IDENTIFICATION OF THE MOLECULAR IDENTIFICATION OF THE MOLECULAR MECHANISMS IN RETT SYNDROME AND MECHANISMS IN RETT SYNDROME AND RELATED DISORDERS (RTT-GENET)RELATED DISORDERS (RTT-GENET)

XX

• A childhood neuro-developmental disorder

• Seen almost exclusively in females

• Found in a variety of racial and ethnic groups worldwide

• Dr. Andreas Rett (first description-1966)

• Dr. Bengt Hagberg (worldwide recognition-1983)

• 1/10,000-15,000 females

• 99.5% sporadic :high rate of new mutations

• 1/3 – 1/4 of progressive developmental disabilities in girls

• ~ 10% of profound disability in females

RTT RTT vvariantsariants

• OOnset nset of iof infantile seizurenfantile seizuress

• Congenital formCongenital form

• Forme frusteForme fruste

• Late childhood regressionLate childhood regression

• Preserved speech variantPreserved speech variant

Rett SyndromeRett Syndrome

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Exclusion mappingExclusion mapping

“Minimal Critical Region”

Haplotype Analysis

PaternalMaternal

X chrom.

Genetics of the disease

–Not a genetic disease

–Mitochondrial inheritance

–Autosomal inheritance with sex

limited expression

–X-linked dominant inheritance

with lethality in males

Search for the geneSearch for the gene

Minimal Critical Region Includes Xq28 a chromosome band rich in disease genes

Candidate gene approach Systematic sequencing of all the genes (over 200) in Xq28 was Dr.

Uta Francke (Stanford) and Dr. Huda Zoghbi (Baylor)

Identification of the RTT gene After 14 years of search the RTT gene was finally identified in 1999

MECP2 MECP2 (Methyl CpG binding protein 2)

MeCP2 proteinMeCP2 protein

• 486 amino acids and 52kD.• An abundant mammalian chromosomal protein that binds

to methylated CpG. • Ubiquitously expressed, more abundant in brain.• Can bind to single methyl-CpG pair (unlike MeCP1 which

requires >10 methyl-CpGs to bind DNA)

• Contains four functional domains:– A methyl-CpG binding domain(MBD) – A transcriptional repression domain (TRD)– Nuclear localization signal (NLS)– C-terminal segment

Potentially involved in global gene silencingPotentially involved in global gene silencing.

Interaction of Interaction of MeCP2 protein MeCP2 protein with HDAC with HDAC

MECP2MECP2 mutations identified mutations identified

Exons II III IV

316CTR106W

502 CTR168X

763 CTR255X

397CT R133C

473CTT158M

880 C TR294X

916CTR306C

1 26 235 376 486 625 930 1461

808 CTR270X

Recurrent Recurrent MECP2MECP2 mutations mutations

Rett Syndrome is the first human disease found to be caused by

defects in a protein involved in regulation of gene expression

through its interaction with methylated DNA.

Important!Important!

Methylated promoter

Methylated promoter

MeCP2

Transcriptional silencing

Transcriptional noise

Mutated MeCP2

??

trc

A highly likely scenario on theA highly likely scenario on theconsequences of consequences of MECP2MECP2 mutations. mutations.

Important issuesImportant issues

• Identification of downstream genes regulated by MECP2

• MECP2 mutations and epigenetics• X-inactivation

• Genomic imprinting

• Animal models• Using conditional knock-out technology, mice that lack

MECP2 either in all tissues or selectively in brain was generated (Bird et al., 2001, Guy et al. 2001).

• Cellular defects associated with MeCP2 deficiency in mouse CNS?

• Behavioral defects in mice?

• Drugs, gene therapy, stem cells with normal MECP2 can be the solution for treatment of RTT

A

%T allele

%C allele

41(36-47)

44(36-50)

36(28-43)

59(53-64)

56(50-64)

64(57-72)

Male CasesMale Cases