The disorder is caused by mutations in part of a gene (CLCN1) encoding the ClC-1 chloride channel, resulting in muscle fiber membranes having an unusually exaggerated response to stimulation (hyperexcitability). Three cases have been reported who were diagnosed with Thomsen's<unk>  and proved on genetic testing not to have mutations in the chloride gene but rather in the alpha-subunit of the voltage gated sodium channel (SCN4A). Like chloride channel mutations, patients with sodium channel mutations may have a very varied phenotype, making a diagnosis more difficult.
Myotonia congenita
Myotonic dystrophy
Paramyotonia congenita
Periodic paralysis
Klumpke paralysis
Quadrigia
Cardiofaciocutaneous syndrome
Hyperkalemic periodic paralysis