DMPK and myotonic dystrophy type 1: DM1 [Online Mendelian Inheritance of Man (OMIM) 160900] has been identified as an autosomal-dominant disorder associated with the presence of an abnormal CTG trinucleotide repeat expansion in the 3′ untranslated region (UTR) of the gene encoding myotonic dystrophy protein kinase (DMPK) on chromosome 19.