If reduced discuss with hepatology team re biliary atresia
Routine blood FBC Can show signs of haemolytic anaemia
UþEs LFTs, including GGT and clotting Reflecting of degree of liver dysfunction
Blood gas/calculate anion gap Potential acidosis reflecting renal bicarbonate loss Increase anion gap
indicative of accumulating cations e.g. organic acidaemia
UrineþBlood culture/CRP/Viral serology To look for infection To rule out Hep AeC, CMV, EBV and Parvovirus
Lactate Indication of the a disorder of the respiratory chain (NB also raised
in severe liver dysfunction)
Ferritin/LDH To insure no Haemochromatosis
Cortisol(fasting) Assessment of adrenal function
CK Potentially raised in a fatty acid oxidation disorders
Ammonia To rule out urea cycle defect
Specialized blood Acylcarnitine profile To rule out FA oxidation disorder OA
Plasma AA Raised phenylalanine, tyrosine and methionine expected
Transferrin isoelectrofocusing Indicative of CDG if positive
Chitotriosidase To look for NiemannePick C
Alpha 1-antitrypsin
Radiology Abdominal ultrasound post fast Liver, Spleen size/Hepatic vessel size/direction of flow. Bilary system
Table 1
SYMPOSIUM: INBORN ERRORS OF METABOLISM
metabolism (IEM). Thus any child with acute liver
dysfunction in the neonatal period should be thoroughly
investigated both biochemically and radiologically. Of the
IEMs, urea cycle, fatty acid oxidation disorders and organic
acidemias can present with impairment in liver function.
However the inborn error that most closely mirrors gal-
actosaemia’s presentation is tyrosinaemia type 1 which also
presents in the neonatal period with acute liver and renal
tubular dysfunction. The investigations listed above while
not an exhaustive list are designed to exclude most of the
more common causes (see Table 1).
Management
The initial management of classical galactosaemia is systemic
support for the acute toxicity and the withdrawal of exogenous
galactose. Withdrawal should be instituted immediately if
Specific investigations for Galactosaemia
Tests Sample
Screening tests Urine dipstick Urine
Galactose-1-P Blood lithium heparin (
Confirmatory tests Gal-1-Put Blood lithium heparin (
DNA Blood (EDTA 2 ml)
Table 2
PAEDIATRICS AND CHILD HEALTH 21:2 67
Galactosaemia is considered with suitable milk formulations
being either soya based preparations, or in patients with a degree
of acute hepatic dysfunction and possibly limited absorption,
Pregestimil (which still contains traces of galactose). The support
of severe liver dysfunction includes the administration of vitamin
K, antacids, the maintenance of at least 6 mg/kg/min of glucose
(often requiring high concentration dextrose, as fluid restriction
is normally recommended).
Chronic manifestations of galactosaemia
Despite early dietary intervention Glactosaemic patients may still
develop a number of long-term complications:
Neurology/motor development
Neurological manifestations linked with galactosaemia include,
diffuse cerebral oedema and pseudotumour cereberi. This is
Rational
Reducing substances positive after a lactose
containing feed galactose
minimum 1 ml) Raised in Leloir pathway defects
minimum 1 ml) To look for GALT activity NB pre transfusion
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
thought to be secondary to the osmotic action of increasing
amount of intracerebral galacticol and has only been noted in
neonates.
Some galactosaemic patients may develop a progressive
extrapyramidal disorder, which tends to manifest as tremor and
ataxia, though infantile onset of choreiform movements is also
known. The cause is unknown but functional scanning with PET
scans has shown both a decrease in activity in the cerebellum
and an increase in activity in the basal ganglia; the latter being is
also observed in Parkinsonian patients.
Significant involvement of the cerebral white matter has also
been noted, with widespread decreases in metabolism across
most of the cerebral cortex. This mirrors what has been seen on
both autopsies and neuroimaging of GALT patients. Indeed up to
1/3 of patients show some signs of cerebral atrophy on MRI
scanning, with a corresponding amount having abnormal EEGs.
However the day-to-day correlation of these changes with the
overall clinical outcome is still unclear and the precise under-
lying pathological mechanisms which result in these white
matter changes are still unknown.
Neuropsychological/language
The structural and functional changes of the cerebral white matter
underlie the verbal dyspraxia and intellectual impairment which
has been witnessed in many galactoseamic patients. Overall the
mean IQ of patientswith classical galactosaemia has typically been
found to be in the range of 70e90 though normal intelligence
has been noted. There is no evidence from the longitudinal studies
published that there is any decline in IQ with age though this
conflicts with large cross sectional studies from the early 1990s.
There appears to be a generalized impairment in both
performance related IQ and verbal IQ. One area that long been
Follow up recommendations for classical Galactosaemia patie
Recommendation
Biochemical control Gal-1-P to be kept below 150 mmol/l red cells,
50 mg/ml packed cells,
5 mg/100 ml,
0.5 mmol/g haemoglobin
Bone Calcium & bone profile. 25 OH Vitamin D levels sh
between 70e120 nmol/L
DEXA scanning 2 yearly during adolescence
Endocrinology (1) FSH/LH/oestradiol
(2) Referral to a paediatric endocrinologist by the
10 years
Gal-1-put Regular assessment of development and cognitiv
function are indicated using standardized testsd
example, Griffiths scales, Bailey scales, British ab
scales. In particular, assessment should be direc
towards early detection of speech impairment
Ophthalmology Slit lamp examination for cataract
Table 3
PAEDIATRICS AND CHILD HEALTH 21:2 68
recognized to cause particular problems for galactosaemics is
language with 56% of patients having language difficulties with
problems in articulation being particularly common i.e. verbal
dyspraxia. This appears to be related to, but is not only the result,
of the lower cognition found in patients. The overall impact of
speech therapy on outcome in galactosaemic patients is still to be
determined.
Endocrine/fertility: impairment in ovarian function was initially
noted by Kaufman et al in 1979, with over 80% of female patients
being observed to have hypergonadotorphic hypogonadism with
increased FSH levels, often from an early age. This presents
with pubertal delay or with primary or secondary amenorrhoea,
with subsequent progression to premature ovarian failure. The
proposed mechanisms for the ovarian failure include, the direct
effect of galactose and its metabolites leading to early oocyte
toxicity effects or effects secondary to hypoglycosylation of FSH,
resulting in an aberrant isoform, which is unable to induce cyclic
AMP activation. Recent work highlighting a reduction in anti-
mullerian hormone from early in life, coupled with normal
bioactivity of FSH from Galactosaemics would suggest that the
reduction in ovarian function, is through primary toxicity (at least
partially in utero), rather than due to secondary insensitivity. The
risk of premature ovarian failure does not seem to be reduced by
good dietary control, also suggesting early gonadal toxicity Some
Galactosaemia women can spontaneously become pregnant
however, with 55 reported cases in the medical literature.
There has been no convincing evidence of male gonadal
impairment and normal testosterone levels have been seen in
a number of studies.
Apart from the rise in FSH, relatively low levels of IGFBP-3
and IGF-1 have also been shown in patients of both sexes, there
nts
Frequency of review
<1 year, every 3 months
1e14 years, every 6 months
> 14 years, annually
ould be If less than <50 nmol/l then give high dose 3000e6000
u/day for 3 months then put on 400e1000 u/day ongoing
maintenance
age of
At 6 months and then at 10 years and 12 years
e
for
ility
ted
Regular local follow up with child developmental centre
review
Assessment should be made at the time of diagnosis,
then yearly until the age of 3. It should be then be
reviewed if concerns with compliance
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
has however been no incidence of defects in the thyroid function,
cortisol or prolactin profiles of 37 patients on a lactose free diet.
Bone metabolism/growth
The work of Panis et al has shown a predisposition of gal-
actosaemic patients towards generalized osteopenia in treated
children. This was despite normal levels of all trace elements,
calcium, 1,25-dihydroxy-vitamin D and PTH in 40 patients
studied. Lower IGF-1, a stimulator of osteoblast division and
matrix production, and decreased levels of carboxylated osteo-
calcin was found. Subsequently supplementation with a combi-
nation of vitamin K and vitamin D3 showed significant increases
in prepubertal Bone mineral content on Dexa scanning, leading
to their proposal of regular 2-yearly assessment with Dexa
scanning and supplementation if required. It is to be remembered
however that pubertal delay & ovarian failure will also contribute
to reduced bone mineral acquisition.
Growth in galactosaemics has been controversial with
prenatal growth/birth weight, found to be reduced or normal.
Panis et al found decreased height velocity in female patients,
with the mean corrected height when compared to mid-parental
target height Z-score was less than the target height in most
patients. The low IGF-1 and IGFBP-3 levels found were thought
to be significant, without any apparent nutritional deficiencies
being apparent in these patients. However as in the Waggoner
review, there is often apparent physiological delay with eventual
normal achievement in height. Careful monitoring of growth and
pubertal development is recommended.
Eyes/cataracts
The overall frequency of cataracts was reported initially at about
30%. Nearly half of the cataracts in this study were described as
“mild”, “transient” or “neonatal” and tended to resolve with
dietary treatment; though one neonatal onset cataract did require
surgery. However more recent reviews indicate that the rate of
cataracts is lower (14%) and none had a significant impact on
vision. There have been no recorded cases of development of
cataracts in patients who are compliant with diet.
Treatment
Long-term management is dietary, with the current recommen-
dations being to avoid lactose containing foods with no restric-
tions beyond this. The rational being that although fruit,
vegetables and offal are known to contain small amounts of
lactose, the concentration is minimal, <30 mg/day in a typical
unrestricted diet to 54 mg/day in a fruit enriched diet, when
compared to the endogenous production of galactose which has
been calculated at >1000 mg/day in a typical adult. There are
reported cases of adults homozygous for the Q188R mutation
who had discontinued their diet in early childhood without
apparent ill effects. Generally however the current recommen-
dations are to continue the use of galactose restricted diet life-
long. Those patients on this diet should insure an adequate
calcium intake.
Follow up
Ideally follow up should be based on the shared care model
between a specialized regional centre and the local paediatric
teams. The Current UK recommendations (Walter JH et al 1999
PAEDIATRICS AND CHILD HEALTH 21:2 69
see Further reading) for monitoring are listed below are listed in
the table above (Table 3).
Prevention
Unlike much of Europe and most of the United States there is no
newborn screening program for galactosaemia in the UK. The
rational behind this is that potentially clinical symptoms start
prior to when screening is performed which is usually on days
5e7, the relative infrequency of the disease and the current lack
of demonstrable impact on long-term outcome in early screened
population. Against this only 79% present by 2 months, the
diagnosis can still be missed in the presence of typical signs and
dietary treatment is started sooner where screening is performed.
While the early commencement of dietary treatment is yet to
convincingly be shown to impact on neurological outcome, this
must be balanced with the greater need of intensive care and
longer inpatient medical care, as well as the impact on the family
of having a sick infant, when with screening this is often
preventable. A
FURTHER READING
Bandyopadhyay S, Chakrabarti J, Banerjee S, et al. Prenatal exposure to
high galactose adversely affects initial gonadal pool of germ cells in
rats. Hum Reprod 2003 Feb; 18: 276e82.
Berry GT. Galactosemia and amenorrhea in the adolescent. Ann N Y Acad
Sci 2008; 1135: 112e7.
Bosch AM. Classic galactosemia: dietary dilemmas. J Inherit Metab Dis;
2010;. doi:10.1007/s10545-010-9157-8.
Bosch AM. Classical galactosaemia revisited. J Inherit Metab Dis 2006; 29:
516e25.
Bosch M, Bakker HD, Van Gennip AH, van Kempen JV, Wanders RJ,
Wijburg FA. A clinical features of galactokinase deficiency: a review of
the literature. J Inherit Metab Dis 2002; 25: 629e34.
Chhay JS, Vargas CA, McCorvie TJ, Fridovich-Keil Jl, Timson DJ. Analysis of
UDP-galactose 40-epimerase mutations associated with the interme-
diate form of type III galactosaemia. J Inherit Metab Dis 2008; 31:
108e16.
Honeyman MM, Green A, Holton JB, Leonard JV. Galactosaemia: results of
the British Paediatric Surveillance Unit study. 1988e90 Archives of
Disease in Childhood 1993; 69: 339e41.
Holton JB, Walter JH, Tyfield LA. Galactosemia. In: Scriver CR, Beaudet AL,
Sly WS, Valle D, eds. The metabolic and molecular bases of inherited
disease. 8th Edn. New York: McGraw-Hill, 2001: 1553e88.
Kaufman FR, McBride-Chang C, Manis FR, Wolff JA, Nelson MD. Cognitive
functioning, neurologic status and brain imaging in classical galacto-
semia. Eur J Pediatr 1995; 154: S2e5.
Lai K, Tang M, Yin X, Wierenga K, Elsas L. ARHI: a new target of
galactose toxicity in classic galactosemia. Biosci Hypotheses 2008;
1: 263e71.
Lia K, Elsa LJ, Wierenga KJ. Galactose toxicity in animals. Life 2009; 61:
1063e74.
Menezo YJ, Lescaille M, Nicollet B, Servy EJ. Pregnancy and delivery after
stimulation with rFSH of a galatosemia patient suffering hyper-
gonadotropic hypogonadism: case report. J Assist Reprod Genet 2004;
21: 89e90.
Panis B, Gerver WJ, Rubio-Gozalbo ME. Growth in treated classical
galactosemia patients. Eur J Pediatr 2007 May; 166: 443e6.
� 2010 Elsevier Ltd. All rights reserved.
Practice points
C Any neonate or infant with either progressive or severe liver
dysfunction should be considered to be galactosaemic and
started on either a soya based formulation or progestamil
until the results of the initial investigations are available.
C Initial investigation for Galactosaemia should include both
gal-1-P and GAL1PUT (taken prior to any blood transfusions).
C The current recommended treatment is a lifelong minimal
galactose diet, which is insured by having a lactose free diet.
C There are a number of increasingly well defined long-terms
problems, that affect SOME galactosaemic children, thus
children should continued to have regular reviews to identify
potential problems early and institute supportative measures.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Panis B, van Kroonenburgh MJ, Rubio-Gozalbo ME. Proposal for the
prevention of osteoporosis in paediatric patients with classical
galactosaemia. J Inherit Metab Dis 2007; 30: 982.
Potter NL, Lazarus JA, Johnson JM, Steiner RD, Shriberg LD. Correlates of
language impairment in children with galactosaemia. J Inherit Metab Dis
2008; 31: 524e32.
Prestoz LL, Couto AS, Shin YS, Petry KG. Altered follicle stimulating
hormone isoforms in female galactosaemia patients. Eur J Pediatr
1997; 156: 116e20.
Ridel KR, Leslie ND, Gilbert DL. An updated review of the long-term
neurological effects of galactosemia. Pediatr Neurol 2005; 33: 153e61.
Sanders RD, Spencer JB, Epstein MP, et al. Biomarkers of ovarian function
in girls and women with classic galactosemia. Fertil Steril 2009; 92:
344e51.
Schadewaldt P, Hoffmann B, Hammen HW, Kamp G, Schweitzer-Krantz S,
Wendel U. Longitudinal assessment of intellectual achievement in
patients with classical galactosemia. Pediatrics 2010; 125: 374e81.
Schweitzer-Krantz S. Early diagnosis of inherited metabolic disorders
towards improving outcome: the controversial issue of galactosaemia.
Eur J Pediatr 2003; 162: S50e3.
Tyfield L, Reichardt J, Fridovich-Keil J, et al. Classical galactosemia and
mutations at the galactose-1-phosphate uridyltransferase (GALT)
gene. Hum Mutat 1999; 13: 417e30.
Waggoner DD, Buist NRM, Donnell GN. Long-term prognosis in gal-
actosaemia: results of a survey of 350 cases. J Inher Metab Dis 1990;
13: 802e18.
PAEDIATRICS AND CHILD HEALTH 21:2 70
Walter JH, Collins JE, Leonard JV. Recommendations for the management
of galactosaemia. Arch Dis Child 1999; 80: 93e6.
Webb AL, Singh RH, Kennedy MJ, Elsas LJ. Verbal dyspraxia and galac-
tosemia. Pediatr Res 2003; 53: 396e402.
Widger J, O’Toole J, Geoghegan O, O’Kefffe M, Manning R. Diet and
visually significant cataracts in galactosaemia: is regular follow up
necessary? J Inherit Metab Dis 2010; 33: 129e32.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Peroxisomal disordersCamilla Scott
Simon Olpin
AbstractPeroxisomes are complex single-membrane cell organelles found in all
cell types except erythrocytes. Peroxisomes have both catabolic and
anabolic functions & these functions include the synthesis of plasmalo-
gens, the formation of bile acids, polyunsaturated fatty acids, cholesterol
& isoprenoids, & the degradation of very long-chain fatty acids (VLCFA’s).
Peroxisomes multiply by division of existing peroxisomes & this complex
process is regulated by both PEX & non-PEX genes. Peroxisomal disor-
ders are broadly categorized into defects of peroxisomal biogenesis
with deficiencies of multiple pathways e.g. Zellweger spectrum or defects
affecting single enzymes such as D-bifunctional protein deficiency.
Peroxisomal disorders present with a wide spectrum of clinical
disease ranging from the severe neonatal Zellweger syndrome with dys-
morphic features, neurological abnormalities, hepatorenal and gastroin-
testinal dysfunction with death typically occurring within the first 6
months of life to adult onset X-linked adrenoleukodystrophy which can
be confined only to adrenal insufficiency.
Keywords bile acids; peroxisomes; PEX genes; plasmalogens; VLCFA;
X-linked ALD; Zellweger
Introduction
Peroxisomes are complex single-membrane cell organelles found
in all cell types except erythrocytes. Peroxisomes have both
catabolic and anabolic functions & these functions predomi-
nantly involve lipid metabolism. Peroxisomal functions include
the synthesis of plasmalogens which are important constituents
of cell membranes & myelin. They are also involved in the
formation of bile acids, polyunsaturated fatty acids, cholesterol &
isoprenoids. Peroxisomes b-oxidise very long-chain fatty acids
(VLCFA’s), a-oxidise phytanic acid and catabolize lysine via
pipecolic acid and glyoxylate to glycine. Importantly they also
contain catalase which converts highly reactive hydrogen
peroxide into oxygen & water.
Peroxisomes multiply by division of existing peroxisomes.
Peroxisomal membranes are assembled & peroxisomal matrix
proteins are targeted from the cytosol & then imported into the
organelle by a highly complex process dependent on specialized
Camilla Scott MSc FRCPath is a Principal Clinical Scientist in the
Department of Clinical Chemistry at Sheffield Children’s Hospital,
Western Bank, Sheffield S10 2TH, UK. Conflict of interest: none.
Simon Olpin MSc PhD FRCPath is a Consultant Clinical Biochemist in
Inherited Metabolic Disease in the Department of Clinical Chemistry at
Sheffield Children’s Hospital, Western Bank, Sheffield S10 2TH, UK.
Conflict of interest: none.
PAEDIATRICS AND CHILD HEALTH 21:2 71
proteins termed peroxins which are encoded by PEX genes. As
a consequence peroxisomal biogenesis involves the correct
expression of multiple PEX genes of which 16 have been identi-
fied in humans. There are also a large number of single enzyme
functions within the peroxisome encoded by non-PEX genes &
defects in these results in a range of disorders with single enzyme
deficiency.
Peroxisomal disorders are broadly categorized into defects of
peroxisomal biogenesis with deficiencies of multiple pathways
e.g. Zellweger spectrum or defects affecting single enzymes such
as D-bifunctional protein deficiency. Most disorders are auto-
somal recessive, however the commonest peroxisomal disorder
X-linked adrenoleukodystrophy has an X-linked mode of
inheritance.
Peroxisomal disorders present with a wide spectrum of clin-
ical disease ranging from the severe neonatal Zellweger
syndrome with dysmorphic features, neurological abnormalities,
hepatorenal and gastrointestinal dysfunction with death typically
occurring within the first 6 months of life to adult onset X-linked
adrenoleukodystrophy which can be confined only to adrenal
insufficiency.
Peroxisomal assembly
Peroxisomal biogenesis is complex and peroxisomes multiply
by division of pre-existing peroxisomes. Peroxisomes do not
contain any DNA and subsequently all of the proteins required
for assembly and function are encoded by nuclear genes and
synthesized on free polyribosomes in the cytosol before post-
translational import into the peroxisome. Transportation is
highly selective and requires the presence of specific import
sequences known as peroxisomal targeting sequences (PTSs).
PTS1 is the C-terminal peroxisome targeting sequence and
PTS2 is the N-terminal peroxisomal targeting sequence. PTSs
are recognized by receptors (PTS1 receptor and PTS2 receptor)
which direct the peroxisomal proteins to the peroxisomal
membrane. The target protein then enters the peroxisome by
a sequential multi-step process involving recognition, dock-
ing, translocation across the peroxisomal membrane and
recycling.
All proteins (peroxins) involved in peroxisomal biogenesis
are encoded by PEX genes. To date 16 PEX genes have been
identified as essential for human peroxisomal formation. PEX5
encodes for the PTS1 receptor and PEX7 encodes for the PTS2
receptor. PEX1, PEX6 and PEX26 are required for matrix protein
import and encode proteins involved in the recycling of the
PTS1 and PTS2 receptors. PEX2, PEX10 and PEX12 encode
proteins involved in matrix protein import. PEX13 encodes
a docking factor for PTS1 and is also required for matrix
protein import. PEX3, PEX16 and PEX19 encode proteins
involved in the production of peroxisomal biogenesis proteins.
In addition to the assembly proteins, the peroxisome also
contains over 50 matrix proteins and numerous membrane
proteins.
Peroxisomal disorders
Peroxisomal disorders arise from either a defect in peroxisomal
biogenesis (the peroxisomal biogenesis defects) or a defect in
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
a single peroxisomal enzyme or protein (the single enzyme
defects).
Clinical presentation
The peroxisomal biogenesis defects include the Zellweger
spectrum which accounts for approximately 80% of patients,
while rhizomelic chondrodysplasia punctata (RCDP) accounts
for the remaining patients with peroxisomal biogenesis disor-
ders. RCDP is clinically and genetically distinct from the Zell-
weger spectrum.
The clinical phenotype of Zellweger spectrum, also known
as cerebrohepatorenal syndrome, consists of three over-
lapping phenotypes. The most severe phenotype being Zell-
weger syndrome (ZS) followed by an intermediate form,
neonatal adrenoleukodystrophy (NALD), which is not to be
confused with X-linked ALD, and the mildest form infantile
Refsum disease (IRD). The overall frequency of ZS is
approximately 1:50,000. ZS classically presents with charac-
teristic craniofacial features including large anterior fonta-
nelle, full forehead, shallow orbital ridges, epicanthal folds,
high arched palate, broad nasal bridge and small nose with
anteverted nares. Ocular abnormalities such as cataracts,
glaucoma and corneal clouding are common. In addition there
is encephalopathy, seizures, severe hypotonia, hepatorenal
abnormalities including renal cysts and skeletal abnormali-
ties. Patients usually succumb to the disorder within the first
few months of life and survival is extremely rare beyond
a year. Patients with the milder forms of the Zellweger spec-
trum have similar but less severe symptoms to ZS and
survival varies from four months to several decades. For
example, virtually all IRD patients have moderate dysmorphic
features and sensorineural hearing loss with pigmentary
retinopathy. Early hypotonia and deranged liver function are
common. However most IRD patients learn to walk, although
their gait is frequently ataxic and their mental function is in
the severely retarded range as compared to profound retar-
dation in NALD and ZS.
RCDP is clinically distinct from the Zellweger spectrum and
also has severe classical presentations and milder phenotypes.
Summary of the single peroxisomal protein/enzymedefects
Defective peroxisomal function Disorder
b-Oxidation of very long-chain
fatty acids
X-linked adrenoleukodystrophy
Acyl-CoA oxidase deficiency
D-bifunctional protein deficiency
Sterol carrier protein deficiency
a-methyl-acyl-CoA-racemase
deficiency
a-Oxidation of phytanic acid Refsum disease
Hydrogen peroxide metabolism Catalase deficiency
Glyoxylate metabolism Hyperoxaluria type I
Etherphospholipid biosynthesis DHAP-AT deficiency
Alkyl-DHAP synthase deficiency
Table 1
PAEDIATRICS AND CHILD HEALTH 21:2 72
Clinically, RCDP symptoms include characteristic proximal
shortening of the limbs (rhizomelia), cataracts, facial
dysmorphism, microcephaly, small stature, and psychomotor
retardation. For all of the peroxisomal biogenesis disorders
treatment is largely symptomatic and supportive.
Single enzyme defects
The single enzyme defects result in the loss of a single protein
and subsequently the loss of a single peroxisomal function.
Although over 50 peroxisomal matrix and numerous membrane
proteins have been identified only about 10 disorders associated
with single enzyme defects have been described, indicating that
there are many more unrecognized disorders. The known single
peroxisomal enzyme/protein defects are summarized in Table 1,
the more common/frequently encountered defects are summa-
rized below.
The most common single enzyme defect is X-linked adreno-
leukodystrophy. The inheritance is X-linked with approximately
50% of female carriers eventually presenting with clinical
symptoms. The clinical phenotypes vary from the severe child-
hood cerebral presentation through to a mild adult form. There is
a form presenting solely with Addison Disease Severe childhood
disease takes the form of a progressive demyelination of the
cerebral neurones and adrenal insufficiency. This early onset
male disease usually starts between 3 and 10 years of age with
behavioural abnormalities. Initial referral is often to a psychia-
trist or psychologist. There is further progression to dementia,
speech difficulty with loss of hearing & vision and finally
relentless progression to decorticate spastic quadriparesis, with
pigmentation of the skin secondary to adrenal insufficiency. The
most effective treatment is haematopoietic stem cell trans-
plantation which is only effective if carried out in pre-symp-
tomatic or early symptomatic patients. There is also late onset
adolescent and adult cerebral forms of X-ALD which follow
a similar but delayed course. The milder adult onset X-ALD
presents with peripheral neuropathy and Addison disease
(adrenomyeloneuropathy), with or without cognitive decline,
may affect both male and female carriers. A small cohort of X-
ALD patients will present with isolated adrenal insufficiency
(Addison only X-ALD).
Refsum disease, which should not be confused with infantile
Refsum disease, is also a single enzyme defect and is due to
defective phytanoyl-CoA hydroxylase. The enzyme is required
for the a-oxidation of phytanic acid to pristanic acid. Patients
with Refusm disease accumulate large amounts of phytanic
acid in plasma and tissues. The clinical features include;
pigmentary degeneration, peripheral neuropathy and cerebella
ataxia usually presenting before the second decade of life.
However, the age of onset and clinical severity varies according
to the degree of residual enzyme activity. Effective treatment
can be achieved by strict avoidance of dietary phytanic acid
and plasmapheresis.
D-bifunctional enzyme deficiency is a single enzyme defect
due to defective bifunctional enzyme which is required for
peroxisomal b-oxidation. Bifunctional enzyme deficiency is rare
and classically presents with neonatal hypotonia, dysmorphic
features, seizures, hepatomegaly and developmental delay. The
degree of severity is however highly variable.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Diagnostic approach
As described in the clinical section, peroxisomal disorders can
be grouped into two broad subgroups; the single enzyme
defects and the peroxisomal biogenesis disorders. The initial
diagnostic approach is similar for both groups for most disor-
ders. Along with strong clinical suspicion and a panel of
metabolites in plasma and urine, a likely diagnosis can be
reached within a couple of weeks. Most specialist metabolic
laboratories investigate three or more pathways to reach
a diagnosis. The most commonly investigated pathways
include:
� b-oxidation of the very long-chain fatty acids (VLCFA’s)
� a-oxidation of phytanic acid
� biosynthesis of ether phospholipids (plasmalogens)
� bile acid synthesis.
More detailed studies involve measuring specific enzyme activi-
ties including dihydroxyacetonephosphate acyltransferase
(DHAP-AT) in blood platelets or fibroblasts and very long-chain
fatty acid oxidation and phytanic acid oxidation in cultured
fibroblasts. A suspected or likely diagnosis from clinical and
biochemical abnormalities is usually confirmed by molecular
studies wherever possible.
The most frequently investigated pathway is peroxisomal b-
oxidation of the VLCFA’s. In plasma abnormal C26:0/C22:0
ratios are seen in both the peroxisomal biogenesis disorders
and in X-ALD. These ratios are significantly raised in the
peroxisomal biogenesis disorders and are moderately raised in
males with X-ALD. In female carriers for X-ALD the ratios are
more subtly raised and it is important to be aware that
approximately 10% of female carriers will have normal plasma
VLCFA’s. In symptomatic females it may be necessary to
measure the VLCFA’s in cultured fibroblasts, although these
will still be normal in approximately 5% of patients. In this
cohort diagnosis can only be achieved by molecular studies of
the ALD gene.
Summary of biochemical investigations for peroxisomal disor
VLCFA’s
(C22:C26)
(plasma)
Phytanic acid
(plasma)
Pristanic acid
(plasma)
Zellwegers syndrome þþþ N/þ N/þNeonatal adrenoleukodystrophy þþ N/þ N/þInfantile Refsum disease þþ N/þ N/þRCDP type 1 N N/þ N/Low
X-Linked adrenoleukodystrophy þþ N N
D-bifunctional protein deficiency þþ N/þ N/þa-Methyl-acyl-CoA-racemase
deficiency
N N/þ þ
Refsum disease N þþþ Low
Hyperoxaluria type 1 N N N
Acyl-CoA oxidase deficiency þþ N N
Catalase deficiency N N N
DHAP-AT deficiency N N N
Alkyl-DHAP synthase deficiency N N N
Table 2
PAEDIATRICS AND CHILD HEALTH 21:2 73
When a peroxisomal disorder is suspected, the second
common pathway to be investigated is the a-oxidation of phy-
tanic acid. The loss of a-oxidation results in increased phytanic
acid and if this is taken in combination with increased VLCFA’s
this strongly supports a diagnosis of a peroxisomal biogenesis
disorder. Phytanic acid is raised in isolation in the single enzyme
defect Refsum disease and clinicians should go straight to
measurements of phytanic acid when suspecting Refusm disease
on clinical grounds.
Other metabolites including red blood cell plasmalogens and
urine and plasma bile acids can also be measured to complete the
investigations for a suspected peroxisomal biogenesis disorder.
Table 2 summarizes expected results and investigations in the
single enzyme defects and in the spectrum of generalized
peroxisomal disorders.
Genetic diagnosis
Peroxisomal biogenesis disorders
Genetic diagnosis for the peroxisomal biogenesis disorders is
particularly important if future prenatal diagnosis is to be
considered. However because of the number of genes involved,
a clear strategy for investigation must be employed. Rather
than systematically working through the genes, complementa-
tion studies in cultured fibroblasts can be carried out.
Complementation involves fusing cultured fibroblasts from the
patient under investigation with fibroblasts from a cell line in
which the defect is known. The formation of peroxisomes in
the fused cell lines can be assessed by immuno-staining for the
peroxisomal enzyme catalase using fluorescent labelled anti-
bodies. If the patient has a defect in the same gene as the
known cell line, peroxisomes will not be formed, and this gene
can then be sequenced. If the patient has a defect in a different
gene then peroxisomes will be formed and further comple-
mentation studies would need to be undertaken. These elegant
studies allow identification of the defective gene in a fast and
ders
Bile acids
(urine & plasma)
Plasmalogens
(red blood cell)
DHAP-AT activity
(fibroblasts
& platelets)
Catalase
expression
(fibroblasts)
þþþ Low Low Low
þþ Low Low Low
þþ Low Low Low
N Low Low N
N N N N
N/þ N N N
þþ N N N
N N N N
N N N N
N N N N
N N N Low
N Low Low N
N Low Low N
� 2010 Elsevier Ltd. All rights reserved.
PEX deficientcell line
Patientcell line
Complementation No complementation
Cell fusion and incubation with fluorescent labelledanti-catalase antibodies
Figure 1 Complementation studies. To identify which gene is defective
cells from the patient are fused with cells from a cell line where the
gene defect is known. If the patient and known cell line share the
same defective gene there will be no complementation & no formation
of peroxisomes. If complementation is achieved peroxisomes are
formed and can be visualized by incubation with anti-catalase
antibodies.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
cost effective manor. Figure 1 demonstrates the principles of
complementation.
Over 100 mutations in PEX genes have been described in the
literature and although many mutations are private a few
common mutations have been identified. Despite many muta-
tions, the majority of patients have mutations in one of only four
of the PEX genes. PEX1 mutations account for 70% of the
peroxisomal biogenesis defects, followed by 10% in PEX6 and
5% in PEX12 and PEX26.
RCDP is genetically distinct from Zellweger syndrome spec-
trum. All mutations associated with RCDP are in the PEX7 gene
which encodes the cytosolic PTS2 receptor, Pex 7.
Single enzyme defects
Of the single enzyme defects only X-ALD will be discussed in this
review. X-ALD is caused by mutations in the ABCD1 gene. This
gene encodes for the protein ALDP which is a member of the
ATP-binding cassette (ABC) transporter protein superfamily.
ALDP is located on the peroxisomal membrane and although its
function is not fully characterized it is strongly suspected that
ALDP is involved in the transport of the VLCFA’s across the
peroxisomal membrane.
The overall incidence of X-ALD is 1:17,000 including both
hemizygotes and heterozygotes. As previously mentioned,
because not all female carriers have abnormal VLCFA’s in
plasma or fibroblasts, it is recommended that women at risk of X-
linked ALD should be screened by mutation analysis of the
ABCD1 gene.
Genetic counselling is also recommended for families when
a patient is newly diagnosed with X-ALD. De-novo mutations in
the ABCD1 gene are rare and account for less than 8% of
PAEDIATRICS AND CHILD HEALTH 21:2 74
mutations described. Genetic investigations of the extended
family have the potential not only to identify hemizygote females
but also to identify neurologically asymptomatic males with the
potential for pre-symptomatic allogenic haematopoietic stem cell
transplantation. Early diagnosis can also help to avoid Addiso-
nian crises.
It is however important to note that there is no genotype/
phenotype correlation and siblings with the same mutation may
present with very different phenotypes.
Prenatal diagnosis
Prenatal diagnosis for all of the peroxisomal disorders is carried
out using chorionic villus CV samples or cultured amniotic fluid
cells.
The poor outcome and often early death seen in the perox-
isomal biogenesis disorders and in particular in Zellweger
syndrome make prenatal diagnosis a particularly important
service for families with previously affected children. Histori-
cally prenatal diagnosis has been carried out using biochemical
techniques; in the case of Zellweger syndrome this has
involved measuring the activity of DHAP-AT on either direct
CV or cultured CV cells. False negatives and positives have
been reported using this strategy and the biochemical basis for
prenatal diagnosis currently involves measuring both DHAP-AT
activity and VLCFA concentrations in cultured fibroblasts.
Although this has improved the sensitivity, there remains the
disadvantages of the length of time taken to grow the cells, the
potential for failure of cell growth altogether and the additional
risk of maternal cell overgrowth. Increasingly now the
preferred option is to identify the mutation in the index case
and carry out molecular analysis on direct CV with cultured CV
as a back up.
Conclusion
Much has been learned about peroxisomal diseases since the first
description of a patient with X-linked ALD in 1923 & ZS in 1964.
However it took some time before a fuller understanding of
peroxisomal function & biogenesis was achieved. In the last
25 years there has been considerable advancement in our
understanding of the biochemistry & more recently the genetics
of these disorders, but much has still to be learned. To date there
is no effective treatment for many of these disorders & this great
challenge lies ahead. A
FURTHER READING
Berger J, Pujol A, Aubourg P, et al. Current and future pharmacological
treatment strategies in X-linked adrenoleukodystrophy. Brain Pathol
2010 Jul; 20: 845e56.
Braverman NE, Moser AB, Steinberg SJ. Rhizomelic chondrodysplasia
punctata type 1. In: Pagon RA, Bird TC, Dolan CR, et al., eds. Gen-
eReviews [Internet]. Seattle (WA): University of Washington, Seattle,
1993e2001 Nov 16 [updated 2010 Mar 2].
Moser HW. Clinical and therapeutic aspects of adrenoleukodystrophy and
adrenomyeloneuropathy. J Neuropathol Exp Neurol 1995 Sep; 54:
740e5 [Review].
� 2010 Elsevier Ltd. All rights reserved.
Practice points
C The clinical spectrum of disease in peroxisomal disorders is
very broad ranging from fetal death to presentation in the 3rd
or 4th decade of life.
C X-linked ALD males often first present with behavioural
disturbances and loss of acquired skills. Symptomatic female
hemizygotes are often only correctly diagnosed after presen-
tation of an index male within the extended family.
C A diagnosis of X-ALD in female hemizygotes should be fully excl-
uded by a combination of fibroblast VLCFA’s & molecular analysis.
C Exclude peroxisomal disorders in all infants with hypotonia &
dysmorphia by plasma VLCFA’s, phytanate & pristanate.
C Molecular confirmation of all peroxisomal disorders should be
sought in order to offer reliable prenatal diagnosis.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Moser HW. Genotype-phenotype correlations in disorders of peroxisome
biogenesis. Mol Genet Metab 1999 Oct; 68: 316e27.
Paprocka J, Jamroz E, Adamek D, et al. Clinical and
neuropathological picture of familial encephalopathy with
bifunctional protein deficiency. Folia Neuropathol 2007; 45:
213e9.
Semmler A, Kohler W, Jung HH, et al. Therapy of X-linked adreno-
leukodystrophy. Expert Rev Neurother 2008 Sep; 8: 1367e79
[Review].
Steinberg SJ, Dodt G, Raymond GV, et al. Moser HW peroxisome
biogenesis disorders. Biochim Biophys Acta 2006 Dec; 1763:
1733e48.
Wanders RJ, Waterham HR. Peroxisomal disorders I: biochemistry and
genetics of peroxisome biogenesis disorders. Clin Genet 2005 Feb; 67:
107e33 [Review].
Weller S, Rosewich H, Gartner J. Cerebral MRI as a valuable diagnostic tool
in Zellweger spectrum patients. JIMD 2008; 31: 270e80.
PAEDIATRICS AND CHILD HEALTH 21:2 75 � 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Lysosomal disordersJ E Wraith
AbstractAs a group lysosomal storage disorders (LSDs) are more prevalent than
phenylketonuria. Most are recessively inherited and a combination of
good clinical history, thorough physical examination and the judicious use
of X-rays can provide a clue to the diagnosis which is usually confirmed
with a combination of urine and blood tests. Disorders that affect the
brain and bone remain difficult to treat but advances in enzyme replacement
therapy have improved the outlook for many affected patients. New
approaches to therapy are in development to try and impact the CNSdisease.
Prenatal diagnosis is available for all these conditions and affected families
need to be referred to genetic services for counselling.
Keywords enzyme replacement therapy; haematopoietic stem cell
therapy; hydrops foetalis; lysosome; prenatal diagnosis
Introduction
The lysosome is an intracellular organelle with an acidic interior
containing a range of hydrolytic enzymes such as glycosidases,
proteases, sulphatases, lipases and phosphatases. These hydrolases
together with a number of integral lysosomal membrane proteins,
transporters and targeting motifs are responsible for much of the
cells inherent recycling mechanism and defects in any of these
components can result in the pathological storage of partially
metabolized substrates within the cell. This, plus the pathological
cascades initiated as a result of the lysosomal dysfunction, gives rise
to a group of monogenic disorders known as lysosomal storage
disorders (LSDs). For a comprehensive review of the pathogenic
mechanisms involved in LSDs, the reader is guided to the review by
Walkley, 2009.
Genetics, prevalence and classification
Most LSDs are inherited as autosomal recessive traits. The excep-
tions are the X-linked enzyme deficiency disorders: Fabry disease
and mucopolysaccharidosis type II (Hunter syndrome) and the
X-linked disorder of lysosomal associated membrane protein 2
(LAMP 2) known as Danon disease.
Although individual disorders are considered rare there are
a large number of them (over 50) and thus the prevalence of the
J E Wraith MB ChB MRCP (UK) FRCPCH is Honorary Professor in Paediatric
Inherited Metabolic Medicine at The University of Manchester and
Manchester Academic Health Science Centre, Central Manchester
University Hospitals NHS Foundation Trust, Department of Genetic
Medicine, St Mary’s Hospital, Oxford Road, Manchester M13 9WL, UK.
Conflict of interest: Dr. Wraith has received travel grants and honoraria
from Genzyme PLC and Shire HGT, companies that manufacture and
market enzyme replacement therapy products for LSDs.
PAEDIATRICS AND CHILD HEALTH 21:2 76
group as a whole is w1:5000 (compared to the UK prevalence of
w1:12,000 for phenylketonuria).
Historically the classification of LSDs has been based on the
nature of the primary stored material and this has generally
consisted of:
� Lipid storage disorders
B Sphingolipidoses e.g. Gaucher disease
B Gangliosidoses e.g. TayeSach’s disease
B Leucodystrophies e.g. Metachromatic Leucodystrophy
� Mucopolysaccharidoses
� Glycoproteinoses
� Mucolipidoses
� Others
This classification is however misleading as in many conditions
there is more than one storage material and in other disorders e.g.
mucolipidosis, the proposed primary storage products (mucolipids)
do not actually exist. For these reasons a classification based on the
nature of the defective protein has been suggested as an alternative
and Table 1 gives an attenuated version of such a classification.
Clinical presentation
The LSDs, like many other metabolic disorders, display a markedly
varied clinical phenotype. In some patients, the presentation may
be in utero or the newborn period, whereas in others, evenwith the
same enzyme deficiency (but usually a different genetic mutation),
onset may be in late adulthood. In addition, in most disorders the
rate of disease progression can vary widely between affected indi-
viduals even in those from the same sib ship. However, for most
patients the onset of symptoms will be in childhood often following
an unremarkable period of normal progress. The first signs may be
some slowing of developmental progress in those disorders with
a central nervous system component or in others there may be
enlargement of the liver and/or spleen or a dysmorphic facial
appearance. Recognition of individual physical signs or the eluci-
dation of an evocative clinical history will often guide the clinician
to the appropriate diagnostic tests.
Although the disorders are generalized, one organ or body
system may be affected more than others. What is common is that
all of the disorders are present from conception, all are progressive,
many involve the central nervous system and finally treatment in
many cases is palliative only.
Hydrops foetalis
Hydrops foetalis (HF) is the accumulation of oedemafluid in at least
two foetal body compartments and in LSDs this usually includes
ascites and pleural effusion. In affected pregnancies the placenta
may be large and should always be sent for detailed histological
examination in cases of HF. Although there are many causes of HF,
LSDs are responsible for a significant minority of non-immune HF
cases (up to 10% in some studies) particularly in familieswhere this
is a recurrent event.
Detailed algorithms for the clinical evaluation of the foetus or
newborn with non-immune HF can be helpful (Staretz-Chacham,
2009) and the disorders that have presented in this way are
indicated in Table 2.
In affected pregnancies a sample of amniotic fluid should be
obtained for metabolite analysis (glycosaminoglycans and oligo-
saccharides) and cell culture for subsequent enzyme analysis or
� 2010 Elsevier Ltd. All rights reserved.
Classification of LSDs based on the nature of thedefective protein
1. Defects of specific lysosomal hydrolases
a. Mucopolysaccharidoses
i. Types IeIX
b. Sphingolipidoses, other lipidoses and glycogen storage
diseases
i. Fabry disease
ii. Farber disease
iii. Gaucher disease
iv. GM1 gangliosidosis
v. GM2 gangliosidosis
vi. Krabbe disease
vii. MLD
viii. NiemannePick disease types A & B
ix. NiemannePick disease type C1
x. Wolman and cholesterol ester storage disease
xi. Pompe disease (GSD II)
c. Glycoproteinoses
i. Aspartylglucosaminura
ii. Fucosidosis
iii. a and b mannosidoses
iv. Neuraminidase deficiency
v. Schindler disease
2. Defects in post-translational modification of lysosomal proteins
a. Multiple sulphatase deficiency
b. Mucolipidosis II (I cell disease)
c. Mucolipidosis III
3. Defects in activator proteins
a. GM2 gangliosidosis AB variant
b. Prosaposin deficiency
c. Saposin A deficiency
d. Saposin B deficiency
e. Saposin C deficiency
4. Defects in structural lysosomal membrane proteins, protective
proteins, transporters and trafficking
a. LAMP 2
b. LIMP 2
c. Cathepsin A deficiency
d. Mucolipidosis IV
e. Cystinosis
f. Infantile sialic acid storage disease and Salla disease
g. NiemannePick disease type C1
5. Miscellaneous
a. Cathepsin K deficiency (Pycnodysostosis)
Table 1
Disorders that have presented with hydrops foetalis
C Mucopolysaccharidosis type VII (Sly disease) e common
C Mucopolysaccharidosis type IV
C Neuraminidase deficiency (sialidosis type II)
C Galactosialidosis
C Infantile sialic acid storage disease
C Acute neuronopathic Gaucher disease (GD II)
C GM1 gangliosidosis (b-galactosidase deficiency)
C Mucolipidosis II (I cell disease)
C NiemannePick disease type A (sphingomyelinase deficiency)
C NiemannePick disease type C
C Wolman disease (acid lipase deficiency)
C Farber disease (ceramidase deficiency)
Table 2
SYMPOSIUM: INBORN ERRORS OF METABOLISM
DNA mutation studies. In infants that survive physical and
radiological examinations may provide further clues to the correct
diagnosis.
Other neonatal presentations
Dysmorphism
A number of disorders have dysmorphic features that can be
identified at or soon after birth. In fact the infant that has
PAEDIATRICS AND CHILD HEALTH 21:2 77
a “Hurler-phenotype” at birth almost certainly does not have
mucopolysaccharidosis type IH (MPS IH). Galactosialidosis, GM1
gangliosidosis and mucolipidosis II (I cell disease) are far more
likely. The characteristic facial appearance seen in MPS IH evolves
over the first year of life and it is rare to make a diagnosis on dys-
morphic grounds before the age of 9 months except in populations
where this disorder is very common such as within the Irish trav-
elling community.
Patients with acute neuronopathic Gaucher disease (GD II) can
present with severe ichthyosis (“collodian baby”), unusual facies,
arthrogryposis, enlargement of the liver and spleen and hernias.
Another dermatological clue to the presence of underlying LSD is
the abundant Mongolian blue spots seen in children with muco-
polysaccharidoses and GM1 gangliosidosis.
Cardiac disease
In infantile Pompe disease (glycogen storage disease type II, acid
maltase deficiency), cardiac failure, cardiac arrhythmia and car-
diomegaly may all be present at birth. Indeed in a number of
affected infants cardiomegaly has been demonstrated on foetal
ultrasounds performed in the last trimester of pregnancy. Affected
infants also have macroglossia with a protruding tongue and are
generally hypotonic. In addition to the cardiomyopathy demon-
strated on echocardiography (usually hypertrophic, occasionally
dilated) there is also elevation of liver enzymes and CPK on
biochemical testing and the blood film will reveal vacuolated
lymphocytes in the vast majority of affected patients.
Hepatosplenomegaly and liver disease
Hepatosplenomegaly at birth has very many different causes and
the common ones such as bacterial and viral infections or
anatomical abnormalities need to be diagnosed quickly as
specific treatment may be available. A number of LSDs can also
be present with enlargement of the liver and spleen and in
a number of affected patients ascites will also be present. Careful
clinical and radiological examinations for other abnormalities
may be helpful and in some circumstances bone marrow or liver
biopsy may suggest underlying LSD. In contrast to this non-
specific presentation some infants with NiemannePick disease
type C (NP-C) have a very evocative clinical presentation with
liver disease in the newborn period. In these affected infants
� 2010 Elsevier Ltd. All rights reserved.
Therapy
Modality Disorders treateda
Haematopoietic stem
cell therapy (includes
bone marrow
transplantation,
umbilical cord blood
transplantation and
peripheral blood stem
cell transplantation)
MPS IH (Hurler syndrome)
Alpha-mannosidosis
Presymptomatic Krabbe
disease
Juvenile MLD (other disorders
less commonly treated
but where there is good
theoretic chance of success:
Aspartylglucosaminuria,
Farber disease, Wolman disease,
NiemannePick disease type C2)
Enzyme replacement therapy
Aldurazyme� MPS I
Elaprase� MPS II
Naglazyme� MPS VI
Fabrazyme� Fabry disease
Replagal� Fabry disease
Cerezyme� Gaucher disease
Vpriv� Gaucher disease
Uplyso� Gaucher disease
Myozyme� Pompe disease
Substrate reduction therapy
Zavesca� Gaucher disease type I in
patients for whom ERT
is unsuitable
Zavesca� NiemannePick disease type C
a Manyconditionshavebeen treatedbut this table indicatesonly thosedisorders
where significant numbers of patients are routinely referred for transplanta-
tion. For a comprehensive list of conditions that have been treated see Vellodi,
2004. By far the largest group of patients have MPS IH (Hurler syndrome).
Table 3
SYMPOSIUM: INBORN ERRORS OF METABOLISM
(about a quarter of all patients with NP-C seen in our clinic)
severe liver dysfunction often associated with conjugated
hyperbilirubinaemia suggests a diagnosis of biliary atresia and
a number of NP-C infants have had surgical procedures to
exclude this diagnosis. A significant number of these patients will
go onto develop liver failure and die (about one third) whilst the
others will slowly improve over months (and even years in some
patients) and eventually make a full recovery from their liver
disease only to present with the neurological manifestations of
the disease often many years later.
Hepatosplenomegaly in older patients may be the presenting
manifestation of Gaucher disease (types I and III) and Nie-
mannePick disease. There are often haematological abnormalities
secondary to hypersplenism and bone marrow infiltration.
Respiratory infiltration is often under recognized in these patients
who on rare occasions will present with respiratory failure.
Skeletal disease (mesenchymal presentation)
The skeletal manifestations of LSDs known as dysostosis multi-
plex (DM) usually present for the first time in the second 6
months of life depending on the nature of the underlying
disorder. DM is best seen in the vertebral bodies, hips, pelvis and
PAEDIATRICS AND CHILD HEALTH 21:2 78
metacarpals and when present the radiologist will often give the
first clue to diagnosis.
In mucolipidosis II (I cell disease) severe bone disease can be
present from before birth with severe osteopenia and patholog-
ical fractures. This presentation is often associated with a tran-
sient hyperparathyroidism demonstrated by an increased serum
parathyroid hormone and alkaline phosphatase activity with
a normal calcium concentration.
Presentation in infancy and childhood
Neurological presentation
Unfortunately a great majority of LSDs have a significant neuro-
logical component. In many disorders it is by far the dominating
clinical effect of the disease (e.g. most sphingolipidoses) whereas
in others it is merely one element of a more generalized disorder
(e.g. mucopolysaccharidosis type I).
In infantile TayeSach’s disease the onset of the neurological
disorder can seem very acute, with an explosive onset of seizures
starting towards the end of the first year of life in a patient initially
thought to be following a normal pattern of development. Rapid
neurodegeneration follows with visual loss, spasticity and even-
tually loss of all skills culminating in death before the age of 5
years in most affected infants. In these patients clinical examina-
tion reveals the classical macular “cherry red spot” secondary to
storage within the retinal cells.
The typical developmental pattern seen in LSDs is one of
regression. After a period of apparently uneventful progress,
development slows and peers start to acquire skills at an increas-
ingly faster rate. Eventually development plateaus and then
acquired skills are lost in a pattern. The most recently acquired
skills are lost first and eventually the child becomes dependent on
its carers for all needs.
For some disorders characteristic patterns can be seen. In
mucopolysaccharidosis type III (Sanfilippo syndrome) most of the
affected children are normaluntil the age of 12e18months and then
fail to develop normal speech. Initially this is usually ascribed to
associated middle ear disease and deafness. However, when this is
corrected speech fails to improve and developmental progress is
further impaired. Children with this disorder have only mild
somatic abnormalities and the facial features of anMPS disorder are
often not appreciated in this group. Diagnosis is usually established
when the patients develop the characteristic challenging behaviour
seen in MPS III. This is characterized by severe insomnia and often
extreme hyperactivity making management extremely difficult. As
the disease progresses skills are lost and the children become
unsteady and fall and also develop neurological dysphagia. Bymid-
teenage years most affected patients are dependent on their carers
for all needs before death occurs towards the end of the second or
early in the third decade of life.
Neuronal ceroid lipofuscinoses (NCL) is a group of disorders
said to be the commonest neurodegenerative disorder of child-
hood. The neurodegeneration occurs at a differing age of onset and
speed of progression depending on the type of NCL present. The
group as a whole is characterized by difficult to control seizures
and progressive visual loss. Enzyme assay and DNA mutation
analysis have made diagnosis of NCL more readily available.
NiemannePick disease type C (NP-C) can present with two
unusual but specific neurological abnormalities. The first involves
� 2010 Elsevier Ltd. All rights reserved.
Learning points
C as a group more prevalent than PKU (1:5000)
C commonest cause of non-immune hydrops foetalis
C bone and brain are commonly affected and are resistant to
treatment
C there have been important advances in enzyme replacement
therapy
C refer all families for genetic counselling as prenatal diagnosis
is possible for all of these disorders
SYMPOSIUM: INBORN ERRORS OF METABOLISM
an abnormality of voluntary eye movement due to a failure to
initiate ordinary saccades. This supra-nuclear gaze palsy initially
affects vertical movements and affected patients often blink
excessively in an attempt to initiate eye movement. This is often
the first neurological abnormality detected in affected patients.
Over time the horizontal movements are also affected and the eyes
become virtually immobile. (In Gaucher disease type III horizontal
gaze palsy develops and in these patients rapid head movements
(head thrusting) are used to stimulate eye movement.)
The second neurological abnormality seen commonly in NP-C is
cataplexy, a sudden transient loss of muscular tone precipitated by
emotion, usually humour. Patients have bouts of laughter culmi-
nating in sudden hypotonia and will fall to the ground if not sup-
ported. The attacks last seconds but can recur in bouts and can be
very disabling. Cataplexy is closely related to narcolepsy another
neurological complication seen in NP-C patients. It is important to
recognize cataplexy for what it is and not diagnose the episodes as
epilepsy as cataplexy does not usually respond to standard anti-
convulsants and ismost responsive to tricyclic antidepressants such
as imipramine.
Diagnosis
Diagnosis is based on a combination of urine analysis for char-
acteristic metabolites (mucopolysaccharidoses and glycoprotei-
noses) followed by specific enzyme assay. Most laboratories do
a lysosomal enzyme screen combining a number of assays on the
same blood sample. It is important to remember that some
disorders need more specific diagnostic tests. This includes Pompe
disease where the enzyme assay is best performed on lymphocytes
in the presence of acarbose as an inhibitor of acid glucosidase
isoenzyme. NP-C has no simple diagnostic test and a histological
diagnosis (filipin staining of skin fibroblasts) plus DNA studies are
needed to confirm the diagnosis in suspected cases.
If tests come back negative but the clinician continues to have
a strong suspicion of LSD then electron microscopy of a skin
biopsy should be performed. In all LSDs characteristic lysosomal
changes will be seen and potentially guide further diagnostic tests.
Treatment
All patients can benefit from general palliative care measures
aimed at symptom control and the treatment of reversible
complications of their disease.
Advances in the specific therapy of LSDs however have been
made over the past decade. Table 3 outlines currently available
therapies and the disorders most likely to benefit from them.
Mesenchymal tissues (e.g. bone) and brain remain the most resis-
tant to therapy and as a result formost conditions therapy cannot be
regarded as curative. In most patients there is a residual disease
burden that can be severe (e.g. skeletal disease in MPS following
bone marrow transplantation).
In primary disorders of the CNS e.g. infantile TayeSach’s
disease, treatment still remains very unsatisfactory and one can
only envisage this improving with the introduction of successful
gene therapy programmes.
Other approaches to therapy are in clinical development and are
yielding promising results in some disorders. One such treatment
involves the use of small molecules as chemical “chaperones”. In
conditions where the disorder is associated with DNA mutations
PAEDIATRICS AND CHILD HEALTH 21:2 79
leading to misfolding of the lysosomal enzymes the chaperones,
which are usually enzyme inhibitors, can bind to the enzyme
inducing stability and aid transport to the lysosome where the
chaperone dissociates. As long as themutation does not involve the
active site of the enzyme a small increase in residual enzyme
activity will result. This may, in some disorders, be sufficient to
convert a serious disorder to a more attenuated form. Chaperone
therapy for Fabry disease and Pompe disease is under development
and early clinical trials have been completed in both disorders.
Conclusions
Although rare most paediatricians will encounter one or more
LSD in their career. As treatment options are increasing, at least
for some of these disorders, it is important to make a timely
diagnosis. A combination of clinical presentation, radiology and
appropriate biochemical testing will lead to a diagnosis in most
affected patients. After diagnosis patients should be referred to
metabolic centres that have expertise in the management of these
conditions so that treatment options can be explored. A
FURTHER READING
Aldenhoven M, Sakkers RJB, Boelens J, et al. Musculoskeletal manifestations
of lysosomal storage disorders. Ann Rheum Dis 2009; 68: 1659e65.
Beck M. Therapy for lysosomal storage disorders. IUBMB Life 2010; 62:
33e40.
Parenti G. Treating lysosomal storage diseases with pharmacological
chaperones: from concept to clinics. EMBO Mol Med 2009; 1: 268e79.
Prasad VK, Kurtzberg J. Transplant outcomes in mucopolysaccharidoses.
Semin Hematol 2010; 47: 59e69.
Sanderson S, Green A, Preece MA, et al. The incidence of inheritedmetabolic
disorders in the West Midlands, UK. Arch Dis Child 2006; 91: 896e9.
Staretz-Chacham O, Lang TC, LaMarca ME, et al. Lysosomal storage
disorders in the newborn. Pediatrics 2009; 123: 1191e207.
Suvarna JC, Hajela SA. Cherry red spot. JPGM 2008; 54: 54e7.
Vellodi A. Lysosomal storage disorders. Br J Haematol 2004; 128:
413e31.
Vitner EB, Platt FM, Futerman AH. Common and uncommon pathogenic
cascades in lysosomal storage diseases. J Biol Chem 2010; 285:
20423e7.
Walkley SU. Pathogenic cascades in lysosomal disease e why so
complex? J Inherit Metab Dis 2009; 32: 181e9.
Wenger DA, Coppola S, Liu S-L. Insights into the diagnosis and treatment
of lysosomal storage diseases. Arch Neurol 2003; 60: 322e8.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Mitochondrial disease ea reviewElisabeth Jameson
Andrew AM Morris
AbstractMitochondria are the source of cellular energy. Genetically they depend on
mitochondrial genes (mtDNA) as well as nuclear genes. MtDNA inheri-
tance differs from Mendalian inheritance in many respects. As mitochon-
dria are found in all cells, mitochondrial disease has an exceptionally
wide clinical spectrum. This review summarizes the features of the clas-
sical mitochondrial disorders including the classical syndromes. The
investigation and management is also discussed.
Keywords Alpers; Barth syndrome; heteroplasmy; KearnseSayre
syndrome; Leigh syndrome; MELAS; mitochondrial disease; MERRF;
NARP; Pearson syndrome; PEO
Mitochondrial review
Introduction
Mitochondrial disorders remain challenging for the clinician due
to their unique inheritance, the myriad of clinical presentations
and diagnostic challenges. This is despite the vast progress that
has been made in our understanding of mitochondrial disease,
especially in terms of its genetics.
Mitochondria are the site for many metabolic pathways,
including the breakdown of fats and carbohydrates. Energy
released by these reactions is converted into a form that the cell
can use by the ‘respiratory chain’. This review will focus on
disorders of the mitochondrial respiratory chain.
Epidemiology
It is estimated that at least 1 in 8000 people under the age of
65 years either has or is at risk of developing a mitochondrial
disorder. Mitochondrial diseases are likely to be underestimated
as a result of the multitude of phenotypes and difficulties in
diagnosis.
Pathology
Mitochondrial biochemistry: the mitochondrial respiratory
chain consists of five ‘complexes’ floating in the mitochondrial
Elisabeth Jameson MBBCh BSc MRCPCH is a ST7 in Paediatric Inherited
Disorders of Metabolism at the Biochemical Genetics Unit, Genetic
Medicine, 6th Floor, St Mary’s Hospital, Oxford Road, Manchester M13
9WL, UK. Conflict of interest: none.
Andrew AM Morris FRCPCH PhD is a Consultant in Paediatric Inherited
Disorders of Metabolism at the Biochemical Genetics Unit, Genetic
Medicine, 6th Floor, St Mary’s Hospital, Oxford Road, Manchester M13
9WL, UK. Conflict of interest: none.
PAEDIATRICS AND CHILD HEALTH 21:2 80
membrane. Each complex has multiple subunits (46 for complex
I). When fuels are burnt in the mitochondria, ‘co-factors’ are
reduced. These co-factors are re-oxidized by the respiratory
chain, which uses the energy released to synthesize ATP (aden-
osine triphosphate).
Mitochondrial genome: mitochondria are a product of two
genomes. The nuclear genome is responsible for the vast majority
of mitochondrial proteins. The mitochondrial genome (mtDNA)
consists of a small, circular, double-stranded DNA molecule. Its
genetic codediffers from that of thenucleus, so it contains genes for
ribosomal RNA and transfer RNA as well as for some subunits of
the respiratory chain. Themutation rate formtDNA ismuch higher
than that for nuclearDNA, especially for deletions. Thismeans that
some mtDNA diseases are sporadic with a low recurrence risk in
siblings (e.g. KearnseSayre syndrome). Other mtDNA defects
show matrilineal inheritance, as described below.
Heteroplasmy and homoplasmy: there can be hundreds of
copies of mtDNA in a cell, because there are many copies in each
mitochondrion and many mitochondria per cell. A mutation may
affect all (homoplasmy) or only a fraction (heteroplasmy) of
copies of the mtDNA in a cell. Clinical problems only occur when
the level of heteroplasmy exceeds a threshold, which depends on
the severity of the mutation and the susceptibility of tissues to
impaired energy metabolism. Above this threshold, the severity
of the symptoms can vary depending on the level of hetero-
plasmy. Thus, high levels of the m.3243A>G mutation cause
MELAS syndrome (Myopathy, Encephalopathy, Lactic Acidosis
and Stroke-like episodes); but patients with lower levels may
only suffer diabetes and deafness.
Mitochondrial inheritance: inheritance of nuclear gene muta-
tions obeys Mendalian principles. In contrast, mtDNA is inheri-
ted exclusively from the mother; after fertilization of an egg, the
sperm-derived mitochondria disappear in early embryogenesis. It
is also important to know that the level of heteroplasmy can vary
from mother to child.
Figure 1 shows a typical family tree for mtDNA inheritance.
Unaffected female due to low heteroplasmy
Affected female/male respectively
Unaffected female/male respectively
Figure 1 A typical family tree for mtDNA inheritance. In the scenario
shown, the initial female carries the mutation but at a low level of
‘heteroplasmy’ and thus is clinically unaffected. Her offspring then exhibit
a variety of phenotypes. There is clearly no paternal transmission.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Presentation
Mitochondrial disease can present at any age, ranging from
neonates with severe lactic acidosis to adults with oph-
thalmoplegia. The most common symptoms are neurological
symptoms such as seizures, strokes, abnormal eye movements or
developmental delay. Mitochondrial disorders are often multi-
system and these symptoms may be accompanied by diabetes,
hearing loss, cardiomyopathy, renal tubulopathy (Fanconi
syndrome) or faltering growth. Certain combinations of features
are particularly characteristic e these classic mitochondrial
syndromes are summarized in Table 1. Mitochondrial disease can
also present with isolated symptoms, e.g. neurological degenera-
tion ormyopathy,with few additional clues. A detailed history and
examination are, therefore, crucial to define the pattern of clinical
involvement and exclude alternative diagnoses.
Investigations
Once the possibility of mitochondrial disease is raised a number of
investigations are required. In patients with clinical features sugges-
tive of a classic mitochondrial syndrome it is often appropriate to
progress straight to mutation analysis. Unfortunately, many patients
do not present so clearly and additional tests are warranted. Figure 2
shows a standard investigation pathway, with the aim to define the
phenotype and to look for alternative (possibly treatable) diagnoses.
Lactate measurement: blood lactate concentrations are often
raised in mitochondrial disease and this is a valuable clue,
Classic mitochondrial syndromes
Syndrome Clinical features
Progressive external
ophthalmoplegia (PEO)
Slowly progressive loss of eye movements and
KearnseSayre Onset is before 20 years of age with PEO, pigm
retinopathy plus at least one of ataxia, heart
and CSF protein >1 g/L
Pearson Sideroblastic anaemia and exocrine pancreati
dysfunction in infancy
MELAS Mitochondrial Encephalomyopathy, Lactic Acid
and Stroke-like episodes. Other features inclu
diabetes, deafness and cardiomyopathy
MERRF Myoclonic Epilepsy and myopathy with Ragge
Fibres. Also cardiomyopathy, dementia, deafn
Typically present in adolescence
Alpers Mild developmental delay, explosive onset of
intractable seizures, regression and cerebral a
with terminal liver failure
Leigh Onset with hypotonia or developmental delay
by 2 years. Stepwise deterioration leads to d
and brainstem problems (dysphagia, ventilati
Barth X-linked cardiomyopathy, skeletal myopathy,
neutropaenia and poor growth
NARP Neurogenic muscle weakness, Ataxia and Ret
Pigmentosa
Mutations preceded with m. are located in mtDNA. Other genes, e.g. POLG1, SURF1,
Table 1
PAEDIATRICS AND CHILD HEALTH 21:2 81
though it is a non-specific marker being raised in many other
conditions, see Box 1. Artefactually raised lactate concentrations
are to be expected if blood is obtained from a struggling child!
Raised lactate concentrations in the cerebrospinal fluid are
a more sensitive and specific marker for mitochondrial disease.
Blood and CSF lactate concentrations may, however, both be
normal, particularly in adults with mitochondrial disorders.
Radiology: magnetic resonance imaging of the brain may show
abnormalities that suggest a mitochondrial disorder. These
include symmetrical lesions of the brainstem and basal ganglia in
Leigh syndrome. In MELAS syndrome, there may be one or more
areas of infarction, predominantly affecting the cerebral cortex,
with calcification of the basal ganglia.
Muscle biopsy: this is needed in most patients and is used for
three purposes:
a) Histology. This is often normal in children with mitochondrial
disorders. Occasionally, mitochondria accumulate under the
sarcolemma, giving rise to a ‘ragged red fibre’ appearance
when stained with Gomori Trichrome.
b) Biochemical assays of the respiratory chain complexes. The
activities of complexes IeIV are measured separately, usually
in homogenized muscle. Complex V assays are less satisfac-
tory and seldom undertaken. Deficiencies may be identified in
one or more complexes. Partial deficiencies are sometimes
found and these can be hard to interpret.
Underlying defect
ptosis Variable, including single or multiple mtDNA deletions or
POLG1 mutations
entary
block
A single large scale mtDNA deletion and/or duplication
c A single large scale mtDNA deletion and/or duplication
osis
de
80% m.3243A>G, 20% other mtDNA mutations
d Red
ess.
m.8344A>G
trophy
Usually POLG1 mutations
usually
ystonia
on)
Various, including deficiencies of complex IV, e.g. due to
SURF1 mutations, complex I and pyruvate dehydrogenase
Tafazzin gene mutations
initis m.8993T>G
Tafazzin are nuclear.
� 2010 Elsevier Ltd. All rights reserved.
Detailed history, family tree and clinical examination
Baseline investigations, e.g. liver function, echocardiography,
lactate Baseline imaging if indicated, e.g. MRI head
MRI: magnetic resonance imaging, MELAS: mitochondrial encephalopmyopathy,
lactic acidosis and stroke like episodes, MERRF: myoclonic epilpesy, ragged red
fibres, NARP: neurogenic weakness, ataxia, retinitis pigmentosa, LHON: Leber’s
hereditary optic neuropathy, CSF: cerebrospinal fluid
Is there a characteristic clinical syndrome,
e.g. MELAS, MERRF, NARP, LHON, Pearson, Barth, Alpers
MUSCLE BIOPSY
± skin biopsy, CSF lactate
Molecular Genetics
Histochemistry Biochemistry
Negative
No Yes
Test for common
mutations in blood
Figure 2 The investigation of suspected mitochondrial disease.S
kil
ls
Time (years)
Episode of decompression
Stepwise decline inage-appropriate skills
Normal development
Figure 3 Stepwise progression of Leigh syndrome.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
c) Histochemistry. For complexes II and IV, this can show the
activities in individual muscle fibres. Sometimes complex IV
activity is present in some muscle fibres but absent in others,
giving a patchwork appearance; this suggests that the under-
lying defect may involve mtDNA.
When arranging muscle biopsy it is worthwhile coordinating it
with simultaneous skin biopsy and cerebrospinal fluid
sampling.
Mutation analysis: some syndromes are associated with partic-
ular genetic defects, see Table 1, and it is worth looking for these in
blood before doing a muscle biopsy. In other patients, molecular
studies are determined by the muscle biopsy results. In a patient
with Leigh syndrome due to complex IV deficiency, it may be
appropriate to sequence SURF1, a nuclear gene. In other patients,
results may point to an mtDNA defect. The mitochondrial genome
Causes of raised lactate
C Artefact due to difficult venesection
C Hypoxia
C Hypotension due to sepsis
C Cardiac disease
C Organic acidaemias
C Fat oxidation defects
C Gluconeogenesis defects
C Pyruvate dehydrogenase and pyruvate carboxylase
deficiencies
C Mitochondrial disorders
Box 1
PAEDIATRICS AND CHILD HEALTH 21:2 82
is relatively small containing 16 569 base pairs. This allows
molecular studies to be performed relatively easily. Interpretation
can be difficult due to the high percentage of benign sequence
variants and the varying degrees of heteroplasmy.
Occasionally, a patient with a mitochondrial disorder may have
normal respiratory chain results inmuscle. This may be due to tissue
specificdisease, e.g.onlyaffecting liver,ora lowlevelofheteroplasmy
in the sample. Conversely, abnormal results may be due to artefact if
samples are not processed correctly or they may be secondary, e.g.
due to some drugs used for HIV (human immunodeficiency virus).
Management and prevention
It is essential to make the correct diagnoses as some of the
differential diagnoses respond well to treatment, e.g. fat oxidation
disorders, biotinidase deficiency. Unfortunately, mitochondrial
disease seldom responds to specific treatment. A small number of
patients have ubiquinone deficiency but even these patients may
show little clinical response to treatment with ubiquinone.
Consequently, for most patients management is a supportive care
package. This may involve anti-convulsants for seizure control,
ptosis surgery, gastrostomy feeding and home care packages. At
times of acute illness, bicarbonate replacement can be used to
correct metabolic acidosis secondary to raised lactate levels. The
lack of treatment contrasts with the great progress made in iden-
tifying the underlying genetic defects. This allows genetic coun-
selling and sometimes prenatal diagnosis (if mutations are found
in a nuclear gene but it is not usually possible for mtDNA defects).
Prognosis and explanation to family
Explanation and predictions regarding prognosis are difficult due
to the rarity of these diseases, multi-system involvement,
unpredictability and complicated genetics. Explanation is even
harder when there is uncertainty about the diagnosis or the
underlying genetic defect. The prognosis depends on the clinical
presentation but even within one syndrome it is unpredictable.
Patients, especially those with Leigh syndrome, tend to run
a relapsingeremitting course with periods of stability followed
by a decompensation from which there is a failure to recover to
their previous ability and thus a stepwise decline, see Figure 3.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Follow-up
Practice points
C Mitochondrial disease has a diverse spectrum
C Phenotype and genotype do not closely correlate
C Have a low threshold for considering mitochondrial disease in
a child with multi-system pathology
C Treatment is largely symptomatic
C Prognosis is difficult to predict.
Most patients profit from seeing a specialist (in inherited metabolic
disease or neurology) and a community paediatrician, who can liaise
with local services. The pattern of disease will guide the role of the
allied health professionals. Genetic counselling for the parents, unaf-
fected siblings and thewider family is also a key part ofmanagement.
Funding
None. A
FURTHER READING
McFarland R, Taylor RW, Turnbull DM. The neurology of mitochondrial
disease. Lancet Neurol 2002; 1: 343e51.
PAEDIATRICS AND CHILD HEALTH 21:2 83
Taylor RW, Turnbull DM. Mitochondrial DNA mutations in human disease.
Nat Rev Genet 2005; 6: 389e402.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Glycogen storage diseaseChristian J Hendriksz
Paul Gissen
AbstractGlycogen storage disorders are a group of inborn errors of metabolism
characterized by accumulation of glycogen in various tissues. This accumu-
lation is the histological hallmark of these disorders although the pheno-
type shows variable overlap. Hepatomegaly, hypoglycaemia, elevated
lactate and urate with or without neutrophil dysfunction are the classical
presentations for the commonest disorders namely GSD types I a, 1b
and III. Elevated creatine kinase, weakness, hypertrophic cardiomyopathy
with or without rhabdomyolysis represent the commonest muscle subtypes
with the best known ones being GSD II, III and V. Control of glucose defi-
ciency by added calories, tube feeding or modified cornstarch is frequently
the main basis of treatment. Supportive therapies are needed to establish
near normality. Potential curative therapies are enzyme replacement thera-
pies by mode of liver transplantation, bone marrow transplantation or use
of recombinant enzyme.
Keywords bone marrow transplantation; cornstarch; enzyme replace-
ment therapy; GSD or glycogen storage disease; hypertrophic cardiomy-
opathy; inborn error of glycogen metabolism; liver transplantation;
rhabdomyolysis
Introduction
Glycogen storage diseases are a group of disorders characterized as
the name states by the accumulation of Glycogen in various tissues.
Glycogen is a branched chain polymer of glucose and is one of the
dynamic sources of glucose storage in muscle and liver. This is the
natural pattern but when there is excessive storage of glycogen in
these tissues due to enzyme deficiencies it will manifest with clin-
ical symptoms and signs that is associated within these two main
storage areas. For this reason the glycogen storage disorders are
frequently divided into those affecting primarily the liver and those
affecting muscle. This division is clinically useful as long as it is
remembered that there is some overlap and some other tissues and
organs are also affected.
The disorders were numbered as they were discovered and
assumed that they would be similar in their pathology and that the
most severe variants were discovered first followed by milder
Christian J Hendriksz MBChB MSc FRCPCH is a Consultant in Paediatric
Metabolic Medicine in the department of Clinical Inherited Metabolic
Disorders at the Birmingham Children’s Hospital NHS Foundation Trust,
Steelhouse lane, Birmingham B4 6NH, UK. Conflict of interest: none.
Paul Gissen MRCPCH PhD is a Consultant in Paediatric Metabolic Medicine
in the department of Clinical Inherited Metabolic Disorders at the
Birmingham Children’s Hospital NHS Foundation Trust, Steelhouse
lane, Birmingham B4 6NH, UK. Conflict of interest: none.
PAEDIATRICS AND CHILD HEALTH 21:2 84
variants. Over time it has become clear that they don’t share the
same pathology and there are some conceptual differences and for
that reason many of these disorders were renamed on a few
occasions causing even more confusion. With this caveat in mind
it is still useful for the generalist to remember that the lower
numbered disorders do represent the more severe end of the
spectrum and generally fasting tolerance time increases as the
numbers increase. For example Glycogen storage disorder type 1 is
usually associated with severe fasting intolerance with fasting
times as short as 45 min compared to case affected by Glycogen
storage disease type IX who may have completely normal fasting
times and frequently being diagnosed by the finding of incidental
hepatomegaly.
Glycogen storage disease type I
Type I glycogen storage disease (GSD I) is the commonest most
severe childhood form and typically presents in early infancy. First
report of patients was by von Gierke in 1929, when he described
enlarged liver and kidneys containing excessive amount of
glycogen seen at autopsy. GSD I is inherited as an autosomal
recessive condition and although there are no accurate estimates
of the incidence for GSD I, for the GSDs as a group it is approxi-
mately one in 20,000 infants.
Pathophysiology
Deficiency of hepatic glucose-6-phosphatase enzyme, which
catalyses the final step of both gluconeogenesis and glycogen
breakdown operates inside the lumen of the endoplasmic retic-
ulum and must cross the endoplasmic membrane to be effective,
was found in the initial patients with GSD I (MIM232200). In
1959 a subgroup of patients without the classical glucose-6-
phosphatase defect was described and later the defect in the
transport of gucose-6-phosphate was demonstrated. Thus the
name glycogen storage disease type Ia (GSD Ia) designates
the true enzyme defect, and glycogen storage disease type Ib
(GSD Ib) designates the transport defect. GSD Ic and GSD Id
disease subtypes had also been proposed caused by an abnormal
inorganic phosphate transport, however most of the described
patients were later found to have mutations in the gene encoding
the glucose-6-phosphate translocase and therefore also belong to
the GSD Ib group (MIM232220).
In GSD I liver is unable to generate free glucose in response
to neuro-endocrine stimuli caused by hypoglycemia. The
defect results in an accumulation of glucose-6-phosphate that
enters glycolysis, which results in increased lactate
production.
Clinical and biochemical features
Childrenwith of GSD Imay be identified in the neonatal periodwith
hypoglycemia and lactic acidosis but it is more common for the
patients to first present at 3e4 months of age with hepatomegaly
and/or hypoglycaemic seizures. GSD I patients typically have doll-
like facies (due to fat deposits in the cheeks), short stature and
protuberant abdomen due to liver enlargement although final
height is frequently normal. Kidneys are also enlarged but there is
no increase in the size of other organs.
The characteristic features of GSD I are fasting lactic acidosis and
short fasting tolerance, which may be less than 2 h, however the
� 2010 Elsevier Ltd. All rights reserved.
Practice point
C When investigating children with hypoclycaemia always check
liver size, lactate, urate and look for neutropenia.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
latter improves with age. The presence of hyperuricaemia is caused
by both decreased renal clearance and increased production of
urate. Hyperlipidaemia occurs as a result of increased synthesis of
triglycerides, VLDL, and LDL and decreased peripheral lipolysis.
Patients are at an increased risk of pancreatitis due to
hypertriglyceridaemia.
Patients with GSD Ib have neutropenia and neutrophil
dysfunction leading to recurrent bacterial infections. Although
diarrhoea is frequently seen in both GSD I types, majority of GSD
Ib patients suffer from inflammatory bowel disease, similar to
Crohn’s disease. Both GSD Ia and GSD Ib patients have abnormal
platelet aggregation and have tendency for excessive bleeding.
Although patients have very significant hepatomegaly, and there
is a universal distension of hepatocytes by glycogen and fat on
histology, there is usually no marked elevation in liver
transaminases.
The long-term complications, which are observed mostly in
adult patients following poor metabolic control, include gout,
multiple liver adenomas, and a progressive renal disease.
With early diagnosis and appropriate modern clinical
management it is thought that most of the complications can
be prevented.
The diagnosis of type I glycogen storage disease can be sus-
pected on the basis of clinical presentation and abnormal lactate
and lipid values. Previously, a definitive diagnosis required
a liver biopsy to demonstrate a deficiency. Gene mutational
analysis now allows noninvasive way of diagnosing most of type
Ia and Ib patients.
Treatment and prognosis
The main stay of treatment in GSD I is maintenance of normal
blood glucose concentrations. Normoglycaemia can be achieved
using a combination of continuous nasogastric tube feeding,
uncooked cornstarch and regular oral feeds. Most of the meta-
bolic abnormalities improve with better glycaemic control.
Nasogastric tube feeds should be started at the time of diagnosis
and may consist of modified formula feeds or glucose polymer to
provide 8e10 mg/kg/min of glucose in an infant and 5e7 mg/
kg/min in an older child. Uncooked cornstarch acts as a slow-
release form of glucose and can be administered in slowly
increasing doses in infants. Dietary intake of fructose and
galactose is usually restricted because these sugars cannot be
converted to free glucose. Allopurinol is used to help reduce the
levels of uric acid. Hyperlipidaemia can be managed with lipid-
lowering drugs such as HMG-CoA reductase inhibitors and
fibrates. Microalbuminuria is an early indicator of renal
dysfunction and can be treated with low doses of angiotensin-
converting enzyme inhibitors. In type Ib glycogen storage disease
granulocyte colony-stimulating factor is used to correct the
neutropenia and neutrophil function. In the past, many young
patients with type I glycogen storage disease died, and the
prognosis was guarded for those who survived. With the
prevention of hypoglycemia, growth and metabolic parameters
improve. In patients with extremely low fasting tolerance, severe
immune compromise and compromised quality of life the option
of liver or bone marrow transplantation can be considered.
Overall much better prognosis can be given to the patients with
GSD I, although longer follow up is required to gain a more
accurate data.
PAEDIATRICS AND CHILD HEALTH 21:2 85
Glycogen storage disease type II
Glycogen storage disease II or also called Pompe or acid maltase
deficiency is deficiency of acid alpha glycosidase (MIM 232300)
and maps to chromosome 17. It was described by Pompe in 1932
and the infantile form is distinctly different from the later onset
form of the disease. The prevalence of the infantile form is
around 1/138,000 and the later onset form around 1/57,000.
Pathophysiology
In this disease there is intra lysosomal accumulation of normal
glycogen due to abnormality of the hydrolase exporting glycogen
from the lysosomes. As the lysosomes only contribute about 3%
to energy metabolism hypoglycaemia is not a feature of this
disease but it is the destruction and accumulation inside the
lysosomes causing cell injury and loss of normal function. This
primarily affects muscle metabolism and in the infantile form
cardiac muscle is involved distinguishing it from the later onset
form where cardiac muscle is unaffected.
Clinical and biochemical features
This is a classical proximal myopathy with or without cardiac
involvement with presentation from birth to late adulthood. The
great variability depends to some extend on the functional ability of
the enzyme to degrade and storage the excessive glycogen. The
infantile form present with cardiomegaly, recurrent respiratory
infections, weakness and delayed motor milestones. Incidental
finding of a large heart and elevated creatine kinase should always
prompt the clinician to look for this rare disorder. All cases of
hypertrophic cardiomyopathy in young infants and children should
be tested for Pompe diseases as early treatment is essential.
Enlarged tongue and wood grain consistency of the muscles can
alsobe found inmost cases but depends on experience as this canbe
subtle. In older children the inability to jump, climb stairs or dia-
phragmatic weakness will also present as motor delay, frequent
falls, clumsiness, waddling gait or obstructive sleep apnoea. In the
adolescents and adults primarily weakness and sleep disturbance
due to nocturnal hypercapnia will be the main symptoms and
should be distinguished from the other more common proximal
myopathies.
Onmuscle biopsy a vacuolatedmyopathy picture can be noticed
but with specific staining it becomes clear that the excessive
glycogen is intra lysosomal.
Treatment and prognosis
Early treatment with enzyme replacement therapy has the best
outcome but this is not curative. Both mortality and morbidity are
altered by early enzyme replacement therapy and improvements
in quality of life and survival has been widely reported. Enzyme
replacement therapy (alglucosidase alpha) has been available
since 2006 and is best administered in expert centres for rare
disorders. Without treatment the infantile form is associated with
� 2010 Elsevier Ltd. All rights reserved.
Practice point
C Some patients with hypoclycaemia may developed muscle
symptoms so consider these disorders.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
early death and the later onset form with significant morbidity and
mortality. Both forms are at increased risk of death during
anaesthesia and this is particularly true for the infantile form
where arrhythmias are frequently uncovered.
Supportive therapy for infections and assisted ventilation and
wheelchair use is common in older patients. Other new treatments
are in development but not commercially available at present.
Practice point
C Hypertrophic cardiomyopathy is unusual so remember to
measure creatine kinase and look for other features of
generalized muscle disorder.
Glycogen storage disease type III
GSD III is characterized by an accumulation of abnormal glycogen
with very short outer chains in patients’ liver and muscles and was
described in 1947. This condition has an autosomal recessive
inheritance (MIM232400). Most patients are deficient in
debranching-enzyme activity in both liver and muscle (GSD IIIa).
However in 15% of patients only liver is involved (GSD IIIb).
Prevalence is about 1/100,000 but much higher in North African
Jewish communities (1/5420).
Clinical and biochemical features
In infancy and childhood, GSD III may be almost identical in
characteristics to GSD I with hepatomegaly, hypoglycaemia,
hyperlipidaemia, and delayed growth. Liver transaminases are
typically raised. Splenomegaly may be present, but the kidneys are
not enlarged. Hepatomegaly and hepatic symptoms in most GSD
III patients improve with age but progressive liver cirrhosis and
failure may occur. Hepatocellular carcinoma may occur in asso-
ciation with end-stage liver cirrhosis. In patients with GSD IIIa
muscle weakness usually becomes severe after the third or fourth
decade of life. Although ventricular hypertrophy presenting as
a cardiomyopathy is a frequent finding, cardiac failure is rare.
Diagnosis can be made by demonstrating abnormal glycogen
in liver and/or muscle and a deficient debranching-enzyme
activity in skin fibroblasts or lymphocytes. Gene mutation anal-
ysis is available and specific association of some of the mutations
with GSD IIIb disease allows sub typing of patients using DNA
analysis.
Treatment and prognosis
Dietary management is much simpler than in GSD I. In patients
with hypoglycaemia frequent carbohydrate-rich meals with
cornstarch supplementation and/or nasogastric tube feeding are
effective in maintaining good glycaemic control. Patients do not
need to restrict dietary intake of fructose and galactose. A high-
protein diet may also be effective in preventing hypoglycaemia
because protein can be used as substrate for gluconeogenesis.
Liver transplantation has been performed in patients with end-
stage cirrhosis and/or carcinoma. Unfortunately, there is no
specific treatment for the progressixve myopathy and patients
may become wheelchair bound.
PAEDIATRICS AND CHILD HEALTH 21:2 86
Glycogen storage disease IV
Abnormal glycogen with fewer branch points, resulting in a struc-
ture resembling amylopectin can be found in GSD IV patients’ liver.
This autosomal recessive disorder is caused by the deficiency of
a branching-enzyme activity (MIM232500) was described in 1956.
Mutations in the same gene can cause hepatic and neuromuscular
forms of GSD IV and there is evidence for genotypeephenotype
correlation. This is very rare and no formal incidence has been
established.
Clinical and biochemical features
This disorder is clinically variable. The typical presentation is in
infancy with failure to thrive, hepatosplenomegaly, and progres-
sive liver cirrhosis leading to death in early childhood. Patients are
unlikely to have fasting hypoglycaemia, which occurs only in
presence of significant cirrhosis.
Several neuromuscular variants of GSD IV exist and are sub-
divided into perinatal, congenital, childhood and the adult forms
depending on the age at presentation and disease severity. The
diagnosis of type IV disease requires biopsy for demonstration of
abnormal glycogen and a deficiency of branching enzyme in liver,
muscle, leukocytes, erythrocytes, or fibroblasts.Mutation analysis
can be performed in the glycogen-branching-enzyme gene.
Treatment and prognosis
There is no specific treatment for GSD IV althoughmaintenance of
normoglycaemia and adequate nutrition may improve liver
function and muscle strength and improve long-term outcome for
growth in some patients. Liver transplantation is an effective
treatment for patients with progressive liver disease. The majority
of patients will die in childhood either due to liver failure or severe
cardiomyopathy and associated neurological dysfunction. There
seem to be amilder subgroupwith non progressive liver disease or
adult onset neurological disease and normal survival is expected
in this subgroup.
Glycogen storage disease type V
This was described in 1951 by McArdle and also known as myo-
phosphorylase deficiency or PYGM deficiency (MIM 232600) and
most of those affected have nearly no activity of the enzyme and
complete inability to convert glycogen to glucose inmuscle. This is
a rare autosomal recessive condition with an incidence of about
one in 100,000 and the defect is located on chromosome 11. Most
cases are diagnosed in their 20’s or 30’s although with careful
history the symptoms are present from a young age but can be very
non specific.
Clinical and biochemical features
In young children the presence of muscle aches and pains can
easily be ignored and a history of myoglobinuria is seldom
established. Parents are usually unaware of children passing dark
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
coloured urine and as it is painless it is hardly ever offered in the
list of concerning features in the clinical history. The condition is
also classically associated with second wind phenomena where
the patient would start an activity and then stop due to pain but
after a short period of rest is able to complete the activity. This is
also a progressive disorder so with increasing age the symptoms
and signs becomes more prominent starting from muscle aches
and pains to muscle cramps, myoglobinuria and then ultimately
rhabdomyolysis and renal failure during the acute episode.
Persistent weakness and increasing disability represents the full
blown picture in older patients. Some incidental findings may
also lead to diagnosis and creatine kinase levels are mildly
elevated in most cases. Electromyography may show non specific
myopathic changes or increased muscle irritability.
Diagnosis is by measuring the specific enzyme deficiency in
muscle biopsy samples or by molecular analysis. The histological
changes in muscle biopsy tissue may also point towards this
diagnosis and the presence of subsarcolemmal normal looking
glycogen in vacuoles will alert the astute histopathologist. Vacu-
olar myopathic changes are associated with many conditions and
only by specific staining techniques can the different chemicals be
distinguished.
Differential diagnosis can bewide especially in the young where
muscle aches and pain and elevated creatine kinase is associated
with muscular dystrophies, other glycogen storage disorders,
disorders of fatty acid metabolism and other rare disorders like
Danon’s disease. Weakness and disability in the older patients
share many similarities with other muscular disorders and rhab-
domyolysis is associated with certain drugs or viral infections.
Treatment and prognosis
There is no specific treatment at present and life style modifica-
tion supported by some dietary measures may be useful. Exces-
sive weight gain lowers the aerobic threshold and gentle exercise
will have beneficial effect on this as well.
This disorder has a relatively benign long-term outcome as
significant morbidity and mortality is associated with rhabdo-
myolysis and acute multi organ failure and a rare neonatal form
causing respiratory failure but both these two complications are
rarely seen. More frequently the symptoms and loss of function
over time is controlled by ability. There is increased risk with
certain anaesthetic agents and anaesthetist should be made aware
of this condition and change the drugs as needed.
Genetic counselling is possible in most cases and the condi-
tion carriers no increased risk during pregnancy.
Practice point
C When investigating fatigue always ask for history suggesting
second wing phenomena.
Glycogen storage disease VI
GSD VI also called Hers disease is due to deficiency of glycogen
phosphorylase (MIM232700) and was described in 1959. It has
an incidence of 1/60,000e85,000. GSD VI, VIII and IX are
frequently considered as a single entity.
PAEDIATRICS AND CHILD HEALTH 21:2 87
Clinical and biochemical features
This condition usually present with hepatomegaly and growth
retardation early in childhood. Ketotic hypoglycaemia and hyper-
lipidaemia are usually mild, if present. Lactic acid and uric acid are
typically normal. The heart and skeletal muscles are not involved
and the hepatomegaly improves with age and usually disappears
around puberty.
Although these patients have greatly diminished activity of
phosphorylase in the liver, the number of patients with primary
defect in phosphorylase is small whereas deficiency in phos-
phorylase kinase activity (GSD IX) is much more common.
Mutation analysis of liver phosphorylase gene is available for
the diagnosis.
Treatment and prognosis
A high-carbohydrate diet and frequent feeding are effective in
preventing hypoglycaemia, but most patients require no specific
treatment and incidental finding of asymptomatic hepatomegaly
is the commonest finding.
Glycogen storage VII
GSD VII also called Tarui’s disease caused by deficiency of
phosphofructokinase (MIM 232800) is a very rare disorder with
about 100 cases described in the literature since first reported in
1965.
Clinical and biochemical features
The clinical features are a combination of exercise induced
muscle cramps, weakness and haemolytic anaemia. It is also
associated with myoglobinuria, rhabdomyolysis and growth
delay. Cataracts, gall stones and increased uric acids have also
been described.
Treatment and prognosis
There is no specific treatment and ingestion of glucose before
exercise can sometimes exacerbate symptoms or the so called
“out of wind phenomena”. Great clinical variability exits with
severe fatal neonatal form to asymptomatic late onset variants
that may not be diagnosed.
Glycogen storage disease IX
Patients with GSD IX have a deficiency in phosphorylase b kinase,
which can be demonstrated in leukocytes and erythrocytes. These
patients were initially described as GSD IV when deficient phos-
phorylase activity was found. This condition can be inherited in an
autosomal recessiveorX-linked form(initially classifiedasGSD-VIII).
The cause of the confusing numerical classification was due in
part to a lack of understanding of the genetics of phosphorylase
activating system. Phosphorylase kinase consists of four subunits
encoded by different genes on different chromosomes and
differentially expressed in different tissues.
Clinical and biochemical features
X-linked GSD IX: X-linked liver phosphorylase kinase deficiency
occurs in approximately 75% of GSD IX (MIM306000). Besides
liver, enzyme activity also may be deficient in erythrocytes,
leukocytes, and fibroblasts. Typically patients present aged 1e5
years with protuberant abdomen due to hepatomegaly, growth
retardation, and slight delay in motor development, dyslipidaemia
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
and mild elevation of liver transaminases. These abnormalities
gradually disappear with age, and most adult patients are practi-
cally asymptomatic despite a persistent phosphorylase kinase
deficiency. Hypoglycemia is variable and usually is mild, if present.
Autosomal recessive GSD IX: autosomal phosphorylase kinase
deficiency can be present in (1) liver-specific, (2) liver and
muscle and (3) muscle-specific forms (MIM261750). As with the
X-linked form, in (1) hepatomegaly and growth retardation are
the predominant symptoms in childhood. In addition some of
these patients are hypotonic. Some cases of phosphorylase
kinase deficiency restricted to muscle have been reported and in
whom onset of symptoms was late (adolescence or adulthood),
however GSD IX patients with childhood presentation of myop-
athy have been described. Muscle-specific phosphorylase kinase
deficiency could be inherited in an X-linked or autosomal
recessive manner. Establishing the diagnosis of type IX glycogen
storage disease is challenging owing to underlying genetic
heterogeneity and variable expressivity. The deficiency of phos-
phorylase kinase is not consistently detectable by the erythrocyte
assay, and liver, muscle, or heart biopsy is necessary to confirm
some cases biochemically. The enzyme assay is also unable to
differentiate between patients with X-linked and an autosomal
recessive pattern of inheritance. Thus, in many instances,
mutation analysis is needed for further sub typing of the disease.
Treatment and prognosis
Practice pointC Remember to check urine dipsticks as a minimum in all
patients with hepatomegaly.
A high-carbohydrate diet and frequent feedings are effective in
preventing hypoglycaemia, but most patients require no specific
treatment. Prognosis is usually good; adult patients have normal
stature and minimal hepatomegaly. Out of all GSD IX patients the
autosomal recessive form typically has a more severe clinical
course with progressive liver disease.
Practice point
C Glycogen storage disorders is only one of the causes of iso-
lated asymptomatic hepatomegaly and specialist help may be
needed as some of these seemingly innocent conditions may
have significant health effects in later life.
Glycogen storage disease X
GSD X or phosphoglycerate mutase deficiency (MIM 261670) is
a rare disorder with a few isolated cases reported. It is a benign
disorder presenting with muscle cramps and weakness after stren-
uous exercise. Diagnosis is by molecular analysis of PGAM2 gene
located in chromosome 7. Patients are at risk of rhabdomyolysis but
full recovery seems to follow with appropriate treatment.
Glycogen storage disease XI
GSD XI or also called FanconieBickel Syndrome is actually
a disorder of glucose transport metabolism caused by mutations in
the gene encoding the glucose transporter 2 (GLUT2). GLUT2 is
expressed in the membranes of hepatocytes, pancreatic beta cells,
and the basolateral membranes of intestinal and renal epithelial
PAEDIATRICS AND CHILD HEALTH 21:2 88
cells where it facilitates bilateral glucose transport. FanconieBickel
disease is characterized by proximal renal tubular dysfunction,
abnormal regulation of glucose homeostasis, and accumulation of
glycogen in liver and kidneys. Patients present in the first year of life
with failure to thrive, rickets, and a protuberant abdomen due to
hepato- and renomegaly. Moon-shaped facies and fat deposition in
the shoulders and abdomen are seen and puberty is delayed.
Hypophosphataemic rickets and osteoporosis are constant features.
These patients may exhibit intestinal malabsorption and diarrheoa.
Laboratory findings include fasting ketotic hypoglycaemia,
proximal renal tubular acidosis, hypophosphataemia, increased
serum alkaline phosphatase levels, and radiologic findings of
rickets. Liver transaminases, plasma lactate, and uric acid are
usually normal. Fasting hypoglycaemia and hepatomegalymay be
explained by an altered glucose transport out of the liver, resulting
in an increased intracellular glucose level that inhibits glycogen
degradation, leading to the glycogen storage. Hypoglycaemia is
exacerbated by renal loss of sugars across the basolateral
membranes in the proximal tubular cells.
Treatment is symptomatic paying attention to replacement of
water, electrolytes, and vitamin D, restriction of galactose intake.
Patients are managed with frequent small meals with cornstarch
supplementation and an adequate caloric intake, however,
growth retardation persists despite interventions.
Glycogen storage disease XII
GSD XII is a disorder of red blood cell aldolase A deficiency
(MIM 611881). Presenting features are haemolytic anaemia,
developmental delay and hepatomegaly due to glycogen accu-
mulation. Muscle weakness and rhabdomyolysis have also been
described and this seems to be a variable condition with unpre-
dictable prognosis.
Glycogen storage disease XIII
This very rare disorder has been described in a single case and is
due to deficiency of enolase Beta (MIM 612932). In this case
elevated creatine kinase, myalgia and exercise intolerance were
described.
Glycogen storage disease 0
Patients with GSD0 have a deficiency of liver glycogen synthase
with autosomal recessive inheritance (MIM240600). Glycogen
synthase catalyses the elongation of chains of glucose molecules
to form glycogen and is not involved in glycogen breakdown.
The patients usually present in early infancy with early-
morning drowsiness and fatigue and sometimes with convulsions
associated with ketotic hypoglycaemia. There is no hepatomegaly
or hyperlipidaemia. Postprandial hyperglycemia and a rise in
blood lactate concentration are typically seen. Occasional muscle
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
cramping has also been reported suggesting hepatic and muscle
variants.
Treatment is symptomatic and involves frequent high-protein
feeds and nighttime supplementation with uncooked cornstarch.
Most children do not suffer neurocognitive damage. Short stature
may occur, but no other long-term complications seen in GSDs
have been described.
Muscle glycogen synthase deficiency was reported recently in
patients with muscle glycogen synthase gene mutations
(MIM611556). Clinical features included hypertrophic cardio-
myopathy and sudden cardiac arrest at the age of 10, and skeletal
muscle fatigability.
Practice point
C Postprandial hyperglycaemia is frequently missed and can
point towards one of these disorders.
Conclusion
Although the accumulation of glycogen forms the basis of most
these disorders for the clinician there are only a few important
messages to take away. The combination of both muscular and
hepatic symptoms should make the clinicians suspect these disor-
ders. Other classical features are hypoglycaemia, increased serum
lactate and urate. Elevated creatine kinase and muscular weakness
with associated rhabdomyolysis are also important triggers.
Hypertrophic cardiomyopathy is a frequent association and post-
prandial hyperglycaemia is found in both GSCD 0 and GSD XI.
Attenuated formsmay present with asymptomatic hepatomegaly or
being diagnosed incidentally from either liver or muscle biopsy
specimens.
The main stay of treatment is control of hypoglycaemia and
other associated features. Supportive treatment is important and
PAEDIATRICS AND CHILD HEALTH 21:2 89
enzyme replacement therapy in the form of liver transplantation,
bone marrow transplantation or recombinant enzyme gives the
greatest hope for those affected by severe phenotypes. A
FURTHER READINGELECTRONIC RESOURCES
http://emedicine.medscape.com/pediatrics_genetics#metabolic.
http://www.agsd.org.uk/.
http://www.patient.co.uk/doctor/Glycogen-Storage-Disorders.htm.
TEXTBOOKS
Chen YT. Glycogen storage diseases. In: Scriver CR, Beaudet AL, Sly WS,
eds. The metabolic and molecular bases of inherited disease. 8th Edn.
New York, NY: McGraw-Hill, 2001: 1521e51.
Smit GPA, Rake JP, Akman HO, et al. The glycogen storage diseases and
related disorders. In: Fernandes J, Saudubray JM, Berghe G, Walter JH,
eds. Inborn metabolic diseases: diagnosis and treatment. New York,
NY: Springer, 2006. Chap 6.
JOURNALS
Heller S, Worona L, Consuelo A. Nutritional therapy for glycogen storage
diseases. J Pediatr Gastroenterol Nutr 2008 Aug; 47(suppl 1): S15e21.
Ozen H. Glycogen storage diseases: new perspectives. World J Gastro-
enterol 2007 May 14; 13: 2541e53.
Rake JP, Visser G, Labrune P, et al. European Study on Glycogen Storage
Disease Type I (ESGSD I). Guidelines for management of glycogen
storage disease type I e European Study on Glycogen Storage Disease
Type I (ESGSD I). Eur J Pediatr 2002 Oct; 161(suppl 1): S112e9.
van Adel BA, Tarnopolsky MA. Metabolic myopathies: update 2009. J Clin
Neuromuscul Dis 2009 Mar; 10: 97e121.
Visser G, Rake JP, Labrune P, et al. European Study on Glycogen Storage
Disease Type I. Consensus guidelines for management of glycogen
storage disease type 1b e European Study on Glycogen Storage
Disease Type 1. Eur J Pediatr 2002 Oct; 161(suppl 1): S120e3.
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Medium-chain acyl-CoAdehydrogenase deficiency ea reviewElisabeth Jameson
John H Walter
AbstractMedium-chain acyl-CoA dehydrogenase deficiency (MCADD) is an auto-
somal recessive disorder of fatty acid oxidation with an incidence in the
UK of more than 1:10,000. The majority of patients are homozygous for
a missense mutation c.985A>G. Newborn screening for this condition
was implemented nationally in England and Northern Ireland in 2009
and is planned for Scotland in 2011. Patients with MCADD are at risk
during periods of fasting stress, particularly during intercurrent infections,
of developing an encephalopathy associated with hypoketotic hypogly-
caemia. These can be prevented by giving high calorie drinks (the emer-
gency regimen) during periods of illness but hospital admission is
required for intravenous dextrose if the emergency regimen is not toler-
ated. No specific treatment is required at other times. This review high-
lights the pathogenesis, the presentation and management of MCADD.
Keywords emergency regimen; fatty acid oxidation disorder; hypo-
glycaemia; MCADD; medium-chain acyl-CoA dehydrogenase deficiency
MCADD review
Definition
Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is
an autosomal recessive disorder of mitochondrial beta oxidation
of medium chain length fatty acids. It is caused by mutations in
the ACADM gene.
Epidemiology
The disorder is panethnic but more common in Caucasians with
an incidence of one in 6000e10,000. 60e80% of symptomatic
patients are homozygous for the c.985A>G missense mutation. A
further 15e20% are compound heterozygous for c.985A>G in
combination with another mutation. The prevalence of the
common mutation likely reflects a founder effect and is thought
to have originated in northwest Europe. The genotypes in those
detected by newborn screening are more diverse suggesting that
Elisabeth Jameson MBBCh BSc MRCPCH is an ST7 in Paediatric Inherited
Disorders of Metabolism in the Biochemical Genetics Unit, Genetic
Medicine, 6th Floor, St Mary’s Hospital, Oxford Road, Manchester, M13
9WL, UK. Conflict of interest: none.
John H Walter MD FRCPCH is a Consultant in Paediatric Inherited
Disorders of Metabolism in the Biochemical Genetics Unit, Genetic
Medicine, 6th Floor, St Mary’s Hospital, Oxford Road, Manchester, M13
9WL, UK. Conflict of interest: none.
PAEDIATRICS AND CHILD HEALTH 21:2 90
some mutations are of less clinical significance. However, at
present it is wise to assume that an individual with any mutation
associated with persistent abnormal biochemistry (see below) is
at risk from clinical illness caused by MCADD.
Pathology
In the normal post-absorptive state there is a fall in glucose
concentrationwith a parallel fall in insulin. This results in a release
of compensatory hormones and a reduction in glucose use by
muscles and peripheral tissues. Release of glucose from glycogen
(glycogenolysis) initially satisfies energy demands. However,
energy production from the oxidation of fats becomes increasingly
important both to decrease the dependency on the limited stores of
glycogen and to produce ketones that can be used as an alternative
to glucose as a fuel for the brain. This is especially important in
young children whose cerebral glucose requirements are high and
whose physiological response to periods without enteral feeds is
accelerated when compared with that in adolescents and adults.
The oxidation of fatty acids is shown in Figure 1. Fatty acids
released from triglycerides enter the mitochondria and subse-
quently undergo b-oxidation, a process bywhich the fatty acyl-CoA
molecule is sequentially shortened by two carbon units until it is
completely converted to acetyl-CoA. Electrons released from
b-oxidation enter the respiratory chain to produce ATPwhereas the
majority of the acetyl-CoA produced is converted to ketones by the
liver. Acyl-CoA dehydrogenase enzymes within this b-oxidation
cycle have activities that are chain length specific:MCAD (medium-
chain acyl-CoA dehydrogenase) hasmaximum activity for C6eC10
fatty acids. Due to a degree of overlap in chain length specificity
otherb-oxidationdehydrogenases are able tooxidisemediumchain
fatty acids and produce ketones when flux through the pathway is
low. This explains why patients with MCADD are generally able to
tolerate overnight fasting. However during periods of increased
requirements for b-oxidation there is an accumulation of medium-
chain fatty acyl-CoA derivatives and reduced acetyl-CoA and
ketone production resulting in clinical illness.
Newborn screening
Newborn screening for MCADD by tandem mass spectroscopy
underwent evaluation in England between 2004 and 2006 and
was implemented nationally in England and Northern Ireland in
2009. Screening is planned for Scotland in 2011. See ‘diagnosis’
section for further detail on newborn screening.
Clinical presentation
The classic presentation is of encephalopathy with hypoketotic
hypoglycaemia. It is important to recognize that the child may
have developed an acute encephalopathy prior to the fall in blood
glucose, which can lead to diagnostic confusion. It typically
presents between the ages of 3 and 24 months when the child
experiences their first ‘fast’ associated with an intercurrent infec-
tion (often gastroenteritis) or being placed nil by mouth prior to
a surgical procedure. The child will typically become increasingly
lethargic with nausea or vomiting which rapidly progresses to
coma. Hepatomegaly and hypotonia are often present. Tests done
at the time will show evidence of hepatocellular dysfunction,
hypoglycaemia, hypoketosis (the presence of ketones does not
exclude the diagnosis) and mild-moderate hyperammonaemia. If
the low blood sugars are not detected the child may suffer
� 2010 Published by Elsevier Ltd.
Triglyceride stores
Long chain fatty acid
Carnitine Acyl carnitine
Carnitine
Ketone bodies
Dicarboxylic acidsAcetyl-CoA
Medium chain fatty acid
-oxidation -oxidation
Cytoplasm
Mitochonrion
Mitochonrial membrane
Figure 1 Fatty acid oxidation. Triglycerides are mainly composed of long chain fatty acids which require transfer across the mitochondrial membrane as an
acylcarnitine. Medium chain fatty acids can cross the mitochondrial membrane directly. Within the mitochondrion fatty acids then undergo b-oxidation in
which the fatty acid molecule is sequentially shortened by two carbon units releasing acetyl-CoA. Certain enzymes involved in b-oxidation, including
MCAD, are chain length specific. Deficiency of this enzyme prevents the normal catabolism of both long and medium chain fatty acids and results in an
increase in medium chain acylcarnitines in blood, increased u-oxidation to form dicarboxylic acids, and a reduction in ketone body production.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
a seizure, permanent neurological damage secondary to cerebral
oedema and in the worst-case scenario death. In unscreened
populations up to 25% of patients with MCADD have died in their
first episode. Sudden unexpected death in infancy (SUDI) may be
caused by undiagnosed MCADD but it is not a cause of true
Sudden Infant Death Syndrome (SIDS); generally there is always
a preceding illness associated with poor feeding.
Diagnosis
Case example of early neonatal death resulting fromMCADD
Baby 1 was born at term following an uneventful pregnancy. He
was observed on the post-natal for 24 h in view of prolonged
rupture of membranes. He was discharged home the next day on
breast feeds. On day 2 of life he appeared pale, though was
feeding well. Later that day he became apnoeic and required
resuscitation and transfer to a paediatric intensive care unit. A CT
Newborn screening: newborn screening relies on tandem mass
spectrometry to detect raised C8 (octanoylcarnitine). C8 has been
found to be both a specific (low number of false positives) and
sensitive (low number of false negatives) marker for MCADD,
particularly if combined with measurement of the C8/C10 acyl-
carnitine ratio. In addition to raised C8 there is also an increased
urine hexanoyl glycine. Table 1 highlights the key biochemical
findings in MCADD.
In the UK the newborn screening programme specifies that
blood should be collected on filter paper between days 5e8 of life.
Biochemical findings in MCADD
Investigation Result
Blood sugar Normal or low
Urinary or plasma ketones Low or absent
Urine organic acids Raised C6eC10 dicarboxylic acids
(adipic, suberic and sebacic),
hexonylglycine, suberylglycine and
phenylpropionylglycine
Blood acylcarnitines Raised octanoylcarnitine (C8) and
decanoylcarnitine (C10)
Table 1
PAEDIATRICS AND CHILD HEALTH 21:2 91
Where MCADD screening is undertaken the large majority of
affected infants are now detected within 2 weeks of birth.
However, there are three groups of children who may still present
symptomatically and in whom the diagnosis must be considered:
1. Newborns prior to the result of the newborn screening (due
to inadequate breast-feeding or neonatal infection), see case
example below in Box 1.
head scan was consistent with hypoxic-ischaemic encephalopathy
and he remained encephalopathic. The decision to withdraw life
support was made. The cause of death was thought to be sepsis,
however the results of a blood spot acylcarnitine analysis showed
a markedly increased C8 of 10.7 mmol/l. Urine organic acids
showed heavy dicarboxylic aciduria with traces of abnormal
glycine conjugates but with no ketones. Mutation analysis went on
to confirm the baby was homozygous for the common MCADD
mutation c.985A>G.
The family’s older children will undergo mutation analysis,
even though their newborn screen was negative. Any future chil-
dren will be treated as potential MCADD sufferers until tests
results are back.
Box 1
� 2010 Published by Elsevier Ltd.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
2. Children born prior to the newborn screening program.
3. Children born in other countries where screening does not
take place.
Symptomatic: a child, who presents with a blood sugar less than
2.6mmol/l, should undergo a number of investigations at the time
of the hypoglycaemia (Table 2). However this may not always be
achieved. Characteristic abnormalities in the urine organic acids
may be transient so that samples collected when patients have
recovered from an episode may not be diagnostic. Blood octa-
noylcarnitine, however, is always increased in MCADD.
Differential diagnosis
The differential diagnosis includes those disorders that cause
encephalopathy and hypoglycaemia. Hypoketosis is associated
with other inherited disorders of fatty acid oxidation and with
hyperinsulinism. A significant ketosis is a feature of the majority
of other causes. A careful clinical history and the investigations
listed in Table 2 will usually confirm the correct diagnosis.
Management
Acute illness: it is important to emphasize that a child with
MCADD may become seriously unwell before the blood sugar
falls and it is imperative to treat early. All children with MCADD
should have an emergency regimen for use at times of illness.
The aim of the emergency regimen is to provide a source of
energy and thus prevent hypoglycaemia. The emergency regimen
consists of drinks usually of soluble glucose polymer (e.g. Max-
ijul or Polycal) though some families use alternatives in discus-
sion with a specialist dietician.
The principles of management of an unwell child with
MCADD are given below, further detail can be found on the
‘British Inherited Metabolic Disease Group’ (BIMDG) website
including emergency regimes; see http://www.bimdg.org.uk/.
Stage 1. If the child is not their usual self or may be at risk of
illness (for example post-immunization) give regular oral drinks
and reassess in 2e4 h. If the child is better when re-assessed then
they go back to their normal diet, if unwell then go to stage 2.
Stage 2. Regular drinks of the emergency regime to be given day
and night as per the child’s individual regime. This treatment
should continue until the child improves. If the child does not
improve go to stage 3.
Investigations to be taken at the time of hypoglycaemia
Blood Urine
Glucose Ketones
Acylcarnitines Organic acids
Free fatty acids and 3(OH) butyrate Reducing substances
Amino acids
Ammonia
Lactate
Growth hormone, cortisol, thyroid function,
insulin, C-peptide
Table 2
PAEDIATRICS AND CHILD HEALTH 21:2 92
Stage 3. If the child is obviously not well, not tolerating or not
taking drinks or the family areworried contact or go to the hospital.
Stage 4. If the child is not tolerating or taking the emergency
drinks then the child will need intravenous 10% dextrose/0.45%
saline. Try to re-establish normal diet within 48 h.
Intravenous fluids with 10% dextrose/0.45% saline must also
be used if the child is nil by mouth prior to a surgical procedure.
Long term management: throughout life the emphasis is to
prevent fasting.UK recommendations for themaximumage related
fasting time are given in Table 3. MCADD is not a contraindication
to breast-feeding but bottle top-ups may be needed particularly in
the first few days after birth. Formulas made with medium chain
triglycerides are contraindicated. Weaning can be commenced at
the usual time of 6 months under the guidance of a dietician. Once
toddler age is reached the child needs to have threemeals a day and
a bedtime snack. Missed meals should be replaced with a starchy
snack or sugary drink. A normal diet should be encouraged as the
child grows but with inclusion of regular starchy foods. It is
important that the child’s school is aware of his/her disorder and is
able to recognize symptoms thatmight be related toMCADD.Once
the child reaches adolescence the issue of excess alcohol should be
addressed in view of the risk of hypoglycaemia secondary to inhi-
bition of gluconeogenesis. Individuals with MCADD are at poten-
tial risk from their disorder throughout life and should remain
under review when they reach adulthood.
Siblings of MCADD patients: since MCADD is an autosomal
recessive condition, new siblings have a one in four risk of being
affected. A summary of the guidelines for their initial manage-
ment after birth, provided by BIMDG, is as follows:
� Investigations should be undertaken between 24 and 48 h of
age with blood spot acylcarnitines, urine organic acids and
DNA mutation analysis. Cord blood is not suitable because of
the risk of maternal contamination.
� A term baby should be fed every 4 h and a preterm every 3 h.
Potential problems associated with breast-fed babies are diffi-
culties in quantifying the amount of breast milk taken and the
low supply of breast milk in the first 72 h. These babies may
need formula top-ups. If there are any concerns at all the baby
should be transferred to the neonatal unit for blood sugar
monitoring with appropriate management, i.e. formula feeds
or intravenous 10%dextrose. Thesemeasures should continue
until acylcarnitine and urine organic acid results are known.
Older siblings of patients detected by newborn screening, who
were born before screening was started or born in countries
Recommended fasting times for children with MCADDwhen well
Age of child Maximum safe fasting time (h)
0e4 months 6
From 4 months 8
From 8 months 10
From 12 months onwards 12
Table 3
� 2010 Published by Elsevier Ltd.
Case example of child detected by newborn screening
Baby 2 was born at term following an uneventful pregnancy. She
was a breast-fed infant. She had standard blood spot testing
performed on day 5 of life. This revealed a raised C8 and C10. The
result was available on day 8 and immediately passed to the
metabolic service. The GP was contacted that day and asked to
visit the family to ensure the infant was well and to inform them
that an appointment had been arranged for the baby to be seen
the following day. The next day she was seen by the Consultant in
inborn errors of metabolism who explained the test results and
the diagnosis. Blood spots were taken for repeat acylcarnitines
and also for mutation analysis. A urine specimen was collected for
urinary organic acids. The result of the repeat acylcarnitine,
available the same day, confirmed the diagnosis. She was then
reviewed by the specialist dietician who provided guidance
regarding fasting times and an emergency regime. A follow-up
appointment was made for a month’s time and the baby’s local
hospital was contacted and provided with a copy of the emer-
gency regime should she present to them.
Box 2
SYMPOSIUM: INBORN ERRORS OF METABOLISM
without screening for MCADD should also be investigated. Occa-
sionally parents have also been found to be affected demonstrating
that survival into adulthood without severe illness is possible.
Prognosis and explanation e Box 2 highlights the process
followingdiagnosis bynewborn screening andBox3 thekeypoints to
Key points to convey to parents
C The outcome for a child with MCADD deficiency is excellent
once the diagnosis is made. Growth, development and general
health are unaffected.
C When well no special treatment is required; a normal healthy
diet should be given & no specific medication is necessary.
C The recommended age related fasting times for children with
MCADD when well, err on the side of caution and do not need
to be shortened.
C The emergency regimen must be followed during periods of
illness or poor feeding to prevent complications.
C Cot death, without any preceding illness, is not caused by
MCADD.
C Parents should contact the specialist team if they have any
concerns regarding their child.
C MCADD is a genetic disorder with a recurrence risk for further
children.
Box 3
PAEDIATRICS AND CHILD HEALTH 21:2 93
convey to the parents. Not surprisingly parental anxiety relating to
their child’s management is common and families will need consid-
erablesupport includingdirect telephoneaccess to thespecialist team.
Follow-up e children with MCADD should remain under
follow-up with a specialist metabolic Paediatrician and Dieti-
cian with regular reviews in early childhood. Once middle
childhood is reached, yearly reviews are usually sufficient.
Parents should be allowed direct access to the local hospital’s
paediatric service so that lengthy waits in emergency depart-
ments (where there may be little awareness of the necessity of
rapid treatment) are avoided. Copies of the emergency regimen
should be provided to all relevant health professionals including
the GP and local Paediatrician. Once the child reaches adoles-
cence and is more independent as a person ‘Medic-alert’
bracelets are indicated.
Funding
None. A
FURTHER READING
British Inherited Metabolic Disease Group. Available at: http://www.
bimdg.org.uk.
Clarke JTR. A clinical guide to inherited metabolic disease. Cambridge:
Cambridge University Press, 2007.
UK newborn screening programme centre. Available at: http://www.
newbornbloodspot.screening.nhs.uk.
Practice points
C Children with MCADD are at significant risk of encephalopathy
during periods of fasting stress, particularly associated with
intercurrent infection.
C A high calorie emergency dietary regimen is given when
patients are unwell to prevent clinical deterioration.
C Oral rehydration solutions do not contain sufficient glucose to
prevent illness in MCADD.
C Intravenous treatment should be started immediately if the
emergency regime is not tolerated.
C When children are well no treatment is required although
periods without food should be limited, this depending on age
(Table 3).
C Hypoglycaemia should not be relied upon as a marker of early
decompensation or impending encephalopathy.
� 2010 Published by Elsevier Ltd.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
HyperlipidaemiaBorunendra N Datta
Duncan S Cole
Graham J Shortland
AbstractAssessment of hyperlipidaemia in children is important to prevent cardio-
vascular disease later in life. Secondary causes of hyperlipidaemia should
always be considered during clinical assessment. There are several
primary causes of primary hyperlipidaemia, of which familial hypercholes-
terolaemia (FH) is the most important. Diagnosis of FH is by use of the
Simon Broome criteria and genetic diagnosis can be helpful, particularly
in children. DNA diagnostics also facilitate cascade testing, which is
now recognized as an important means of identifying individuals with
FH. Several classes of drugs are used to treat hyperlipidaemia in children,
but the statins are most commonly used. They are effective and safe to
use in older children.
Keywords child; genetic testing; hydroxymethylglutaryl-CoA reductase
inhibitors; hyperlipidaemias; hyperlipoproteinaemia type II
Introduction
Cardiovascular disease remains the commonest cause of
mortality and morbidity in the United Kingdom (UK). Treatment
of lipid disorders in adults has had a significant impact in
reducing the overall burden of cardiovascular disease, particu-
larly in individuals who have sustained a cardiovascular event
such as myocardial infarction or stroke (secondary prevention).
There is increasing focus on primary prevention of cardiovas-
cular disease, including consideration of the cardiovascular
health of children. It is lifetime exposure to vascular risk factors,
such as low-density lipoprotein cholesterol (LDL-C), that appears
to be of importance. This is particularly so for monogenic causes
of hyperlipidaemia, the archetype of which is familial hyper-
cholesterolaemia (FH) where an affected individual is exposed to
high levels of LDL-C from birth. Secondary causes of hyper-
lipidaemia are of increasing relevance in childhood due to the
burgeoning obesity epidemic and its association with type 2
Borunendra N Datta MB BCh MD MRCP FRCPath is an SpR in Chemical
Pathology and Metabolic Medicine at the University Hospital of Wales,
Heath Park, Cardiff CF14 4XW, UK. Conflicts of interest: none.
Duncan S Cole BSc MB BCh PhD MRCP FRCPath is an SpR in Chemical
Pathology and Metabolic Medicine at the University Hospital of Wales,
Heath Park, Cardiff CF14 4XW, UK. Conflicts of interest: none.
Graham J Shortland BM DCH FRCPCH FRCP is a Consultant Paediatrician
with Special Interest in Inherited Metabolic Disease at the University
Hospital of Wales, Heath Park, Cardiff CF14 4XW, UK. Conflicts of
interest: none.
PAEDIATRICS AND CHILD HEALTH 21:2 94
diabetes mellitus. In this review we provide an overview of lipid
metabolism and discuss both secondary and primary causes of
dyslipidaemia in childhood, with a particular focus upon FH.
Current treatment options will also be appraised.
Overview of lipid metabolism
Two pathways of lipid metabolism are recognized: the exoge-
nous and endogenous pathways (see Figure 1). The exogenous
pathway functions to distribute triglycerides and cholesterol
absorbed from the diet to peripheral tissues for use or storage. It
is characterized by the formation of chylomicrons, large lipo-
proteins that are particularly triglyceride-rich. Once deplete of
triglycerides the particle is known as the chylomicron remnant,
which is cleared by the liver.
The endogenous pathway functions in the fasted state to
deliver lipids to peripheral tissues. This is achieved by the
formation of very low-density lipoprotein (VLDL) in the liver,
a triglyceride-rich lipoprotein which also contains cholesterol.
Triglycerides are delivered peripherally and the particle reduces
in size and increases in density; these are sequentially known as
intermediate density lipoprotein (IDL) and finally LDL. These
contain proportionally more cholesterol, and LDL in particular
delivers cholesterol to tissues. Any that remains is cleared by the
liver via the LDL-receptor (LDL-R); this is the defective step in
familial hypercholesterolaemia. The sequence of events in LDL-R
synthesis and in binding and processing of LDL is shown in
Figure 2.
A further pathway also exists, known as reverse cholesterol
transport. High-density lipoprotein (HDL) is the major lipopro-
tein involved. It is produced by the liver in a cholesterol deplete
state, and acquires cholesterol from tissues. A complex interplay
then occurs between HDL and other lipoproteins, such that
excess cholesterol is returned to the liver via HDL, and apoli-
poproteins are re-distributed.
Figure 1 Exogenous and endogenous cholesterol pathways. Triglyceride
(TG)-rich particles from the gut (chylomicrons, CM) and liver (very low-
density lipoproteins, VLDL) release fatty acids (FA) via the action of
lipoprotein lipase on TGs. Cholesterol is released to peripheral tissues
from LDL particles.
� 2010 Elsevier Ltd. All rights reserved.
Figure 2 LDL-receptor synthesis and recycling. The LDL-receptor is
synthesized and trafficked to the cell surface ready to bind ApoB on LDL.
Once bound, the LDL/LDL-receptor complex is internalized and fusion with
a lysosome occurs. This releases the LDL and digests it, resulting in free
cholesterol efflux and recycling of the receptor back to the surface.
Mutations resulting in FH can occur at numerous points along this
pathway, all resulting in inadequate clearance of LDL from the circulation.
Laboratory investigations for the assessment ofhyperlipidaemia
Investigation
Total cholesterol, LDL-C, HDL-C, triglycerides
Renal function and urine dipstick
Bilirubin, albumin, ALP, ALT or AST
Fasting plasma glucose
Thyroid function test
LDL-C ¼ low-density lipoprotein cholesterol; HDL-C ¼ high-density lipopro-
tein cholesterol; ALP ¼ alkaline phosphatase; ALT ¼ alanine aminotrans-
ferase; AST ¼ aspartate aminotransferase.
Table 1
SYMPOSIUM: INBORN ERRORS OF METABOLISM
It is important to note that when cholesterol is measured by
a clinical laboratory, it is derived from all the lipoproteins
mentioned above. HDL cholesterol measurements isolate the
cholesterol specifically from this fraction, but LDL cholesterol
concentration is often a calculated estimate based on an
assumption of the ratio of triglyceride to cholesterol in VLDL.
This may not always be applicable, for example when chylomi-
crons are present in the non-fasted state, or where IDL is the
predominant non-HDL/non-LDL fraction.
Cholesterol concentrations also vary with age. In children
they show a slight rise until age 10e11, and then dip during
puberty before rising to adult levels. A steady rise then occurs
throughout adulthood.
Cardiovascular risk in children
The assessment of global cardiovascular risk is well established
in adults. Calculation of cardiovascular risk is commonly used to
target therapies for primary prevention. Several tools may be
used, many of which use data from the Framingham study,
a long term ongoing study of cardiovascular risk. These take into
account variables such as total cholesterol, HDL-C, age and
systolic blood pressure. The output from such risk factor calcu-
lators is usually expressed as percentage risk of developing
cardiovascular disease over a 10-year period. There is limited
data to support the use of these tools in paediatric practice and
the cardiovascular risk of a child over the next 10 years will
always be low due to the influence of young age. Post-mortem
studies, such as the PDAY (Pathobiological Determinants of
Atherosclerosis in Youth) study demonstrate that atherosclerosis,
with the formation of fatty streaks, begins in childhood, and
calculation of lifetime cardiovascular risk may therefore be more
applicable in the paediatric population. However, such calcula-
tors for children are not yet in widespread use. The American
Academy of Paediatrics therefore recommends assessment of
lipid status in overweight and obese children, and in those with
PAEDIATRICS AND CHILD HEALTH 21:2 95
diabetes mellitus or hypertension as well as smokers and those
with a family history of dyslipidaemia or premature cardiovas-
cular disease. For individuals with FH the use of cardiovascular
risk assessment tools based upon Framingham data are inap-
propriate as they tend to underestimate cardiovascular risk in
untreated FH.
Secondary causes of hyperlipidaemia
When interpreting a lipid profile it is important to recall that
a number of conditions can be associated with dyslipidaemia.
Treatment of the underlying disease will often completely correct
this. Several biochemical tests should therefore be requested as
part of the assessment of a lipid disorder (Table 1).
Diabetes mellitus
Type 1 and type 2 diabetes mellitus are both associated with an
increased lifetime risk of cardiovascular disease. However, well-
controlled type 1 diabetes mellitus is not typically associated
with significant dyslipidaemia. The obesity epidemic has driven
the rate of development of type 2 diabetes mellitus, with
increasing numbers of cases diagnosed in childhood. Type 2
diabetes mellitus is often associated with characteristic lipid
abnormalities, typically an increase in total cholesterol and
triglycerides and a reduction in HDL-C. There is currently no
evidence to support lipid-lowering therapy for the vast majority
of children with diabetes mellitus. However, given the increased
lifetime cardiovascular risk attributable to the disease, treatment
should be considered particularly when there are multiple risk
factors present, such as obesity, smoking and hypertension.
Thyroid disease
Untreated hypothyroidism may be associated with increased total
and LDL cholesterol. This is probably due to decreased receptor-
mediated LDL catabolism. Treatment of the hypothyroidism
almost invariably results in resolution of hypercholesterolaemia.
Use of statins in untreated hypothyroidism is associated with an
increased risk of myopathy.
Renal disease
Nephrotic syndrome is associated with increased total and LDL-C
and to a lesser extent reduction in HDL-C. The degree of dysli-
pidaemia appears to be inversely related to the serum albumin
� 2010 Elsevier Ltd. All rights reserved.
Effect of drug therapy commonly associated with lipidabnormalities
Drug Triglycerides LDL HDL
SYMPOSIUM: INBORN ERRORS OF METABOLISM
concentration. An increase in hepatic VLDL production subse-
quently results in an increase in circulating LDL-C. Evaluation of
urinary protein is easily overlooked in a patient who is referred
for evaluation of FH and should be a mandatory part of the
evaluation.
cholesterol cholesterol
Thiazides [ [ e
Liver diseaseb blockers [ e Y
Oestrogens [ e [
Retinoic acid derivatives [ e e
Protease inhibitors [ [ Y
Ciclosporin e [ e
Obstructive jaundice is associated with an increase in total
cholesterol due to an increase in lipoprotein particles similar to
LDL. Hepatocellular disease is more often associated with
hypertriglyceridaemia. The latter is a predominant feature of
non-alcoholic fatty liver disease which has a strong association
with obesity and insulin resistance.
Table 3
AlcoholExcess alcohol ingestion may be associated with hyper-
triglyceridaemia, because of increased hepatic triglyceride produc-
tion, which subsequently leads to an increase in hepatic VLDL
secretion. Enquiry regarding alcohol consumption is therefore
important in the assessment of dyslipidaemia in older children.
Anorexia nervosa
Hypercholesterolaemia is a recognized feature of eating disor-
ders. It appears to be particularly associated with the bulimic
subtype of anorexia nervosa. Multiple mechanisms are respon-
sible, including endocrine changes secondary to loss of adipose
tissue, and increased absorption of dietary cholesterol during
high-fat binging episodes. The relevance of this to cardiovascular
risk is not clear, and tackling dyslipidaemia as an isolated issue is
usually not productive unless there are other concerns with
regards cardiovascular risk or there is a family history of FH.
Drugs causing hyperlipidaemia
Several classes of drugs used in paediatric practice may be
associated with dyslipidaemia (Table 3). In some cases it may be
possible to switch to an alternative drug, for example agents used
for the treatment of hypertension. If a drug which causes
Simon Broome register criteria for diagnosis of familial hype
Lipid criteria
Definite FH
Age <16 years: total cholesterol >6.7 mmol/l or LDL-C >4.0 mmol/l
Age >16 years: total cholesterol >7.5 mmol/l or LDL-C >4.9 mmol/l
Possible FH
Age <16 years: total cholesterol >6.7 mmol/l or LDL-C >4.0 mmol/l
Age >16 years: total cholesterol >7.5 mmol/l or LDL-C >4.9 mmol/l
FH ¼ familial hypercholesterolaemia; LDL-C ¼ low-density lipoprotein cholesterol; LD
tase subtilisin kexin type 9.
Table 2
PAEDIATRICS AND CHILD HEALTH 21:2 96
dyslipidaemia is not likely to be used for long term therapy, such
as a course of an oral retinoic acid derivative, a transient dysli-
pidaemia is likely to be clinically acceptable. Otherwise an
assessment of overall cardiovascular risk should be made, to
help decide if treatment of the dyslipidaemia is required.
Primary causes of hyperlipidaemia
Familial hypercholesterolaemia
Autosomal co-dominant FH is the most common monogenic
cause of coronary heart disease (CHD). Most cases are caused by
mutations in the LDL-R which results in high circulating LDL-C.
The estimated prevalence of heterozygous FH is 1 in 500 in
Europe and North America. Untreated it carries a risk of
premature coronary disease of >50% in men and >30% in
women by the age of 60 years.
Homozygous FH has an estimated prevalence of 1 in 1,000,000
and is associated with circulating LDL-C levels in excess of 10
mmol/l. CHD in homozygous FH presents from the second decade
of life. The risk of cardiovascular mortality andmorbidity is linked
to extensive atherogenesis affecting the proximal aorta, aortic
rcholesterolaemia
Other criteria required for diagnosis
Tendon xanthomata in patient or in first degree relative
(parent, sibling or child) or in second degree relative
(grandparent, uncle or aunt)
OR
DNA evidence of a mutation in LDL-R, apolipoprotein
B-100 or PCSK9 genes
At least one of the following:
Family history of myocardial infarction in first degree relative aged
<60 years or second degree relative aged <50 years
OR
Family history of raised total cholesterol: >7.5 mmol/l in adult first
or second degree relative or >6.7 mmol/l in child or sibling aged
<16 years
L-R ¼ low-density lipoprotein cholesterol receptor; PCSK9 ¼ proprotein conver-
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
valve and coronary arteries. Florid physical signs are often
present, such as tendon and subcutaneous xanthomata.
Diagnosis of familial hypercholesterolaemia: the diagnosis of
FH involves a personal and family history, physical examination,
measuring total and low-density lipoprotein cholesterol (LDL-C)
in serum and the use of DNA diagnostics. In the UK the Simon
Broome criteria (Table 2) are used as they were developed using
a UK population and are straightforward to employ in the clinic.
However all clinical diagnostic criteria lack specificity and
sensitivity, particularly in less severe presentations when
cholesterol concentrations may not reach the diagnostic thresh-
olds. This is a particular issue in children and younger people
due to the variation of cholesterol concentrations with age, and
diagnostic physical stigmata, particularly tendon xanthomata,
are often absent in children. For these reasons there is an
increasing role for a DNA diagnosis in suspected FH in paediatric
practice.
Genetics of familial hypercholesterolaemia: FH is most
commonly caused by mutations in the LDL-receptor gene, with
a smaller number of cases due to mutations in the Apo B-100 and
PCSK9 genes. There is a higher risk of CHD in individuals with an
LDL-R mutation, compared to those who are mutation negative.
Mutations may be indentified in up to 90% of individuals with
‘definite’ FH (with tendon xanthomata) and genetic testing in
patients with ‘possible’ FH can help clarify the diagnosis. Current
National Institute for Health and Clinical Excellence Clinical
Guidelines support early identification of FH in children from age
10 years and a DNA diagnosis can provide conclusive evidence of
a diagnosis to parents and their doctors. However, the absence of
a detectable DNA mutation does not exclude the diagnosis of FH
and an individual with a clinical diagnosis of FH who does not
have a demonstrable DNA mutation should still be considered at
high risk and treated accordingly.
Cascade testing for familial hypercholesterolaemia: in the UK
it is estimated that 85% of the estimated 120,000 people who are
affected by FH have not been diagnosed. Cascade testing is the
preferred strategy for identifying these individuals. The most
efficient and cost effective approach is to use DNA testing for
those families with a known mutation or cholesterol testing in
those families in whom a mutation cannot be found. Cascade
testing commenced across Wales in 2010 with extension to the
rest of UK anticipated in the next few years. One consequence of
this approach is that there will be an increase in the number of
children and young people identified with FH who will need
advice and treatment.
Polygenic hypercholesterolaemia
Polygenic hypercholesterolaemia is muchmore common than FH.
An increase in total cholesterol and LDL-C is seen, but clinically the
differentiation from FH may not be clear. DNA testing can be
particularly helpful in this situation. The genetics of this condition
are not as well understood as for FH. Several genes are likely to be
important as well as lifestyle factors, such as obesity and poor diet.
Polygenic hypercholesterolaemia is more commonly identified in
adults and the risk of premature CHD is much lower than for FH
with a documented DNA mutation.
PAEDIATRICS AND CHILD HEALTH 21:2 97
Familial combined hyperlipidaemia
Familial Combined Hyperlipidaemia (FCHL) is an important
disorder, but is much less clearly defined than FH. It is likely that
several genes are responsible and lifestyle factors may also be
important. Typically the total and LDL-C are elevated as well as
serum triglycerides, although there does seem to be significant
heterogeneity in the lipid profiles of families with FCHL. The
abnormal lipid profile probably occurs due to overproduction of
VLDL.
Hypertriglyceridaemia
Hypertriglyceridaemia may be seen in childhood, usually due to
a precipitating factor in a susceptible individual (see Secondary
causes of hyperlipidaemia). Genetic forms also exist, such as
the rare familial lipoprotein lipase deficiency, which may result
in severe hypertriglyceridaemia. Presentation with this disorder
may be with eruptive xanthomata or acute abdominal pain,
which may be recurrent. Acute pancreatitis may occur when the
triglycerides exceed 10e15 mmol/l, and may occasionally exceed
100 mmol/l. In childhood this results from the failure to clear
chylomicrons, although in the teenage and adult years VLDL may
also accumulate. Treatment for a primary hypertriglyceridaemia
thus focuses on restriction of fat intake.
Treatment
Lifestyle interventions
Lifestyle therapies are an important component in the treatment
of hyperlipidaemia and involve avoidance of smoking and die-
tary and exercise interventions. Such interventions are important
for general long-term cardiovascular health and the prevention
and treatment of obesity. Lifestyle intervention alone is usually
not effective for the prevention of cardiovascular disease in
inherited dyslipidaemias. The role of nutritional supplements,
containing plant stanols and sterols is not clear in children, but
beneficial effects appear to be similar to those seen in adults.
Drug therapy
Statins: theyare themost commonlyusedclassofdrugsused to treat
hyperlipidaemia in both children and adults. They work through
inhibiting the rate determining step of the cholesterol biosynthesis,
HMG-CoA reductase, and effectively reduce total and LDL choles-
terol. They have limited effects upon triglyceride and HDL-C
metabolism. There are few randomized placebo controlled trials of
statins in paediatric FH, but a wealth of data has confirmed the
beneficial effects of statins in the reduction of cardiovascular
mortality and morbidity in non-FH adults. There are no outcome
studies in children and most have used surrogate markers, such as
measures of endothelial function and carotid intima media thick-
ness. These have indicated an improvement in surrogate markers
with statins in theFHpopulation. Previous concerns that statinsmay
not be safe in children appear to be unfounded, as data now confirm
that statins do not have detrimental effects upon growth and
development and are generally well tolerated. Therapy should be
considered in an individual child based upon LDL-C concentrations
and the age of onset of cardiovascular disease in family members.
Treatment with a statin should be considered in FH from the age of
10. In the UK currently Atorvastatin is licensed in children over the
age of 10 years up to a dose of 20 mg per day and Pravastatin is
� 2010 Elsevier Ltd. All rights reserved.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
licensed at a dose of 10e20 mg per day in children aged 8e14 years
and up to 40 mg in older children.
Other drug therapy: Ezetemibe decreases intestinal absorption
of cholesterol and may be used in children. Its main use is in
combination therapy with statins, in particular for children with
homozygous FH. It can also be used in monotherapy, for instance
if statin therapy is not tolerated.
Fibrates reduce hepatic triglyceride production and peripheral
lipolysis and have been used in children. Their main use is in the
treatment of hypertriglyceridaemia and they have a limited effect
in reducing LDL-C.
Bile acid sequestrants and nicotinic acid are also licensed for
use in hyperlipidaemia, but are not widely used in children.
LDL apheresis
LDL apheresis is a treatment similar to renal dialysis. Patients
usually attend fortnightly. LDL cholesterol is removed from the
patient and absorbed onto a specific LDL absorption column and
blood then returned to the patient. This invasive procedure
effectively reduces LDL cholesterol in conjunction with drug
therapy and its use should be considered in all children with
homozygous FH.
Practice points
General issuesC Assessment of serum lipids should be carried out in children
with a family history of premature cardiovascular disease or
dyslipidaemia
C Assessment of serum lipids may also be useful in children with
other cardiovascular risk factors
C Screening investigations should be used to exclude secondary
causes of dyslipidaemia
C Familial Hypercholesterolaemia is the commonest inherited
monogenic cause of premature cardiovascular disease
C Statins are effective and safe in children aged 10 years or
older
The majority of children and young people are currently
managed in specialist centres for inherited metabolic disease
where advice can be obtained. With cascade testing and an
increase in the number of children and young people identified
with FH new strategies for secondary care will need to be
considered to advise and treat these patients. A
FURTHER READING
Arambepola C, Farmer AJ, Perera R, Neil HAW. Statin treatment for children
and adolescents with heterozygous familial hypercholesterolaemia:
a systematic review and meta-analysis. Atherosclerosis 2007; 195:
339e47.
PAEDIATRICS AND CHILD HEALTH 21:2 98
Daniels SR. Greer FR and the Committee on Nutrition. Lipid screening and
cardiovascular health in childhood. Pediatrics 2008; 122: 198e208.
Datta BN, McDowell IFW, Rees JAE. Integrating provision of specialist lipid
services with cascade testing for familial hypercholesterolaemia. Curr
Opin Lipidol 2010; 21: 366e71.
Durrington PN. Hyperlipidaemia diagnosis and management. 3rd Edn.
London: Hodder Arnold, 2007.
National Institute for Health and Clinical Excellence. Clinical guidelines
and evidence review for familial hypercholesterolaemia: the identifi-
cation and management of adults with familial hypercholesterolaemia.
Clinical Guidelines 71; 2008.
Pathobiological Determinants of Atherosclerosis in Youth Research Group.
Relationship of atherosclerosis in young men to serum lipoprotein
cholesterol concentrations and smoking. JAMA 1990; 264: 3018e24.
Umans-Eckenhausen MAW, Defesche JC, Sijbrands EJG, Scheerder RLJM,
Kastelein JJP. Review of first 5 years of screening for familial hyper-
cholesterolaemia in the Netherlands. Lancet 2001; 357: 165e8.
Wierzbicki AS, Viljoen A. Hyperlipidaemia in paediatric patients. The role
of lipid-lowering therapy in clinical practice. Drug Saf 2010; 33:
115e25.
� 2010 Elsevier Ltd. All rights reserved.
SELF-ASSESSMENT
Self-assessment
Questions
Case 1
A 10-day-old baby girl was admitted with poor feeding, leth-
ALT 49 U/litre (1e50)
GGT 38 U/litre (0e78)
Protein 50 g/litre (60e80)
Albumin 35 g/litre (35e50)
PT 30.1 s (11.4e14.3)
APTT 82.3 s (25.2e33.5)
Fibrinogen 1.4 g/litre (1.9e4.3)
CSF microscopy Negative for infection
CSF glucose 2.2 mmol/litre
CSF protein 1.2 g/litre
Venous gas pH 7.38, pO2 4.3 kPa, pCO2 6.0 kPa,
argy and weight loss (Wt 3.01 kg; Birth wt 3.42 kg). She was
born at term, breast fed initially but formula fed from day 3.
Shewas apyrexial, warm andwell perfused but jaundiced.
Respiratory rate was 36/min and respiratory system exami-
nation was normal. Abdominal examination revealed soft
abdomen with a 3 cm liver edge palpable and cardiovascular
examination revealed the presence of a systolic murmur, but
no other abnormal findings. The peripheral pulses as well as
oxygen saturations were normal in all 4 limbs.
Blood results
Hb 16.4 g/dL (12.1e16.3)
WCC 10�109/litre (5e19.5)
Neutrophils 0.7�109/litre (2e9)
Lymphocytes 7.7�109/litre (3.5e8.5)
Platelet count 153�109/litre (150e400)
Na 133 mmol/litre (133e146)
K 5.2 mmol/litre (3.5e5.3)
Urea 2.4 mmol/litre (2.5e7.8)
Creatinine 38 mmol/litre (0e39)
CRP <5 mg/litre (<5)
Total bilirubin 379 mmol/litre (1e17)
Direct bilirubin 38 mmol/litre (0e8)
ALP 1028 U/litre (60e350)
BE e5.1 mmol/litre
Glucose 3.4 mmol/litre
Lactate 1.0 mmol/litre
Ammonia 61 umol/litre (11.2e35.4)
Ranjana Kanekal MB ChB is a Foundation year 2 Trainee in the
Department of Paediatrics at James Cook University Hospital,
Middlesbrough, UK.
Susan M George MB BS MSc PhD is a Specialist Trainee in the
Department of Paediatrics at James Cook University Hospital,
Middlesbrough, UK.
Ramesh B Kumar MB BS MD MRCPCH is a Consultant Paediatrician in the
Department of Paediatrics at James Cook University Hospital,
Middlesbrough, UK.
Maeve O’Sullivan MB ChB MRCPCH PhD is a Consultant Paediatrician in
the Department of Paediatrics at James Cook University Hospital,
Middlesbrough, UK.
Mark Burns MB ChB MRCPCH is a Consultant Paediatrician in the
Department of Paediatrics at James Cook University Hospital,
Middlesbrough, UK.
PAEDIATRICS AND CHILD HEALTH 21:2 99
1. Which among the following is the most important
diagnosis to consider in this baby? Choose ONE answer
a) Neonatal sepsis
b) Metabolic illness
c) Congenital cardiac disease
d) Insufficient milk intake
She was commenced on IV broad spectrum antibiotics
(Benzylpenicillin and Gentamicin, later changed to Cefo-
taxime) and acyclovir (added to cover potential viral
infection). She was kept on 60 ml/kg/day of IV fluids (and
small amounts of bottle feeds).
At 48 h, the blood culture grew E. coli but CSF culture was
reported negative. Coagulopathy improved with adminis-
tration of fresh frozen plasma and vitamin K.
She completed 14 days of IV antibiotics, and tolerated
feeds well once the formula was changed. She improved
with the above management and underwent further inves-
tigations which identified the diagnosis.
2. Which of the following metabolic illnesses is most likely
in this child? Choose ONE answer
a) Mitochondrial disease
b) Galactosaemia
c) Neonatal haemochromatosis
d) Lysosomal storage disease
e) Fructose intolerance
3. Which specific investigation would confirm this diag-
nosis? Choose ONE answer
a) Galactose 1 phosphate uridyl transferase (Gal 1 PUT)
level
b) Muscle biopsy
c) Liver biopsy
d) MRI brain
e) Urinary organic acids
� 2010 Published by Elsevier Ltd.
SELF-ASSESSMENT
4. What are the most important management strategies
with this condition? Choose THREE answers
a) Regular paediatric follow-up
b) Pubertal development and fertility assessment
c) Prophylactic antibiotics
d) Annual ophthalmology review
e) Lactose free diet
f) Anti-epileptic medication
g) Fructose free diet
h) Cardiology assessment
i) Desferrioxamine
Case 2
A 6-month-old boy of African origin presented to A&E
following third episode of afebrile seizures within 1 week.
He was born at term by emergency caesarean section for
foetal distress. There were no antenatal or postnatal
concerns. The baby was exclusively breast fed for first 4
months. At the time of presentation, his diet consisted of
breast milk, mashed potatoes and carrots as well as
confectionaries.
Seizures lasted 2e3 min each, with increased tone
involving the whole body, during which he remained
unresponsive. There was associated up-rolling of eyes and
frothing at the mouth. No clonic movements were reported.
There was spontaneous recovery in each case after which
he became drowsy and slept for 1e2 h.
Examination revealed a thriving child who was also
neuro-developmentally normal.
Figure 1
PAEDIATRICS AND CHILD HEALTH 21:2 100
Blood investigations
FBC Normal
Urea & electrolytes
NormalMagnesium
0.98 mmol/litre (0.74e1.11)Ferritin
38 mg/litre (41e400)ALP
908 units (75e255)Serum calcium
1.65 mmol/litre (2.1e2.6)Phosphate
1.15 mmol/litre (1.22e2.47)PTH
294.2 ng/litre (12e72)1. What does this X-ray show (Figure 1)? Choose ONE
answer
a) Normal X-ray
b) Osteoporosis
c) Cupping and fraying of the ends of long bones
d) Skeletal dysplasia
2. What is the most likely underlying clinical diagnosis in
this child? Choose ONE answer
a) Nutritional rickets
b) Epilepsy
c) Osteogenesis imperfecta
d) Pseudo-hypoparathyroidism
3. What are the key components in the management of this
child? Choose THREE answers
a) Oral vitamin D administration
b) IM vitamin D administration
c) Anti-epileptic medication
d) Health education regarding diet
e) IV calcium gluconate
f) Oral calcium supplements
g) Phosphate supplements
h) Magnesium supplements
i) All of the above
Case 3
A healthy term baby girl was born with a large birth mark
involving the right side of her face. This was deep red in
colour, macular and involving the eyelid, cheek & forehead.
Newborn examination was normal.
She remained well until 5 months of age when she first
presented with seizures. Her seizures involved the left side
of the face & limbs, initially starting with facial twitching
movements, progressing to have tonic clonic movements
which started with left upper limb and subsequently
involved all four limbs. The duration and frequency
of seizures were variable with as many as five seizures in
a 24-h period.
1. What is the most likely clinical diagnosis based on the
above history? Choose ONE answer
a) Epilepsy
b) SturgeeWeber syndrome
c) Cerebral palsy
d) Congenital vascular malformation
e) Tuberous sclerosis
� 2010 Published by Elsevier Ltd.
Figure 2
SELF-ASSESSMENT
2. What does the above MRI scan show (Figure 2)? Choose
ONE answer
a) Normal scan
b) Vascular malformation on the right side
c) Decreased in size & calcifications in the right
hemisphere
d) Right MCA territory infarction
3. What are the associated complications commonly seen
with this condition? Choose ONE answer
a) Learning difficulties
b) Glaucoma
c) Cutaneous vascular malformations
d) Intracranial & ophthalmic tubers
e) Renal involvement
4. What are the most important management strategies in
this condition? Choose THREE answers
a) Anti-epileptic medication
b) Hemispherectomy
c) Regular ophthalmology review & intraocular pressure
monitoring
d) Physiotherapy
e) Laser treatment of the facial lesion
f) Occupational therapy
g) Long term antibiotics
h) Oral anticoagulants
i) Regular monitoring of renal function
j) All of the above
Answers
Case 1
1. a) Sepsis
In a neonate presenting in this manner, three main
diagnoses must be considered e sepsis, congenital cardiac
diseases and metabolic illnesses. Deranged coagulation and
PAEDIATRICS AND CHILD HEALTH 21:2 101
raised liver enzymes with mild jaundice in a neonate must
make one suspect neonatal sepsis. A metabolic illness is
very likely in this child suggested by the mode of presen-
tation, but needs further investigations to confirm this.
Normal cardiovascular examination makes congenital
cardiac diseases less likely. Poor milk intake is often
secondary to the underlying problem, leading to hypo-
volaemia. Poor feeding due to poor lactation or feeding
techniques can cause weight loss and hypovolaemia. Such
neonates often present with significant hypernatraemia and
raised serum & urinary osmolality.
2. b) Galactosaemia
Classical galactosaemia is an autosomal recessive
disorder of galactose metabolism caused by the deficiency
of Gal 1 PUT enzyme, with an incidence of 1/23e44,000.
Majority presents in neonatal period after ingestion of
galactose (derived from lactose in milk), with poor feeding
& feed intolerance, jaundice, hepatosplenomegaly, hepato-
cellular insufficiency, hypoglycaemia, muscle hypotonia,
cataracts and sepsis. E coli sepsis is seen more frequently in
these babies.
Mitochondrial diseases have variable presentations with
some conditions presenting early with significant metabolic
acidosis, collapse and sudden infant death.Many present later
with hypotonia, developmental delay and neurological prob-
lems. Neonatal haemochromatosis is a fatal, progressive
illness which often presents within the first few days of life,
characterized by hepatomegaly, hypoglycemia, coagulopathy
(refractory to Vitamin K therapy) hypoalbuminaemia, hyper-
ferritinaemia and hyperbilirubinaemia. Lysosomal storage
disorders (e.g.Gaucher’s) present later in infancywithhepato-
splenomegaly, psychomotor retardation and evidence of bone
marrow infiltration. Fructose intolerance can present with
very similar clinical features following introduction of fruits
and fruit juices. Age at presentation, absence of metabolic
acidosis and coagulopathy which responded to treatment
makes the above diagnoses less likely.
3. a) Galactose 1 phosphate uridyl transferase (Gal-1-PUT)
Gal-1-PUT is the enzyme that is deficient in
galactosaemia.
In view of the neonatal liver disease, coagulopathy and
E. coli sepsis, this baby was investigated for Gal-1-PUT
deficiency by measuring the enzyme activity in erythrocytes
(Patient <0.5; Normal: 18e28) and a diagnosis of classical
galactosemia was made. This was later confirmed with
DNA mutation analysis.
Classical galactosaemia is part of newborn screening
programmes of many countries.
4. a,d,e) Regular paediatric follow-up, annual ophthal-
mology review, lactose free diet
Successful management of galactosaemia requires
appropriate dietary input. A galactose-restricted diet is
advised. Lactose free milk (e.g. Wysoy) is advised in
neonatal period. After this, lactose-free diet without
restriction of galactose containing fruits and vegetables is
� 2010 Published by Elsevier Ltd.
SELF-ASSESSMENT
recommended in most countries. Paediatric follow up with
a team that is familiar with management of galactosaemia is
required. They also require written plan for management of
acute illnesses. Patients are advised to access hospital
services early, commence IV fluids and supplementary
feeding regime in order to prevent crises.
Long-term complications include mental retardation,
verbal dyspraxia, motor abnormalities and hypogonadic
hypogonadism. This is often seen in patients despite strict
diet and is thought to be due to endogenous galactose
production.
Couples with an affected child have a 25% chance of
having an affected child in each subsequent pregnancy.
FURTHER READING
Bosch AM. Classical galactosaemia revisited. J Inherit Metab Dis
2006; 29: 516e525.
Livingston VH, Willis CE, Abdel-Wareth LO, Thiessenn P, Lockitch G.
Neonatal hypernatremic dehydration associated with breast-
feeding malnutrition: a retrospective survey. Can Med Assoc J
2000; 162: 647e652.
Weblink: British InteritedMetabolic Disease Group. www.bimdg.org.uk.
Case 2
1. c) Cupping and fraying of the end of long bones
Widening of the metaphyseal ends of radius and ulna, as
well as cupping and fraying of these bones (see arrows in
Figure 3) noted. This is a pathognomonic feature of rickets.
Figure 3
PAEDIATRICS AND CHILD HEALTH 21:2 102
2. a) Nutritional rickets
Main sources of Vitamin D in children are foods such as
oily fish, butter & eggs, and ultraviolet irradiation of 7-
dehydrocholesterol in the skin. Dietary cholecalciferol
(Vitamin D3) is hydroxylated by liver to 25-hydroxy
cholecalciferol and then the kidneys to 1,25-dihydroxy
cholecalciferol (active form of vitamin D).
Biochemical features of nutritional rickets e low plasma
calcium, raised alkaline phosphatase & parathyroid
hormone, and decreased serum vitamin D levels e were
noted. The serum 25 OH Cholecalciferol level was 15 nmol/
litre (Normal: 40.4e168).
Radiological features of rickets include poor mineraliza-
tion of both flat & long bones, delayed development of the
epiphysis and metaphyseal changes at the growing ends of
long bones (concave, irregular margins are found together
with increased diameter e cupping, fraying & splaying).
Prominence of costochondral junctions causes ‘rachitic
rosary’. More significant abnormalities are seen in long
standing rickets. Seizures and tetany suggest hypocalcaemia.
In pseudo-hypoparathyroidism, serumphosphate is raised.
3. a,e,f) Oral Vitamin-D administration, IV calcium gluco-
nate, oral calcium supplementation
Oral Vitamin-D3 at a dose of 2000e6000 IU/day is
commenced as soon as the diagnosis is confirmed and
continued for at least 3 months. This should be followed by
daily Vitamin-D intake of 400 IU/day. IV calcium gluconate
is administered due to the presentation of hypocalcaemic
seizures. This child needs short-term oral calcium supple-
ments. With appropriate therapy, and introduction of a well
balanced diet containing adequate calcium & phosphorus,
nutritional rickets is a condition that is easily managed.
FURTHER READING
Balasubramanian S, Ganesh R. Vitamin D deficiency in exclusively
breast-fed infants. Ind J Med Res 2008; 127: 250e255.
Singh J, Moghal N, Pearce SHS, Cheetham TD. The investigation of
hypocalcaemia and rickets. Arch Dis Child Health 2003; 88:
403e407.
Case 3
1. a) SturgeeWeber syndrome
The presence of facial capillary haemangioma involving
the ophthalmic & maxillary branch distribution of trigem-
inal nerve, and focal onset of seizures with secondary
generalization points towards this diagnosis.
SturgeeWeber syndrome is the association of angiomas of
the leptomeninges and facial skin. Many children develop
seizures, developmental delay and glaucoma. Seizures often
develop in the 1st year of life, due to associated angiomas
involving the ipsilateral cerebral hemisphere. They are typi-
cally focal tonic-clonic, contralateral to the side of facial nae-
vus. There is associated shrinkage andneuronal cell loss of the
affected hemisphere. Hemiparesis and hemiplegia can occur,
which, along with recurrent seizures can lead to develop-
mental delay and disability.
� 2010 Published by Elsevier Ltd.
SELF-ASSESSMENT
2. c) Decreased size & calcifications in the right hemisphere
The ipsilateral hemisphere shows marked decrease in
size and evidence of calcification. Isolated MCA territory
infarction is unlikely to cause this degree of shrinking &
calcification of the hemisphere. Intracranial vascular mal-
formations leads to the presence of dilated blood vessels
(may have evidence of haemorrhage), which is not the most
prominent feature in this image.
3. b) Glaucoma
Glaucoma of the ipsilateral eye is a common association
in SturgeeWeber syndrome. Other associations include
learning difficulties, hemiplegia and protracted seizures
leading to disability.
PAEDIATRICS AND CHILD HEALTH 21:2 103
4. a,c,e) Anti-epileptic medication, regular ophthalmology
review & intra-ocular pressure monitoring, laser treat-
ment for the facial lesion
Management depends on the severity of symptoms.
Physiotherapy and occupational therapy may be required if
indicated. It is important to explain the diagnosis and
prognosis to the parents and review the child regularly.
Seizures can be difficult to manage and may require inser-
tion of vagal nerve stimulator or even surgical management
(hemispherectomy).
FURTHER READING
Nowak CB. The phacomatoses: dermatologic clues to neurologic
anomalies. Semin Paediatr Neurol 2007; 14: 140e149.
� 2010 Published by Elsevier Ltd.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
The investigation and theinitial management ofchildren with suspectedmetabolic diseasepresenting acutely*
J V Leonard
A A M Morris
AbstractInborn errors ofmetabolismare individually rare but somany have now been
described that the general paediatrician will encounter one from time to
time. For many, early treatment is important. Unfortunately most present
with non-specific symptoms and signs. It is therefore necessary to identify
and investigate those at high risk. Themost commonproblems are neurolog-
ical (including coma, seizures and stroke-like episodes), hypoglycaemia,
disorders of acidebase regulation, cardiomyopathy and acute liver disease.
Treatment should be started as soon as an inborn error is suspected.
Keywords acute liver failure; ataxia; cardiomyopathy; catabolism;
encephalopathy; hyperammonaemia; hypoglycaemia; metabolic acidosis;
respiratory alkalosis; seizures; stroke-like illness
Introduction
Inborn errors of metabolism are generally rare, although some
disorders are more common in genetically isolated populations.
Many inherited metabolic conditions are nowwell recognized and
they may present at almost any age from the newborn period into
adult life. Many disorders are now treatable and it is important to
recognize the underlying disorder at the earliest possible stage to
prevent permanent damage. Unfortunately however for most
disorders the early symptoms and signs are not specific so it is
necessary to try to identify those at high risk of having ametabolic
disorder.
* This chapter is a short introduction and cannot cover all situa-
tions. If in doubt, consult your local specialist metabolic centre.
Detailed and free instructions on the management of acute illness of
individual inborn errors of metabolism can be found on the British
Inherited Metabolic Disease Group (BIMDG) website http://www.
bimdg.org.uk/.
J V Leonard PhD FRCP FRCPCH is a Former Professor of Paediatric Metabolic
Disease at the UCL Institute of Child Health, and Consultant Paedia-
trician at Great Ormond Street Children’s Hospital, London, UK.
Conflicts of interest: none.
A A M Morris PhD FRCPCH is a Consultant in Paediatric Metabolic Medi-
cine at the Department of Genetic Medicine, St Mary’s Hospital, Oxford
Road, Manchester M13 9WL, UK. Conflicts of interest: none.
PAEDIATRICS AND CHILD HEALTH 21:2 51
History
The key to identifying those at high risk is the history, past,
family and that of the present illness.
Past history
After resuscitation it is important to inquire about any problems
before the present one such as previous episodes, episodic vom-
iting, developmental delay and episodes of drowsiness particularly
in the morning. Patients presenting with a severe acute encepha-
lopathy particularly may have had previous episodes, commonly
much milder precipitated by intercurrent infections or fasting.
Family history
Where there is a clear history of an affected sibling (more distant
relative in the case of X-linked disorders) or highly consanguin-
eous families, these leads must be followed up carefully. There
may be a history of undiagnosed death or unexplained illness
that may provide useful clues. Consanguinity, although relevant,
only increases the risk of an autosomal recessive disorder by
a modest percentage.
Modes of presentation
Although inborn errors may present in many different ways and at
almost any age, the common presentations can be simplified into
five categories: (1) neurological presentation including acute
encephalopathy, seizures, stroke-like illness and acute ataxia, (2)
hypoglycaemia, (3) disorders of acidebase regulation, (4)
cardiomyopathy and cardiac arrhythmias and (5) acute liver
disease. Metabolic disorders may also present at or soon after birth
with a number of different problems that include ascites/hydrops,
dysmorphic syndromes, seizures and severe hypotonia. Lists of
the causes of these problems can be found in Leonard and Morris
(2006).
Neurological presentation
Acute encephalopathy: a common presentation of inborn errors is
an acute encephalopathy but there are verymany causes of such an
illness. An acute metabolic encephalopathy may be very variable
ranging frommild to severe. Typically the symptoms are of gradual
onset, unless the patient has a convulsion. The early symptoms are
often drowsiness, lethargy, altered behaviour and unsteady gait.
These symptoms may fluctuate and then often somewhat unex-
pectedly the patients may deteriorate, becoming comatose. Treat-
ment is urgent and basic metabolic investigations should always be
done in any patient with an undiagnosed encephalopathy. An
episode may be precipitated by infection and fever but evidence of
these does not exclude the metabolic disorder.
The causes of metabolic encephalopathy and the investiga-
tions that are necessary to identify the majority of metabolic
disorders are summarized in Table 1.
Seizures: those disorders that may present with seizures with the
investigations are listed in Table 2.
Stroke-like episodes: the most common metabolic causes of
stroke-like episodes with the appropriate investigations are listed
in Table 3.
� 2010 Elsevier Ltd. All rights reserved.
Causes of acute metabolic encephalopathy
Causes Investigations
Hypoglycaemia
Hyperammonaemia including
urea cycle disordersa
Disorders of fatty acid
oxidation and ketogenesis
Amino acids disorders including
maple syrup urine disease
Organic acidaemias
Congenital lactic acidoses
Blood gases
Blood glucose
Blood lactate
Plasma electrolytes
& anion gap
Plasma ammonia
Plasma amino acids
Blood spot acyl carnitinesb,d
Liver-function tests
Plasma biotinidasec
Urine organic acids
a For a full list of inborn errors that cause hyperammonaemia see Table 20.2 in
Fernandes et al. (2006).b It can be difficult to identify carnitine transporter deficiency with blood spot
acyl carnitines as the values for free carnitine may be low but not very low.c Plasma biotinidase is included as this is a simple test and biotinidase deficiency
responds very well to treatment but this must be started at an early stage.d The results of any extended newborn screening investigations should be checked.
Table 1
Metabolic disorders that may present with seizures
Causes Investigations
Non ketotic
hyperglycinaemia
Plasma and CSF amino acids
Disorders or creatine
metabolism
Cranial MRS or urine creatine &
guanidinoacetate
GLUT1 deficiency Blood and CSF glucose
Biotinidase deficiency Plasma biotinidase
Peroxisomal disorders Plasma VLCFA, red cell plasmalogens
Molybdenum cofactor
deficiency
Plasma urate and sulphur amino acids
Menkes disease Plasma copper
Hypoglycaemia [any cause]
Maple syrup urine disease Plasma or urine amino acids
Disorders of pyridoxine
and pyridoxal phosphate
metabolism
Trial of treatment,
urine a-aminoadipic semialdehyde,
CSF neurotransmitters
Hyperammonaemia Plasma ammonia
L-2-hydroxyglutaric aciduria Urine organic acids
Mitochondrial disorders,
esp. Alpers’ syndrome
Blood and CSF lactate
NCL [Battens]: infantile,
late infantile and (juvenile)
Electron microscopy of
lymphocytes or skin,
white cell PTT1 or TPP1
enzyme assays
Krabbe (TayeSachs) &
(Sandhoff ) disease
Leukocyte lysosomal enzyme screen
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Acute ataxia: occasionally patients will present with an episodic
ataxia. These patients should be screened for maple syrup urine
disease, hyperammonaemia, GLUT1 deficiency and organic
acidaemias.
(Congenital disorders of
glycosylation)
Transferrin isoelectric focussing
Hypoglycaemia
And others
Notes:
1. Seizures are a late feature of many metabolic disorders.
2. Rare causes are shown in brackets.
3. This list is long and it is advisable to discuss investigations with specialist
first. Investigation of CSF is often useful in patients presenting with fits.
If this is done, ensure that samples are collected correctly for all likely possi-
bilities to avoid need for a repeat lumbar puncture.
Any comatose patient or one who has had a fit for which there is
no explanation even if ‘febrile’, should have their blood glucose
measured. The metabolic causes and investigations of hypo-
glycaemia are listed in Table 4. The investigations should be
taken during hypoglycaemia. As a minimum, some plasma
taken during hypoglycaemia should be kept and stored deep
frozen.
Table 2
HyperammonaemiaMetabolic disorders that may present with a stroke-likeillness
Causes Investigations
Homocystinuria Plasma amino acids and
total homocysteine
Organic acidaemias Urine organic acids
Ornithine transcarbamylase
deficiency
Plasma ammonia
Mitochondrial disorders
(e.g. MELAS)
Blood mitochondrial
DNA mutations
Plasma ammonia should be measured in every undiagnosed
encephalopathic patient since early intervention is essential.
However the interpretation of results can be problematic. Reference
values are less than 50 mmol/l but any difficulty with the ven-
epuncture, including a child struggling or a haemolyzed sample,
may increase the plasma ammonia concentration. Encephalopathic
patients usually have values>100 mmol/l although in the newborn
in the threshold usually taken to be 200 mmol/l. However it must be
emphasized that the interpretation of plasma ammonia concentra-
tions requires careful assessment of the conditions under which the
blood was collected as well as the effect of any treatment of such as
intravenous glucose.
The metabolic causes of hyperammonaemia and investiga-
tions are listed in Table 5.
Congenital disorders of
glycosylation
Serum transferrin
isoelectric focussing
Disorders of acidebase regulationFabry disease Enzyme tests
Table 3
Metabolic acidosis: metabolic acidosis is a common complication
of almost any illness and is usually secondary to tissue hypoxia.
However, if the history suggests previous episodes, there is marked
PAEDIATRICS AND CHILD HEALTH 21:2 52 � 2010 Elsevier Ltd. All rights reserved.
Causes of hypoglycaemia and investigations(taken during hypoglycaemia)
Causes Metabolic investigations
Glycogen storage disease Plasma urea & electrolytes
Disorders of gluconeogenesis Plasma insulin & cortisol
Disorders of fatty acid oxidation Blood glucose, lactate &
3-hydroxybutyrate
Respiratory chain disorders
involving the liver
Plasma free fatty acids
Organic acidaemias Blood spot acyl carnitines
Tyrosinaemia type 1 Liver-function tests &
clotting studies
Ketotic hypoglycaemia Urine organic acids
Endocrine disorders e
hyperinsulinaemia,
adrenal disease,
hypopituitarism, etc.
Liver disease e acute
liver failure, cirrhosis
Others e any severe illness,
poisoning malaria, etc.
Table 4
The major causes of and investigations for metabolicacidosis
Causes Investigations
Organic acidaemias particularly
methylmalonic and
propionic acidaemia
Congenital lactic acidoses
Fructose 1,6-bisphosphatase
deficiency
Defects of ketolysis
Pyroglutamic aciduria
Other causes e including
diabetes and adrenal insufficiency
Blood gases, anion gap
Blood glucose
Blood lactate
Blood 3-hydroxybutyrate
Plasma amino acids
Blood spot acyl carnitines
Urine ketones
Urine organic acids
Table 6
SYMPOSIUM: INBORN ERRORS OF METABOLISM
ketosis or the acidosis persists after tissue perfusion is corrected, the
patient should be investigated for a metabolic problem. The major
causes and the investigations are listed in Table 6.
Respiratory alkalosis: respiratory alkalosis is less common but an
unexplained respiratory alkalosis should be investigated for
hyperammonaemia (see above). This is often a subtle but partic-
ularly characteristic finding in neonates.
Acute liver disease
There are many causes of acute liver disease and the most
common metabolic ones are listed with investigations in Table 7.
Metabolic causes of hyperammonaemia
Causes Investigations
Urea cycle disorders
Organic acidaemias
Disorders of fatty acid
oxidation
Transport defects e
lysinuric protein intolerance,
HHH syndrome,
Citrin deficiency
Others: ornithine
aminotransferase deficiency,
pyruvate carboxylase
deficiency, etc.a
Plasma ammonia
Plasma amino acids
Urine organic acids and
amino acids
Blood spot acyl carnitines
Blood lactate
a For a full list of inborn errors that cause hyperammonaemia see Table
20.2 in Fernandes et al. (2006).
Table 5
PAEDIATRICS AND CHILD HEALTH 21:2 53
Most of these have parenchymal disease with synthetic dysfunc-
tion including hypoalbuminaemia and clotting abnormalities but
some will present with a more obstructive pictures with conju-
gated hyperbilirubinaemia and secondary abnormalities caused
by the failure of absorption of fat soluble vitamins.
Cardiomyopathy and arrhythmias
Patients with inborn errors may present with a severe cardio-
myopathy and life-threatening arrhythmias. Pompe disease and
disorders of fatty acid oxidation mainly present with hyper-
trophy. In mitochondrial and Hurler disease, the findings are
very variable. Many patients with inborn errors are treated with
restricted diets and vitamin supplements are an essential
component. Omitting these supplements even for surprisingly
short periods may result in thiamine deficiency with a marked
cardiomyopathy. Supplements of thiamine may be lifesaving.
The most important causes and the appropriate investigations
are listed in Table 8.
Metabolic causes of acute liver disease
Causes Investigations
Tyrosinaemia type 1
Fructosaemia
Galactosaemia (newborn period)
Respiratory chain
disorders including
Mitochondrial DNA depletion
syndrome
Disorders of fatty acid oxidation
Wilson’s disease
Urea cycle disorders (severe)
Disorders of bile acid synthesis
a-1-Antitrypsin deficiency
Niemann Pick type C and
many others
Liver-function tests,
clotting studies
Blood glucose, lactate &
3-hydroxybutyrate,
Blood spot acyl carnitines
Plasma amino acids
Serum a-fetoprotein
Serum a-1-antitrypsin
Plasma copper and
caeruloplasmin
Urine organic acids including
succinylacetone
Plasma and urine bile acids
Further investigations
including liver scans and
biopsy may be necessary
Table 7
� 2010 Elsevier Ltd. All rights reserved.
Metabolic causes of cardiomyopathy
Causes Investigations
Disorders of fatty acid
oxidation
Organic acidaemias
Respiratory chain disorders
including Barth syndrome
Storage disorders including
lysosomal storage disorders
such as Pompe disease,
Hurler disease
Glycogen storage disease
(type IIIb) and type IV
(Fabry diseasea)
Blood spot acyl carnitines
Urine organic acids
Blood lactate & mtDNA mutations
Blood spot monolysocardiolipin
Urine GAGs [MPS screen]
Blood film for vacuolated
leucocytes
Enzyme studies
GAGs¼ glycosaminoglycans, MPS¼mucopolysaccharidosesa Rare in childhood.b Rarely a presenting feature.
Table 8
Early management of a suspected inborn of metabolism
1. Stop toxic nutrient (protein, galactose, fructose, etc.)
2. General care as with any patient in intensive care
- Secure airway
- Ensure good tissue perfusion
- Treat hypoglycaemia, infection, fits, acidosis,
hyperammonaemia
3. Give high energy intake oral or intravenous. Note: usually
glucose is used but fat emulsions may be given to increase
energy intake except in disorders of fatty acid oxidation
4. Dialysis haemofiltration/haemodialysis (peritoneal dialysis is
used if more efficient methods are not available)
5. Insulin infusion. Note: this is used to reduce catabolism starting
with 0.05 u/kg/h
6. Vitamins and specific therapy e see below
Table 9
SYMPOSIUM: INBORN ERRORS OF METABOLISM
Sudden collapse
Disorders that may respond to pharmacological dosesof vitamins or cofactors
Patients with inborn errors may collapse suddenly. Patients with
neurological problems including coma, those with hypoglycaemia
and liver disease may all have a seizure. They may also develop
cerebral oedema with consequent herniation. Patients with clot-
ting abnormalities may have a cerebral haemorrhage.
Patients with the metabolic acidosis may be able to compensate
with increased respiratory effort for a time but when they can no
longermaintain this, theymay collapse. It is important to anticipate
this and, if necessary, start assisted ventilation at an early stage.
Patients with cardiac disease may develop arrhythmias.
Management
The management of these patients is divided into two sections;
firstly the management of acute illness and secondly the preven-
tion of such illness in the first place. All patients who are at risk of
decompensation should have a plan that starts at home to try to
prevent episodes of decompensation.
Disorder Vitamin
Acute illnessMethylmalonic acidaemia Hydroxocobalamin
Biotinidase deficiency Biotin
Holocarboxylase synthetase
deficiency
Biotin
Homocystinuria Pyridoxine
Pyridoxine dependency,
PNPO deficiency
Pyridoxine, pyridoxal phosphate
Vitamin deficiency, MSUD,
Pyruvate dehydrogenase
deficiency and others
(all rare)
Thiamine
Carnitine Carnitine transporter deficiency
Riboflavin
and occasionally others
Multiple acyl-CoA dehydrogenase def
Table 10
After resuscitation and stabilization it is important to document
the clinical state. For patients with neurological illness, the Glas-
gow coma score should be noted. Efforts should be made to
identify the factor that has precipitated the illness such as infection
or fasting. This is not always possible as sometimes patients
become ill for reasons that are not clear.
The steps that should be taken in the treatment of acute illness
are listed in Table 9, together with notes about each stage of the
process.
Some inborn errors will improve markedly if given pharma-
cological doses of cofactor of the defective enzyme. The most
important disorders that may respond are listed in Table 10.
Special problems: hypoglycaemia: it is important to document
hypoglycaemia correctly. Bedside strip tests only give approxi-
mate value despite the apparent accuracy of the metres so that
PAEDIATRICS AND CHILD HEALTH 21:2 54
blood glucose should always be measured in the laboratory. It
should then be corrected, either orally or intravenously, depend-
ing on the patient’s condition. If corrected with intravenous
glucose, give 2 ml glucose 10%/kg followed by the infusion of
10% glucose approximately equal to the normal glucose utiliza-
tion rate (children 4e7 mg/kg/min; adults 2 mg/kg/min). Blood
glucose concentrations should be reviewed after approximately
15e30 min.
Metabolic acidosis: the blood pH must be monitored carefully.
Peripheral perfusion, dehydration and infection shouldbe corrected
first and appropriate steps taken if the blood pH is critical despite
assisted ventilation. A convenient cut off is pH of <7.1 (or greater
than this if the patient is clearly deteriorating). This situation is not
the same as diabetic ketoacidosis, as the acidosiswill not respond to
insulin quickly. Hence sodiumbicarbonate should be given as a half
correction ((base deficit � weight (kg) � 0.3)/2). The sodium
� 2010 Elsevier Ltd. All rights reserved.
Key learning points
C A high index of suspicion is needed to identify patients with
inborn errors.
C Early diagnosis and treatment are important to achieve a good
outcome.
SYMPOSIUM: INBORN ERRORS OF METABOLISM
bicarbonate should be administered slowly and reviewed
frequently. The plasma electrolytes must also be monitored. Hae-
modialysis should be considered if the plasma sodium starts to rise
or if the acidosis is not controlled.
Hyperammonaemia: the treatment of hyperammonaemic
encephalopathy is urgent. The same steps are followed as those for
the general patient. In addition arginine, sodium benzoate and
sodium phenylbutyrate should be given early if these are available
and the patient transferred to a specialist centre as quickly as
possible.
Cerebral oedema: it cannot be stressed too strongly that early
intervention is essential to prevent cerebral oedema as, once
established, it is difficult to reverse. It is commonly the cause of
death in these patients. The management once oedema is estab-
lished is standard.
Catabolism: acute decompensation in patients with inborn errors
is often precipitated by infection or fasting and triggering catabo-
lism. Every effort should be made to reverse this. A high energy
intake is given either orally or intravenously. More calories can be
given more quickly orally which is the preferred route if at all
possible. However if the patient cannot tolerate oral feeding,
glucose should be given intravenously, if necessary by central line.
Protein should always be introduced fairly early since failure to do
so will prolong the catabolic state.
Specific treatment: in a few disorders specific management is
vital. In the urea cycle disorders, the use of sodium benzoate,
sodium phenylbutyrate and arginine is essential. In tyrosinaemia
type 1, nitisinone (NTBC) is needed urgently to prevent severe
liver damage. In maple syrup urine disease, encephalopathy
results from the accumulation of branched-chain amino acids
(BCAA). This can be reduced by giving a BCAA-free amino acid
mixture. It is usually given enterally but intravenous preparations
are now available at a few specialist centres. Fructose, sorbitol and
sucrose must be omitted from patients with fructosaemia and
fructose 1,6-bisphosphatase deficiency during acute illness.
Full details of the emergency management of inborn errors that
may present acutely are on the British Inherited Metabolic Disease
Group (BIMDG) website. These are readily accessible and free.
Haemofiltration: the prognosis is poor for patients with severe
hyperammonaemia, especially for babies with values >1000
mmol/l, and this needs to be discussed with the parents before
proceeding with invasive management. If these patients are to be
managed actively, haemofiltration should be started as soon as
possible. Haemofiltration is also needed for severe acidosis
(particularly organic acidaemias) or encephalopathy (particularly
maple syrup urine disease). This intervention can be lifesaving
and will reduce subsequent handicap.
Prevention of acute decompensation
Many inborn errors are stable for much of the time but still have
episodes of acute illness. Prevention is an important part of the
management for these patients. The families must understand
the disorder, be taught to recognise both precipitating factors and
PAEDIATRICS AND CHILD HEALTH 21:2 55
early symptoms. The factors that commonly precipitate decom-
pensation include fasting and infection. The earliest symptoms
are usually just not feeling well, anorexia, vomiting, ataxia or, in
some conditions, hyperventilation. Each patient is different and it
is important to identify the earliest symptoms and discuss these
with the family.
The family should have clear instructions of exactly what to do
and when to make decisions. Almost invariably the mainstay of the
treatment at home is a high carbohydrate drink given frequently
including during the night. The family should always carry details
of their condition and the acute management. A laminated A5 sheet
has been found tobe very acceptable.More details of the emergency
regimens can be found in Dixon and Leonard (1992).
Anaesthesia and surgery may also cause problems. If the patient
is due to have an elective procedure with an anaesthetic then this
requires careful planning (for more information please refer to the
protocols on theBIMDGwebsite). It is essential to ensure that a high
calorie intake is given throughout and after the procedure to avoid
the triggering decompensation.
Conclusions
Inborn errors that present acutely are often treatable and delay
will worsen the outcome. It is important to have a simple strategy
for identifying patients at high risk. Treatment does not need to
wait for a diagnosis but can start at once. Every effort should be
made to prevent or reduce episodes of decompensation. A
FURTHER READING
Clarke JTR. A clinical guide to inherited metabolic diseases. 3rd Edn.
Cambridge: Cambridge University Press, 2006.
Detailedand free instructions on the acute andprospectivemanagement of
inborn errors of metabolism and can be found on the British Inherited
Metabolic Disease Group (BIMDG) http://www.bimdg.org.uk/.
For more information about individual disorders readers should consult:
Fernandes J, Saudubray JM, van den Berghe G, et al. Inborn metabolic
diseases: diagnosis and treatment. 4th Edn. Heidelberg: Springer,
2006.
For details about the diagnosis and management of inborn errors in the
perinatal period refer to: Leonard JV, Morris AA. Diagnosis and early
management of inborn errors of metabolism presenting around the
time of birth. Acta Paediatr 2006; 95: 6e14.
For background to emergency regimens: Dixon MA, Leonard JV. Intercur-
rent illness in inborn errors of intermediary metabolism. Arch Dis Child
1992; 62: 1387e91.
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