DM1 is caused by unstable trinucleotide (CTG) repeat expansion in the 3′ untranslated region on the dystrophia myotonia-protein kinase (DMPK) gene, and type 2 DM (DM2) is caused by a tetranucleotide (CCTG) repeat expansion in intron 1 of the zinc finger 9 (ZNF9) gene [1]. Here, DMPK is linked to myotonic dystrophy type 1.