DMPK and myotonic dystrophy type 1: Myotonic dystrophy type 1 (DM-1) is an autosomal dominant, progressive, multisystemic genetic disorder that mainly causes myotonia, distal limb and facial/neck muscle weakness, cardiac arrhythmia, and cataracts.[1] The prevalence of DM-1 varies between 2.1 and 14.3 per 100,000 people and is less common in Asia.[1] DM-1 is caused by the expansion of CTG repeats of the DMPK gene in chromosome 19q13.3.