Several important human diseases are associated with expansion of polynucleotide sequences, in most cases trinucleotide repeats. Myotonic dystrophy (DM1) is one of these diseases, and is associated with increases in the number of CTG repeats in the 3' UTR of the gene encoding myotonin (a.k.a. DM Kinase, DMK or myotonin-Protein Kinase), a ser/thr kinase expressed specifically in muscle. Mammalian genomes contain three muscleblind-like proteins, generally referred to as MBNL1, MBNL2 and MBNL3, and all three were found to associate with long double stranded CUG RNA repeats, thus, being triplet repeat expansion dsRNA-binding proteins.