There are two genetically distinct types, DM1 and DM2, which are caused by similar noncoding repeat expansions in different genes: a (CTG)n expansion in the 3′ UTR of the DM1 protein kinase (DMPK) gene in DM1; and a (CCTG)n expansion in the first intron of the CCHC-type zinc finger nucleic acid binding protein (CNBP) gene [also known as zinc finger protein 9 (ZNF9)] in DM2 (La Spada and Taylor, 2010; Udd and Krahe, 2012; Timchenko, 2013; Thornton, 2014). Here, DMPK is linked to myotonic dystrophy type 2.