DMPK and myotonic dystrophy type 1: DM1 and DM2 are caused by a CTG expansion (50 to >3500) in the 3′UTR of the dystrophia myotonica protein kinase (DMPK) gene and by a CCTG expansion (75 to approximately 11000) in the first intron of the zinc finger protein 9 (ZNF9) gene, respectively (Ranum and Cooper, 2006; O’Rourke and Swanson, 2009; Thornton, 2014).