DMPK and myotonic dystrophy type 1: DM1 is an autosomal dominant disease caused by unstable expanded cytosine–thymine–guanine (CTG) repeats within the 3′ untranslated region (3′ UTR) of the DMPK (Dystrophia Myotonica Protein Kinase; OMIM* 605377) gene at chromosome 19q13.3 [2,3,4,5].