Abstract
Myotonic dystrophy is a progressive, multi-systemic condition causing muscle weakness and myotonia. Additional symptoms include cataracts, gastrointestinal abnormalities, male reduced fertility, diabetes, and cardiac conduction defects. Myotonic dystrophy type 1 (DM1) is caused by a CTG expansion in the DMPK gene and type 2 (DM2) by a CCTG repeat expansion in the ZNF9 gene. Whereas age of onset correlates with repeat size in DM1 with anticipation, onset and severity do not correlate well with the repeat expansion size in DM2. The non-dystrophic myotonic disorders produce myotonia without muscle weakness. These conditions are caused by mutations in ion channel genes.
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