A tight regulation of membrane potential is necessary for myoblast fusion40 and potassium channels regulate the membrane potential of various cell types.13, 41 We therefore compared the membrane potential of normal and DM1 myoblasts by current clamp and detected no significant difference, with membrane potentials for both cell types around −60 mV (Supplementary Figure S3), as previously reported.12 The gene discussed is KCNA3; the disease is myotonic dystrophy type 1.