DM1 causes progressive weakness in the face, neck, and distal limb muscles and is related to an expansion of an unstable CTG trinucleotide repeat at the 3′ untranslated region of the DMPK gene,17 while DM2 causes myotonia and muscle wasting and is caused by an expansion of the CCTG repeat of the CNBP gene.16 The gene discussed is DMPK; the disease is myotonic dystrophy type 1.