Non-dystrophic myotonias (NDM) are rare muscle disorders caused by mutations in skeletal voltage-gated channels leading to delayed relaxation after voluntary contraction. They subdivided into sodium channelopathies, when the mutation is SCN4A gene, and chloride CLCN1 gene. Symptoms, which may differ according subtype, exacerbating factors, over disease course, can include stiffness, pain, fatig...