Myotonic dystrophy type 1 (DM1, Steinert’s disease; MIM #160900) is caused by a (CTG)n expansion in the 3′ UTR of the DMPK gene (MIM *605377) on chromosome 19q13.3, while myotonic dystrophy type 2 (DM2; MIM #602668) is caused by a (CCTG)n expansion in the first intron of CNBP (previously ZNF9) gene (MIM *116955), on chromosome 3q21.3 (Figure 1) [9,10]. The gene discussed is DMPK; the disease is myotonic dystrophy type 2.