Alternative exons 6b and 7a of the skeletal muscle-specific chloride channel ClC-1 are aberrantly included in DM1 skeletal muscle where CELF1 levels are elevated [9], but are 100% skipped in normal muscle and do not respond to further loss of CELF activity in Myo-CELFΔ mice (data not shown). This evidence concerns the gene CEBPD and myotonic dystrophy type 1.