DMPK and myotonic dystrophy type 1: DM1, also known as Steinert disease, is caused by the abnormal expansion of a CTG-trinucleotide repeat in the 3′-UTR of the dystrophia myotonic protein kinase (DMPK) gene (Brook et al., 1992; Fu et al., 1992; Mahadevan et al., 1992).