Rett Syndrome Presented by: Ashley Owen University of Wisconsin-Eau Claire November 30, 2004 What is RTT? Neurodevelopmental disorder cased by mutations in the methyl-CpG-binding protein 2 (MECP2) and is characterized by the loss of acquired skills after a period of normal development in infant girls. Symptoms after 7 to 18 months Mild learning difficulties Disturbances with breathing and cardiac rate Bowel immobility Screaming fits Autistic features Microcephaly Seizures Hand stereotypes Washing, clapping, mouthing Decrease in head growth Small statue Teeth grinding “eye pointing” Inheritance Prevalence 1/10,000-15,000 females X-linked dominant mutation De novo Inherited from parent with the disease causing mutation and germline mosaicism Mother would have XCI and be unaffected Males 47, XXY Identified as RTT Somatic mosaicism XCI 46, XY Severe neonatal encephalopathy Leads to death “Disease of the brain” Gene of Interest: MECP2 Methyl-CpG-Binding Protein Two domains Methyl-CpG-binding domain (MBD) Transcriptional repression domain (TRD) Location: Xq28 Pericentromeric heterochromatin Transcriptional silencing/repression, epigenetic regulation, nuclear structure (chromatin) 5-methylcytosine rich heterochromatin MBD Nan, X., Meehan, R.R., & Bird, A. Located between amino acid 89 and 162 Symmetrical methylated CpG dinucleotides Binds to minor groove of beta DNA MBD(cont.) Nan, X., Meehan, R.R., & Bird, A. Dimerization is not required for binding Monomer MBD and TRD are important for XCI Methyl dependent repression TRD Interacts with co-repressor Sin3A Recruits histone deactylases Exons Exon 1 Non-coding 5‘ untranslated region (UTR) Exon 2 Coding sequence Exon 3 Coding sequence Exon 4 Non-coding 3‘ UTR Coding sequence Polyadenylation creates different protein lengths Structure of Human MECP2 Wan, M., et.al. Detection Lewis, J.D., et.al. Looking for MECPs expression clone Methylated and unmethylated probe Differ from MECP1 MECP1 is a 120kb Tissue distribution Testis Anion/cation ion exchange column Binding specificities 12 methyl-CpGs vs. a pair Obtaining cDNA Lewis, J.D., et.al. Partial amino acid sequence as a primer 340 bp fragment from original PCR to complete library λZAPll ORF 492 amino acids and all 6 major peptides Translational Experiments Lewis, J.D., et.al. SDS-polyacrylamide Relationship between ORF and MECP2 Showed an 81kd sequence cDNA fused into E.Coli with ß-galactosidase gene Bound to methylated probe Conclusion: ORF codes for MECP2 Localization Lewis, J.D., et.al. Immunofluorescence Ab76 serum Stained in heterochromatin areas Parallel satellite DNA in mice Contains 8 CpGs sights Associated with pericentromeric heterochromatin Comparison of Mouse and Human MECP2 Reichwald, K., et.al. •Identity between the mouse and human gene is 68% (average) Mechanism Expressed during organogenesis during embryonic life and in the hippocampus during adult life Other methylated binding proteins take over in other cells during adulthood Believed to be involved in XCI and genetic imprinting Tissue Specific Two transcripts 1.9kb ~10kb Difference in tissue expression Difference in translatability Half life is similar Mutations 99.5% are sporadic Nonsense, missense/frameshifts, deletions Majority are nonsense Detected using PCR and restriction enzyme analysis Occur in CpG sites Hypermutable Methylated in germline and prone to deamination (C to T) Mutations(Cont.) Wan, M., et.al. See word document Structure of Human MECP2 Wan, M., et.al. Treatment No trxt has shown significant improvements Previous trxts L-carnitine Control of seizures Lacked vitamins Naltrexone* Oral opiate antagonist Respiratory features, EEG patterns Folate-Betaine Fatty acid metabolism Respiratory features Ketogenic diet Ongoing trial Methyl-donor group Alter gene expression Recruit other methyl binding groups Current trxt Supportive/symptomatic therapy Occupational/physical therapy Social and Ethical Dilemmas Money…testing in general is expensive Have to show clinical signs/family member Diagnostic testing Test for mutation prenatally Possible involvement with other disorders Mental retardation in males References Hagberg, B.A. and Skjeldal, O.H. (1994). Rett variants: A suggested model for inclusion criteria. Pediatric Neurology, 11, 5-11. Lewis, J.D., et.al. (1992). Purification, sequence, and cellular localization of a novel chromosomal protein that binds to methylated DNA. Cell, 69, 905-914. Nan, X., Meehan, R.R., & Bird, A. (1993). Dissection of the methyl-CpG binding domain from the chromosomal protein MeCP2. Nucleic Acids Research, 21, 4886-4892. Percy, A. K. (2002). Clinical trials and treatment prospects. Mental Retardation and Developmental Disabilities Research Reviews, 8, 106-111. Reichwald, K., et.al. (2000). Comparative sequence analysis of the MECP2-locus in human and mouse reveals new transcribed regions. Mammalian Genome, 11, 182-190. Rett Syndrome, RTT. (2004). Online mendelian inheritance in man, 9 Oct. 2004. Shahbazian, M.D., Antalffy, B., Armstrong, D.L. & Zoghbi, H.Y. (2002). Insight into rett syndrome: MECP2 levels display tissue- and cell-specific difference and correlate with neuronal maturation. Human Molecular Genetics, 11, 115-124. Wan, M. et.al. (1999). Rett syndrome and beyond: Recurrent spontaneous and familial MECP2 mutations at CpG hotspots. American Journal of Human Genetics, 65, 1520-1529. Zoghbi, H.Y. (2004). Rett Syndrome. GeneReviews, www.genetests.org, 29 Sept. 2004. Questions