[Molecular genetics of sodium channel myopathies]

The common molecular basis of hyperkalemic periodic paralysis, of paramyotonia congenita and that of myotonia fluctuans are the mutations of sodium channel SCN4A gene. The mutations result in an increased probability of channel openings at rest, or slightly decreased membrane potentials, and in delayed channel inactivation, both contributing either to myotonia or paralysis. Because of the lack of a sufficient amount of molecular genetic analyses of the above mentioned diseases, the precise clinical condition cannot be predicted according to the mutation position in the channel polypeptide as the same condition can be caused by mutations in different positions and, vice versa, mutations in the same position result in different clinical conditions. Causal therapy of these conditions is not known yet. (Fig. 1, Tab. 1, Ref. 47.)