Increased inclusion of the alternative exon 7a (E7a) in Clcn1 transcripts in DM1 causes a frameshift that leads to a premature termination codon (PTC), and thus a non-functional truncated ion channel as well as non-sense mediated decay (NMD) of the mRNA4. Here, CLCN1 is linked to myotonic dystrophy type 1.