CELF1 and myotonic dystrophy type 1: In DM1, long CUG repeats lead to decreased MBNL1 activity and increased CELF1 activity in muscle cells, which results in mis-splicing events in different developmentally regulated genes including the insulin receptor (IR), the chloride channel (CLCN1) and the cardiac tropin T (TNNT2), which explain several aspects of DM1 symptomatology (Ranum and Cooper, 2006; Wheeler and Thornton, 2007).