DMPK and myotonic dystrophy type 1: By positional cloning, the DM1 mutation associated with type 1 myotonic dystrophy was identified as a variable length polymorphism which resulted from increased number of trinucleotide CUG repeats in the 3′UTR of DM protein kinase (DMPK) expressed in tissues affected by myotonic dystrophy [115], [116].