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Two examples of human genetic disease the muscular

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Unformatted text preview: terile mutations (developmental or gametogenesis) • Lethal mutations (essential gene functions) homeotic mutation Humans • Walk into your office with a Blue Cross card • Pedigree analysis - does a disease run in families? Two Examples of Human Genetic Disease • The muscular dystrophies: • Progressive muscle weakness and degeneration • Two forms (Duchenne MD and Becker MD) resulting from mutations in the same gene on the X chromosome • Triplet repeat disorders The Dystrophies • DMD – Fatal (mid-20’s) • BMD – Typically nonfatal – Severe muscle wastage – Progressive mild muscle degeneration – Wheelchair-bound by age 12 – Still mobile through 40’s – Heart and lungs involved – No heart and lung involvement – Dystrophin absent null mutation Text – Dystrophin present hypomorphic mutation Dystrophin • The largest human gene • 97 exons, 96 introns • Anchors actin to the extracellular matrix • Hypothesize about the difference between DMD and BMD... muscle needs to be attached for maintenance, if not attached to extracellular matrix, you die null can be caused by deletion, frameshift, partial loss mutation: regulatory mutation, small insertion, missense mutations Why the difference? • DMD mutations are frameshifts • BMD mutations are point mutations, or otherwise leave reading frame intact Triplet Repeat Diseases • Examples: Fragile X Syndrome, Huntington Disease, many other neurodegenerative disorders • Caused by expansion of a normally-occuring trinucleotide repeat Huntington Disease • Progressive ataxia and neurodegeneration, starting in the mid-40’s; fatal • Normal gene: 6-35 CAG (glu) repeats • Disease allele: 35-120 repeats Huntington Disease • Number of repeats is correlated to disease age of onset and severity • Severity increases (and age of onset decreases) with each generation (anticipation) • Number of repeats increases with each generation Triplet Repeat Diseases • Most triplet repeat diseases display anticipation no consistency in where repeat is located ...
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