Classical DM, called Steinert's disease or myotonic dystrophy type 1 (DM1), has been associated with the presence of an abnormal expansion of a CTG trinucleotide repeat on chromosome 19q13.3 [2] in the DMPK gene that codes for myotonic dystrophy protein kinase, a protein mainly expressed in smooth, cardiac, and skeletal muscle cells [3]. The gene discussed is DMPK; the disease is myotonic dystrophy type 1.