DM1 (OMIM 160900) is an autosomal dominant muscular dystrophy that results from a trinucleotide CTG repeat expansion (50 – >5000 triplets) in the 3’-UTR of the Dystrophia Myotonica Protein Kinase gene (DMPK)7,8. The gene discussed is DMPK; the disease is myotonic dystrophy type 1.