Periodic paralysis, myotonia congenita and sarcolemmal ion channels: a success of the candidate gene approach.

The classification of periodic paralyses and myotonic syndromes has been a subject of debates for the last 40 yr. Recent advances in molecular biology have led geneticists to reconsider this old question, using a candidate gene approach. Two groups of disorders have now emerged: (1) muscle sodium channel-associated diseases which include hyperkalemic periodic paralysis and its clinical variants, as well as paramyotonia congenita; (2) muscle chloride channel-associated disorders which comprise both the dominant and recessive form of myotonia congenita. This review is focussed on these recent discoveries.