Stratifying RTT Patients for Stratifying RTT Patients for Clinical TrialsClinical Trials

A Mutation Based ApproachA Mutation Based Approach

John ChristodoulouJohn Christodoulou

NSW Centre for Rett Syndrome ResearchNSW Centre for Rett Syndrome Research

Western Sydney Genetics Program, Children’s Hospital at WestmeadWestern Sydney Genetics Program, Children’s Hospital at Westmead

Disciplines of Paediatrics & Child Health and Genetic Medicine, Disciplines of Paediatrics & Child Health and Genetic Medicine,

University of SydneyUniversity of Sydney

AUSTRALIAAUSTRALIA

““Generic” TherapiesGeneric” Therapies

• potentially of value regardless of the potentially of value regardless of the underlying molecular aetiologyunderlying molecular aetiology– nutritionnutrition

– seizuresseizures

– scoliosis (development of consensus approach?)scoliosis (development of consensus approach?)

– breathing irregularitiesbreathing irregularities

– physiotherapyphysiotherapy

– occupational therapyoccupational therapy

– environmental enrichmentenvironmental enrichment

– whole body vibration training??whole body vibration training??

– other…other…

Environmental EnrichmentEnvironmental Enrichment

• mouse model studiesmouse model studies–mice housed in enriched environments with objects mice housed in enriched environments with objects

of varying textures, sizes, shapes and coloursof varying textures, sizes, shapes and colours

– to stimulate enhanced sensory cognitive and motor to stimulate enhanced sensory cognitive and motor activityactivity

– delayed onset and progression of disease in…delayed onset and progression of disease in…

» Huntington modelHuntington model

» Down syndrome modelDown syndrome model

» Alzheimer modelAlzheimer model

» Fragile X modelFragile X model

» Schizophrenia modelSchizophrenia model

»……and now a RTT modeland now a RTT model

Nithianantharajah and Hannan, Nat Rev Neurosci 2006: 7; 697-709 Nithianantharajah and Hannan, Nat Rev Neurosci 2006: 7; 697-709

Promotion of neuronal activation,signalling and plasticity

MecpMecp22tm1Tamtm1Tam Mice Mice

improved motor coordination isimproved motor coordination islost in heterozygous mice notlost in heterozygous mice notexposed to an enriched exposed to an enriched environmentenvironment

BDNF protein levels in 30 week BDNF protein levels in 30 week old mice in cerebellum old mice in cerebellum - correction towards normal- correction towards normal

Kondo et al Eur J Neurosci, in pressKondo et al Eur J Neurosci, in press

Whole Body Vibration TrainingWhole Body Vibration Training

• first developed to enhance muscle strength in first developed to enhance muscle strength in athletesathletes

• increases bone mass in children and adultsincreases bone mass in children and adults

• improves lower limb skin blood flowimproves lower limb skin blood flow

• limited paediatric experience, but is of benefit in:limited paediatric experience, but is of benefit in:– osteogenesis imperfectaosteogenesis imperfecta

– cerebral palsycerebral palsy

– spinal dysraphismspinal dysraphism

• worthy of a clinical trial in RTT patientsworthy of a clinical trial in RTT patients

Individuals with Individuals with MECP2MECP2 MutationsMutations

Target the mutation Target the mutation

or or

target the mutation’s consequences…target the mutation’s consequences…

““Treating” the Treating” the MECP2MECP2 Mutation Mutation

• nonsense mutations – 30%nonsense mutations – 30%– PTC124PTC124

» penetrates the blood-brain barrier?penetrates the blood-brain barrier?

» converting a nonsense to a missense mutation?converting a nonsense to a missense mutation?

• other mutationsother mutations– novel strategies yet to be developednovel strategies yet to be developed

• modifiers?modifiers?– same mutation, variable severity same mutation, variable severity

(not just skewed XCI)(not just skewed XCI)

What about activating the What about activating the normal normal MECP2MECP2 allele? allele?

• a problem of dosagea problem of dosage– 2 x activity is “toxic” – human and mouse2 x activity is “toxic” – human and mouse

• exogenous MeCP2exogenous MeCP2– expression at 112% of normal in the forebrain restores expression at 112% of normal in the forebrain restores

function function (Jugloff et al, Hum Molec Genet 2008: 17; 1386-1396)(Jugloff et al, Hum Molec Genet 2008: 17; 1386-1396)

• endogenous MeCP2endogenous MeCP2– key brain regions are mosaic for MeCP2 expression in key brain regions are mosaic for MeCP2 expression in

RTT patients RTT patients (LaSalle et al Hum Molec Genet 2001: 10; 1729-1740)(LaSalle et al Hum Molec Genet 2001: 10; 1729-1740)

– Can high MeCP2 expressing cells exert a positive effect Can high MeCP2 expressing cells exert a positive effect on adjacent low or negatively expressing cells?on adjacent low or negatively expressing cells?

MeCP2 target genes as possible MeCP2 target genes as possible substrates for therapeutic interventionsubstrates for therapeutic intervention

• BdnfBdnf

• xHairy2axHairy2a

• DLX5DLX5

• Sgk1Sgk1

• Fkbp5Fkbp5

• ID1-3ID1-3

• FXYD1FXYD1

• IGFBP3IGFBP3

• CrhCrh

• UBE3AUBE3A

• GABRB3GABRB3

• others…others…

ConclusionsConclusionsMulti-pronged approach to therapiesMulti-pronged approach to therapies

• treatment of specific clinical problemstreatment of specific clinical problems–mutation independent mutation independent

• correction of the specific mutationcorrection of the specific mutation

• modulation of modifiersmodulation of modifiers

• increase expression of normal increase expression of normal MECP2MECP2 allele allele– exogenous or endogenous approachesexogenous or endogenous approaches

• modify the expression of specific MeCP2 modify the expression of specific MeCP2 target genestarget genes

Funding AcknowledgementsFunding AcknowledgementsNHMRCNHMRC

International Rett Syndrome AssociationInternational Rett Syndrome Association

Rett Syndrome Research FoundationRett Syndrome Research Foundation

International Rett Syndrome FoundationInternational Rett Syndrome Foundation

Rotary Club of NarellanRotary Club of Narellan

CWA of NSWCWA of NSW

Rett Syndrome Australian Research Rett Syndrome Australian Research FundFund

Tissue Resource Centre, SydneyTissue Resource Centre, SydneyHarvard Brain BankHarvard Brain Bank