Myotonic dystrophy type 1 (DM1; MIM #160900), the most frequent autosomal dominant myopathy in adults, is associated with an expansion of (CTG)n repetitions in the 3'UTR of the DMPK gene (DMPK; MIM#605377), on chromosome 19q13.3 [1-3]. This evidence concerns the gene DMPK and myotonic dystrophy type 1.