Myotonic dystrophy type 1 (DM1) is an incurable neuromuscular disorder that is caused by an expanded CTG*CAG repeat in the 3′-untranslated region (3′ UTR) of the dystrophia myotonica-protein kinase (DMPK) gene (for a recent review, see ref. 1). This evidence concerns the gene DMPK and myotonic dystrophy type 1.