myotonic dystrophy (dm) 1 is an autosomal dominant neuromuscular disorder affecting approximately 1 in 8000 individuals. affected individuals display a wide range of symptoms including myotonia, skeletal muscle weakness and wasting, cardiac conduction abnormalities, and cataracts. despite cloning of the locus, the complex disease phenotype of dm has proven difficult to interpret, and the exact role of dmpk in the pathogenesis of dm remains unclear.