DMPK and myotonic dystrophy type 1: DM1 is the most common type of adult-onset muscular dystrophy worldwide (affecting 1 in 8000) (Harper, 2001), and is caused by a CTG triplet repeat expansion within the 3′ untranslated region (UTR) of the dystrophia myotonica protein kinase (DMPK) gene on chromosome 19 q13.3 (Mahadevan et al., 1992).