Expansion of a CTG repeat in the 3' UTR of the DMPK gene causes myotonic dystrophy type 1 (DM1) and the expansion of a CCTG repeat in intron 1 of the ZNF9 gene causes myotonic dystrophy type 2 (DM2). The gene discussed is DMPK; the disease is myotonic dystrophy type 2.