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

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

• 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 variants
• Onset of infantile seizures
• Congenital form
• Forme fruste
• Late childhood regression
• Preserved speech variant

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Exclusion mapping

• Genetics of the disease
• Not a genetic disease
• Mitochondrial inheritance
• Autosomal inheritance with sex limited expression
• X-linked dominant inheritance
• with lethality in males

X chrom.
Maternal
Paternal
Minimal Critical Region
X
Haplotype Analysis
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Search 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 (Methyl CpG binding protein 2)

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MeCP2 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 gt10 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 silencing.

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Interaction of MeCP2 protein with HDAC
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MECP2 mutations identified
Recurrent MECP2 mutations
316C?T R106W
502 C?T R168X
763 C?T R255X
808 C?T R270X
Exons II III

IV
1 26 235
376 486
625
930 1461
916C?T R306C
397C?T R133C
473C?T T158M
880 C ?T R294X
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Important!
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.
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A highly likely scenario on the consequences of
MECP2 mutations.
trc
MeCP2
Methylated promoter
Transcriptional silencing
Transcriptional noise
Methylated promoter
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Important 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

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Male Cases
A
41 (36-47)
36 (28-43)
56 (50-64)
T allele
44 (36-50)
59 (53-64)
64 (57-72)
C allele