DMPK and myotonic dystrophy type 1: In 1992, Myotonic Dystrophy type 1 (DM1) was shown to be caused by an expanded [CTG]n repeat in the 3′-untranslated region of the DMPK gene (dystrophia myotonica-protein kinase) in the chromosomal region 19q13.3 [1–3].