DMPK and myotonic dystrophy type 1: For example, in myotonic dystrophy type 1 (DM1), an expanded CUG repeat (CUGexp) in the 3′ UTR of the DM Protein Kinase (DMPK) transcript disrupts splicing regulator proteins in the muscleblind-like (MBNL) family, causing abnormal splicing of a number of pre-mRNAs2,3.