Genetics
Myotonic dystrophy is an autosomal dominant disease with an incidence of 5 per 100000. The gene is located on chromosome 19.
The genetic defect is a trinucleotide expansion within the 3' untranslated region of the mRNA of the myotonin-protein kinase gene, which results in decreased expression of the protein.
Myotonic dystrophy exhibits the phenomenon of genetic anticipation - the disease becomes more severe down the generations of an affected family as a result of repeated expansion of the (CTG/CAG)n trinucleotide repeats, probably during gametogenesis.
The number of repeats in affected individuals is very large, about 200 - 400 copies (1).
Reference:
- Fu, Y.-H. et al., Decreased expression of myotonin-protein kinase messenger RNA and protein in adult form of myotonic dystrophy, Science, 1993, 260, p.235-7
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