thalassemia modul 3

MKK. SISTEM HEMATOLOGI dan MYELOPROLIFERATIF REZDY TOFAN BHASKARA THALASSEMIA 20 Oktober 2011 105070107121003

PDKBI 2010

1. Describe in brief pathophysiology of thalassemia!

The thalassemia syndromes were among the first genetic diseases to be understood at

the molecular level. More than 200 -globin and 30 -globin mutations deletions

have been identified; these mutations result in decreased or absent production of one

globin chain ( or ) and a relative excess of the other. The resulting imbalance leads

to unpaired globin chains, which precipitate and cause premature death (apoptosis) of

the red cell precursors within the marrow, termed ineffective erythropoiesis. Of the

damaged but viable RBCs that are released from the bone marrow, many are removed

by the spleen or hemolyzed directly in the circulation due to the hemoglobin

precipitants (Figure 1). Combined RBC destruction in the bone marrow, spleen, and

eriphery causes anemia and, ultimately, an escalating cycle of pathology resulting in

the clinical syndrome of severe thalassemia.

Damaged erythrocytes enter the spleen and are trapped in this low pH and low oxygen

environment; subsequent splenomegaly exacerbates the trapping of cells and worsens

the anemia. Anemia and poor tissue oxygenation stimulate increased kidney

erythropoietin production that further drives marrow erythropoiesis, resulting in

increased ineffective marrow activity and the classic bony deformities associated with

poorly managed thalassemia major and severe thalassemia intermedia. Anemia in the

severe thalassemia phenotypes necessitates multiple RBC transfusions and, over time,

without proper chelation, results in transfusion-associated iron overload. In addition,

ineffective erythropoiesis enhances gastrointestinal iron absorption and can result in

iron overload, even in untransfused patients who have thalassemia intermedia. It has

long been recognized that the severity of ineffective erythropoiesis affects the degree

of iron loading, but until the recent discovery of hepcidin and understanding, its role

in iron metabolism the link was not understood.

Hepcidin, an antimicrobial hormone, is recognized as playing a major role in iron

deficiency and overload. Hepcidin initially was discovered due to its role in the

etiology of anemia of chronic inflammation or chronic disease. Elevated levels,

associated with increased inflammatory markers, maintain low levels of circulating

bioavailable iron in two important ways: (1) by preventing iron absorption and

transport from the gut and (2) by preventing release and recycling of iron from

macrophages and the reticuloendothelial system. Conversely, inadequate hepcidin

allows increased gastrointestinal absorption of iron and ultimately may lead to excess

iron sufficient to result in organ toxicity.


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Figure 1. Pathophysiology of thalassemia

Iron not bound to transferrin, also referred to as nontransferrin-bound iron, damages the endocrine organs, liver, and heart. Nontransferrinbound iron can result in myocyte damage leading to arrhythmias and congestive heart failure, the primary causes of death in patients who have thalassemia. Appropriate chelation therapy and close monitoring of cardiac siderosis can avoid this devastating complication (see the article by Kwiatkowski elsewhere in this issue for discussion of iron chelators).


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2. Describe in brief clinical and genetic classification of thalassemia!

As knowledge about the thalassemias has grown, different approaches to their classification

have evolved and gradually become more sophisticated. The disease can now be described at

several levels. First, there is a phenotypic classification based on its severity: this

classification says nothing about the genetic constitution of a particular patient, but simply

describes, in very general terms, a constellation of clinical features. Second, the thalassemias

can be defined by the particular globin(s) that is (are) synthesized at a reduced rate. In effect,

this constitutes a genetic classification in that, in most cases, it describes the gene (or genes)

that must be affected by the thalassemia mutation. Finally, it is now often possible to

subclassify many thalassemias according to the particular mutation that is responsible for

defective globin synthesis.

In clinical practice it is very useful to retain each of these classifications. Much of our

approach to treatment is still determined by characterization of the disease at a clinical level.

However, for an accurate assessment of the likely outcome it is becoming increasingly

important to go to at least the next step, that is, a genetic classification by the particular

globins involved. Indeed, in current day-to-day management of thalassemia it is often

extremely helpful to be able to analyse the disorder at the molecular level, particularly if its

prenatal detection is contemplated.


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Clinical Classification

Based on clinical assessment, the thalassemias can be divided into hydrops fetalis which are

four genes deletion -thalassemia, thalassemia major which are severe and transfusion

dependent, and thalassemia minor which can only be identified hematologically and usually

represent the carrier states or traits (Table 1).

Table 1. Clinical Classification of the Thalassemias

Hydrops fetalis

Four genes deletion -thalassemia

Thalassaemia major

Transfusion dependent, homozygous

0-thalassemia or other combonations of -thalassemia trait

Thalassaemia intermedia

Homozygous -thalassemia

Heterozygous -thalassemia

-thalassemia and hereditary persistence of fetal Hb

Hemoglobin H disease

Thalassemia minor

0-thalassemia trait

+-thalassemia trait

Hereditary persistence of fetal Hb

-thalassemia trait

0-thalassemia trait

+-thalassemia trait

Although -thalassemia major usually results either from the homozygous inheritance of a

particular mutation or from the compound heterozygous state for two different mutations, it

has become apparent that there are rare forms of moderately severe -thalassemia that result

from the action of a single mutant gene; that is, they are dominantly inherited.

Another term,‘thalassemia intermedia’, though it has an old-fashioned ring about it, is still

retained and is extremely useful in clinical practice. It describes conditions which, though not

as severe as the major forms, are associated with a more severe degree of anemia than is

found in the trait. In practice, this term encompasses a wide spectrum, ranging from disorders

which are almost as serious as major forms to asymptomatic conditions which are only


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slightly more severe than the trait. Finally, some heterozygotes for thalassemia mutations are

clinically and hematologically normal; they are sometimes designated ‘silent’ carriers.

Genetic Classification

The thalassemias are classified according to their genetic basis by describing the globin

subunit which is synthesized at a reduced rate. A classification of the syndromes at this level

is shown in Table 2. The genetic classification of the thalassemias divides them broadly into

, , , , and varieties, depending on which globin or globins are underproduced.

Newcomers to the field may be confused when they see that, as well as the thalassemias,

Table 2 includes ‘hereditary persistence of fetal hemoglobin’. It seems reasonable to include

this heterogeneous collection of conditions with the thalassemias since many of them are, in

effect, forms of or thalassemia in which globin imbalance is almost entirely

compensated by a genetically determined persistence of relatively high levels of fetal

hemoglobin production. In each of the later chapters that deal with particular forms of

thalassemia in detail, their classification is considered at greater length. But as a general

introduction it may be helpful to outline the main features of the different genetic forms here.

-THALASSEMIA SYNDROMES

These are usually caused by gene deletions(Table 2). As there are normally four copies of the

-globin gene the clinical severity can be classified according to the number of genes that are

missing or inactive. Loss of all four genes completely suppresses -chain synthesis and since

the -chain is essential in fetal as well as in adult hemoglobin this is incompatible with life

and leads to death in utero (hydrops fetalis). Three -gene deletions leads to a moderately

severe (Hb 7-11 g/dl) microcytic, hypochromic anemia with splenomegaly. This is known as


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HbH disease because HbH (4) can be detected in red cells of these patients by

electrophoresis or in reticulocyte preparations. In fetal life, Hb Barts (4) occurs.

The -thalassemia traits are caused by loss of one or two genes and are usually not associated

with anemia, although the MCV and MCH are low and the red cell count is over 5.5 x 1012/L.

Hemoglobin electrophoresis is normal and /-chain synthesis studies or DNA analyses are

needed to be certain of the diagnosis. The normal /-synthesis ratio is 1:1 and this is

reduced in the -thalassemias and raised in -thalassemias. Uncommon non-deletional forms

of -thalassemia are caused by point mutations producing dysfunction of the genes or rarely

by mutations affecting termination of translation which give rise to an elongated but unstable

chain, e.g. Hb Constant Spring.

-THALASSEMIA SYNDROMES

-THALASSEMIA MAJOR

This condition occurs on average in one in four offspring if both parents are carriers of the -

thalassemia trait. Either no -chain (0) or small amounts (+) are synthesized. Excess -

chains precipitate in erythroblasts and in mature red cells causing the severe ineffective

erythropoiesis and hemolysis that are typical of this disease. The greater the -chain excess,

the more severe the anemia. production of -chains helps to ‘mop up’ excess -chains and to

ameliorate the condition. Over 200 different genetic defects have now been detected.

Unlike -thalassemia, the majority of genetic lesions are point mutations rather than gene

deletions. These mutations may be within the gene complex itself or in promoter or enhancer

regions. Certain mutations are particularly frequent in some communities and this may

simplify antenatal diagnosis aimed at detecting the mutations in fetal DNA. Thalassemia

major is often a result of inheritance of two different mutations, each affecting -globin

synthesis (compound heterozygotes). In some cases deletion of the gene, and genes or

even , , and genes occurs. In others, unequal crossing-over has produced fusion genes

(so called Lepore syndrome named after the first family in which this was diagnosed).

-THALASSEMIA MINOR (TRAIT)

This is a common, usually symptomless, abnormality characterized like -thalassemia trait

by a hypochromic, microcytic blood picture (MCV and MCH very low) but high red cell

count (>5.5 x 1012/L) and mild anemia (Hb levels 10-15 g/dl). It is usually more severe that trait; a raised HbA2 (>3.5%) confirms the diagnosis. One of the most important indications

for making the diagnosis is that it allows the possibility of prenatal counseling to patients

with a partner who also has a significant hemoglobin disorder. If both carry -thalassemia

trait there is a 25% risk of a thalassemia major child.


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Table 4. Genetic Basis and Clinical Manifestations of Common -Thalassemia Syndromes

THALASSEMIA INTERMEDIA

Cases of thalassemia of moderate severity (Hb 7.0-10.0 g/dl) who do not need regular

transfusions are called thalassemia intermedia. This is a clinical syndrome which may be

caused by a variety of genetic defects. It may be caused by homozygous -thalassemia with

production of more HbF than usual or with mild defects in -chain synthesis, or by -

thalassemia trait alone but of unusual severity (‘dominant’ -thalassemia) or -thalassemia

trait in association with mild globin abnormalities such as Hb Lepore. The coexistence of -

thalassemia trait improves the hemoglobin level in homozygous -thalassemia by reduction

the degree of chain imbalance and thus of -chain precipitation and ineffective

erythropoiesis. Conversely, patients with -thalassemia trait who also have excess (five or

six) genes tend to be more anemic than usual. The patient with thalassemia intermedia may

show bone deformity, enlarged liver and spleen, extramedullary erythropoiesis and features

of iron overload caused by increased iron absorption. HbH disease, three-gene deletion -

thalassemia is a type of thalassemia intermedia without iron overload or extramedullary

hematopoiesis.


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3. Describe clinical features and laboratory findings to diagnose β-Thalassemia major!

1. Severe anemia becomes apparent at 3-6 months after birth when the switch from - to -

chain production should take place.

2. Enlargement of the liver and spleen occurs as a result of excessive red cell destruction,

extramedullary hematopoiesis and later because of iron overload. The large spleen

(splenomegaly) increases blood requirements by increasing red cell destruction and

pooling, and by causing expansion of the plasma volume.

3. Expansion of bones caused by intense marrow hyperplasia leads to a thalassemic facies

(Figure 3), and to thinning of the cortex of many bones with a tendency to fractures and

bossing of the the skull with a ‘hair-on-end’ appearance on X-ray (Figure 4).

4. The patient can be sustained by blood transfusions but iron overload caused by repeated

transfusions is inevitable unless chelation therapy is given. Each 500 ml of transfused

blood contains about 250 mg iron. To make matters worse,iron absorption from food is

increased in -thalassemia, probably secondary to ineffective erythropoiesis. Iton

damages the liver, the endocrine organs (with failure of growth, delayed or absent

puberty, diabetes mellitus, hypothyroidism, hypoparathyroidism) and the myocardium. In

the absence of intensive iron chelation death occurs in the second or third decade, usually

from congestive heart failure or cardiac arrhytmias. Skin pigmentation as result of excess

melanin and hemosiderin gives a slatey grey appearance at an early stage of iron

overload.

Figure 3. Thalassemic facies Figure 4. Hair-on-end appearance

5. Infections may occur for a variety of reasons. In infancy, without adequate transfusion,

the anemic child is prone to bacterial infections. Pneumococcal, Hemophilus and

meningococcal infections are likely if splenectomy has been carried out and prophylactic

penicillin is not taken. Yersinia enterocolitica occurs particularly in iron-loaded patients

being treated with desferrioxamine; it may cause severe gastroenteritis. Transmition of

viruses by blood transfusion may occur. Liver disease in thalassemia is most frequently a


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result of hepatitis C but hepatitis B is also common where the virus is endemic. Human

immunodeficiency virus (HIV) has been transmitted to some patients by blood

transfusion.

6. Osteoporosis may occur in well-transfused patients. It is more common in diabetic

patients.

Laboratory Findings

There is a severe hypochromic, microcytic anemia with raised reticulocyte percentage

with normoblasts, target cells and basophilic stippling in the blood film (Figure 5).

Hemoglobin electrophoresis reveals absence or almost complete absence of HbA with

almost all the circulating hemoglobin being HbF. The HbA2 percentage is normal,

low or slightly raised. /-globin chain synthesis studies on reticulocytes show an

increased : ratio with reduced or absent -chain synthesis. DNA analysis can be

used to identify the defect on each allele.

Figure 5. Thalassemia: the blood film shows marked hypochromic

microcytic cells with target cells & poikilocytosis


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4. Describe in brief assessment of iron overload!

Assessment of Iron Status

The tests that may be performed to assess iron overload are listed in Table 3. Tests may also

be carried out to determine the degree of organ damage caused by iron. The serum ferritin is

the most widely used test. It is usual in thalassemia major to attempt to keep the level

between 1000 and 1500 g/L, when the body iron stores are about 5 to 10 times normal.

However, the serum ferritin is raised in relation to iron status in viral hepatitis and other

inflammatory disorders, and should therefore be interpreted in conjunction with other tests

such as liver biopsy, urine excretion of iron in response to deferrioxamine, skin pigmentation

and function of the heart, liver & endocrine & the clinical picture.


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Table 3. Assessment of Iron Overload

Assessment of iron stores

Serum ferritin

Serum iron & percentage saturation of transferrin (TIBC)

Bone marrow biopsy (Perls’ stain) for reticuloendothelial stores

DNA test for mutation resulting in Cys282 Tyr in the HFE gene

Liver biopsy (parenchymal & reticuloendothelial stores)

Liver CT scan or MRI

Cardiac MRI

Desferrioxamine iron excretion test (chelatable iron)

Repeated phlebotomy until iron deficiency occurs

Assessment of tissue damage caused by iron overload

Cardiac : clinical, chest x-ray, ECG, 24-h monitor, echocardiography, radionuclide (MUGA) scan to

check LV ejection fraction at rest & with stress

Liver : liver function tests, liver biopsy, CT scan

Endocrine

: clinical examination (growth & sexual development), glucose tolerance test, pituitary

gonadotrophin release tests, thyroid, parathyroid, gonadal & adrenal function, growth

hormone assays, radiology for bone age, isotopic bone density study


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5. Describe in brief the management of thalassemia!

Regular blood transfusions are needed to maintain the Hb over 10 g/dl at all times

(Figure 6). This usually requires 2-3 units every 4-6 weeks. Fresh blood, filtered to

remove white cells, gives the best red cell survival with fewest reactions. The patients

should be genotyped at the start of the transfusion programme in case red cell

antibodies against transfused red cells develop.

Figure 6. Management of Thalassemia and Treatment-Related Complications

Iron chelation therapy is used to treat iron overload. Unfortunately desferrioxamine is

inactive orally. It may be given by a separate infusion bag 1-2 g with each unit of

blood transfused and by subcutaneous infusion 20-40 mg/kg over 8-12 hours, 5-7

days weekly. It is commenced in infants after 10-15 units of blood have been

transfused. Iron-chelated by desferrioxamine is mainly excreted in the urine but up to

one-third is also excreted in the stools. If patients comply with this intensive iron

chelation regime, life expectancy for patients with thalassemia major and other

chronic refractory anemias receiving regular blood transfusion improves considerably.

Desferrioxamine is not without side-effects, especially in children with relatively low


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serum ferritin levels, including high tone deafness, retinal damage, bone abnormalities

and growth retardation. Patients should have auditory and funduscopic examinations

at regular intervals. Deferiprone (L1) is used alone or in combination with

desferrioxamine. The two drugs have an additive or even synergistic action on iron

excretion. Alone it is less effective than desferrioxamine. Compliance is usually

better. Side-effects include an arthropathy, agranulocytosis or severe neutropenia,

gastrointestinal disturbance and zinc deficiency.

Regular folic acid (e.g. 5 mg daily) is given if the diet is poor.

Vitamin C 200 mg daily increases excretion of iron produced by desferrioxamine.

Splenectomy may be needed to reduce blood requirements. This should be delayed

until the patient is over 6 years old because of the high risk of dangerous infections

post-splenectomy.

Endocrine therapy is given either as replacement because of end-organ failure or to

stimulate the pituitary if puberty is delayed. Diabetic will require insulin therapy.

Patients with osteoporosis may need additional therapy with increased calcium and

vitamin D in their diet, together with administration of a bisphosphonate.

Immunization against hepatitis B should be carried out in all non-immune patients.

Treatment for transfusion-transmitted hepatitis C with -interferon and ribavirin is

needed if viral genomes are detected in plasma.

Allogeneic bone marrow transplantation offers the prospect of permanent cure. The

success rate (long-term thalassemia major-free survival) is over 80% in well-chelated

younger patients without liver fibrosis or hepatomegaly. A human leucocyte antigen

(HLA) matching sibling (or rarely other family member or matching unrelated donor)

acts as donor. Failure is mainly a result of recurrence of thalassemia, death (e.g. from

infection) or severe chronic graft-versus-host disease.


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6. Describe in brief the complications of thalassemia!

Possible complication of thalassemia include:

Iron overload: people with thalassemia can get too much iron in their bodies, either from the disease itself or from frequent blood transfusions. Too much iron can result in damage to your heart, liver and endocrine system, which includes glands that produce hormones that regulate processes throughout your body.

Infection. People with thalassemia have an increased risk of infection. This is especially true if you’ve had spleen removed.

In cases of severe thalassemia, the following complications can occur:

Bone deformities: Thalassemia can make your bone marrow expand, which causes your bones to widen. This can result in abnormal bone structure, especialy in your face and skull. Bone marrow expansion also makes bones thin and brittle, increasing the chance of broken bones.

Enlarged spleen (Splenomegaly). The spleen helps your body fight infection and filter unwanted material, such as old or damaged blood cells. Thalassemia is often accompanied by the destruction of a large number of red blood cells, making your spleen work harder than normal, causing it to enlarge. Splenomegaly can make anemia worse, and it can reduce the life of tansfused red blood cells. If your spleen grows too big, it may need to be removed.

Slowed growth rates. Anemia can cause a chid’s growth to slow. Puberty also may be delayed in children with thalassemia.

thalassemia modul 3

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