MBNL1 and myotonic dystrophy type 1: Sequestration of MBNL1 due to binding to expanded poly-CUG repeats in the dystrophia myotonica protein kinase (DMPK) mRNA is a main contributor to the pathogenesis of myotonic dystrophy type 1 (DM1), a syndrome characterized by muscle weakness, cardiac abnormalities, intellectual disability, and cataracts.