[Periodic paralysis, myotonia]

Certain muscular disorders with functional abnormalities as their major clinical features have been considered to be attributable to disturbance of the membrane transport system. Among such diseases, myotonia congenita was first detected to have decreased chloride conductance in 1960s, and muscle chloride channel localized in chromosome 7q was confirmed to be the genetic site of the lesion in 1992. As for hyperkalemic and normokalemic periodic paralysis, paramyotonia congenita, and adynamia episodica hereditaria, genetic abnormalities of muscle sodium channel in chromosome 17 was proven in 1990, though electrophysiologically this possibility has been strongly suggested since 1983. A concept of sodium channelopathy was proposed for these diseases with abnormal sodium channel, and, additional third type of such disorders was reported in which only fluctuating myotonia is the main symptom.