DMPK and myotonic dystrophy type 1: DM1 is an autosomal dominant disorder that results from expansion of a non-coding CTG repeat in the 3′ untranslated region of the DMPK gene on chromosome 19 (Aslanidis et al., 1992; Brook et al., 1992; Harley et al., 1992; Mahadevan et al., 1992).