Intro to MEDI 545
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Nonmendelian Kalıtım: Dinamik mutasyonlar Objectifler Üçlü nukleotid tekrarları Fragil X sendromu, Friedreich’s ataxia, Huntington’s hastalığı ve Myotonic distrofi Tarihçe 1991’de gözlendiler Üçlü nukleotidlerde stabil olmayan artışlar izlendi Tekrarlar normalde populasyonda polimorfik, fakat ailelerde stabil Tekrarlar etkilenen ailelerde stabil değil Artış çok farklı değerlerde olabilir 14 stabil olmayan Trinukleotid tekrarı ve bunlarla ilgili hastalıklar AUG TAA CGG GAA Fredreich’s Ataxia Fragil X Sendromu Fragil XE MR CAG CTG Myotonik Distrofi Spinobulbar Muscular Atrophy Huntington’s Disease Dentatorubral-Pallidoluyslan Atrophy Spinocerebellar Ataxia Type 1 Spinocerebellar Ataxia Type 1 Spinocerebellar Ataxia Type 2 Spinocerebellar Ataxia Type 6 Spinocerebellar Ataxia Type 7 Spinocerebellar Ataxia Type 8 Spinocerebellar Ataxia Type 12 Machado-Joseph Disease (SCA3) AUG TAA CGG GAA Fredreich’s Ataxia Fragile X Syndrome Fragile XE MR CAG CTG Myotonic Dystrophy Spinobulbar Muscular Atrophy Huntington’s Disease Dentatorubral-Pallidoluyslan Atropphy Spinocerebellar Ataxia Type 1 Spinocerebellar Ataxia Type 1 Spinocerebellar Ataxia Type 2 Spinocerebellar Ataxia Type 6 Spinocerebellar Ataxia Type 7 Spinocerebellar Ataxia Type 8 Spinocerebellar Ataxia Type 12 Machado-Joseph Disease (SCA3) AUG CGG TAA CAG GAA Intronik 5’ UTR CTG 3’ UTR Polyglutamine Kodlama yapan bölgede Ortak özellikler: Nörolojik hastalık Genelde Otozomal Dominant –X-bağlı veya resesif olabilirler Azalmış penetrans gösterebilirler Slipped Mispairing underlies triplet repeat expansion 5’ Lagging Strand Template (A) Leading Strand Template 3’ 5’ Polymerization proceeds from 5’ to 3’ for the newly synthesized DNA strands. On the lagging strand, synthesis proceeds 5’ to 3’ for each Okazaki fragment, but overall lagging strand synthesis proceeds 3’ to 5’ as the fragments extend, meet and are ligated together, indicated by 1,2,3. 3 2 5’ Okazaki Fragments 3’ 5’ (B) Slipped Mispairing underlies triplet repeat expansion 5’ Lagging Strand Template Leading Strand Template (A) 3’ 5’ Polymerization proceeds from 5’ to 3’ for the newly synthesized DNA strands. On the lagging strand, synthesis proceeds 5’ to 3’ for each Okazaki fragment, but overall lagging strand synthesis proceeds 3’ to 5’ as the fragments extend, meet and are ligated together, indicated by 1,2,3. 3 2 5’ Okazaki Fragments 3’ 5’ (B) Fragil X X-bağlı dominant penetrans azlığı gösterir Orta düzeyde mental retardasyon – 1/4000 erkeklerde; 1/8000 dişilerde X kromozomunda (Xq27.3) “fragil” bölge dekondanse Fragil X Mental Retardasyon gen 1 FMR1 (CGG)n 614 amin o ac ids (69 kD) AUG 1 2 3 4 5 6 7 8 38 kb 9 10 TAA 11 12 13 14 15 16 17 Klinik özellikler: Fragil X Uzun yüz – Büyük kulaklar Mental gerilik (I.Q. 20-60) Dikkat kusuru/hiperaktivite Fragile X in males 2 yrs. 5 yrs. 22 yrs. Fragile X in females Fragil X’de CGG 5’ UTR de FMR1 geninde Allel tipleri: Normal allel – 7-40 CGG Premutasyon allel - 60-200 Hasta allel - >200 den binlerce tekrara kadar İşlev kaybı Fragil X CpG Island 5’ Transcription Translation (CGG) n 3’ 40 repeats Common 41-60 repeats Intermediate 61-200 repeats > 200 repeats, methylated Premutation Male Female 1/25 1/16 1/1000 1/350 Full mutation 1/4000 1/8000 FMR1 Repeat Instability mean 94,25 86,25 85,25 90 111 500 II 88 104 III >230 95 118 93 31 Full mutation Premutation Normal 32P-CGG I probe of PCR Functional domains in the FMR protein NLS 111-152 111-152 KH1 206-280 206-280 KH2 NES 281-422 425-441 281-422 425-441 RGG 527-552 527-552 Cytoplasmic protein NLS-nuclear localization sequence (Eberhardt, et al. 1996. Hum.Mol.Gen) KH-homology to hnRNP K (Siomi, et al. 1993. Cell) NES-nuclear export sequence (Eberhardt, et al. 1996. Hum.Mol.Gen) RGG-arginine-glycine-rich region (Siomi, et al. 1993. Cell) Model for FMRP function in neurons AXON FMRP DENTRITE mGluR Glu Spine maturation; synaptic plasticity Friedreich Ataxia 1/50,000 otosomal recessive spinocerebellar ataxia www.barnstormers.org.uk/ images/jamie1.jpg Friedreich Ataxia AAG tekrarları intron frataxin de Alel Tipleri: Normal allel - <34 tekrar Taşıyıcı allel – 36-100 tekrar Hasta allel - >100 tekrar AUG CGG TAA GAA CAG CTG Frataxin mitokondrial protein Demir metabolismasında iş görür. Huntington Disease (HD) Otosomal Dominant (~1/25,000,) Orta yaşta başlar ölümle sonuçlanır. Atrophy of the caudate and putamen HD CAG tekrarı ile oluşur. polyglutamin-kodlayan gende CAG ekson 1de Normalde – 9-35 CAG tekrar Hastalarda – 36+ tekrar üstü 120 ye kadar. Solid line – avg age at onset; shaded area shows rage of age of onset Artış mayozda oluşur Huntington Hastalığı ve Founder (Kurucu) etkisi Myotonik Distrofi Myotonic Dystrophy CTG tekrarı CTG tekrarı 3’UTR DMPK geni (19q13) – bir protein kinase Normal allel – 5-30 CTG tekrar Orta – 50-80 tekrar Klasik allel – 80-150 tekrar Kongenital – 2,000+ tekrar Anticipation in Myotonic Dystrophy mild Repeat size in DMPK gene 60, 6 5, 7 classic classic 90, 5 96, 7 4, 12 congenital congenital 2150, 12 2900, 4 Sonuç Üçlü nükleotid tekrarları hastalıklar oluşturabilir. Myotonic Dystrophy Huntington’s Disease Fragile X Syndrome Friedreich’s Ataxia