DM1 and DM2 are respectively caused by the aberrant insertion of CTG and CCTG expansion repeats in the 3′ untranslated region (UTR) of dystrophin myotonic protein kinase (DMPK) [41] and in the first intron of zinc-finger protein 9 (ZNF9) [42]. The gene discussed is DMPK; the disease is myotonic dystrophy type 2.