Mutations in a chloride channel (CLCN1) and in apamin-sensitive potassium channels are linked to myotonia in DM1 patients, as is the misregulated splicing of the calcium channel Cav1.1.8, 9, 10 Splicing errors in Cav1.1 channels are associated with increased central nucleation and muscle weakness in DM1 patients and mouse models. The gene discussed is CACNA1S; the disease is myotonic dystrophy type 1.