Myotonic Dystrophy Myotonic dystrophy is an dominant disorder characterized by myotonia, muscular dystrophy, cataracts, hypogonadism, frontal balding, and EKG changes. The discovery that the genetic defect is an amplified trinucleotide repeat in the 3-prime untranslated region of a protein kinase gene on chromosome 19 explains many of the unusual features of this disorder. Problems can range from very mild to very severe even within the same family, and it is not always obvious who in the family has the gene alteration. Severity varies with the number of repeats: normal individuals have from 5 to 30 repeat copies; mildly affected pe