Myotonic dystrophy type 1 (DM1) is caused by (CTG)n repeat expansions in 3′ untranslated region of the dystrophia myotonica protein kinase (DMPK) gene, while myotonic dystrophy type 2 (DM2) is caused by a tetranucleotide repeat (CCTG)n in the first intron of the CCHC-type zinc finger, nucleic acid binding protein (CNBP) gene. This evidence concerns the gene DMPK and myotonic dystrophy type 1.