An autosomal dominant familial disorder which presents in infancy or childhood and is characterized by episodes of weakness associated with hyperkalemia. During attacks, muscles of the lower extremities are initially affected, followed by the lower trunk and arms. Episodes last from 15-60 minutes and typically occur after a period of rest following exercise. A defect in skeletal muscle sodium channels has been identified as the cause of this condition. Normokalemic periodic paralysis is a closely related disorder marked by a lack of alterations in potassium levels during attacks of weakness. (Adams et al., Principles of Neurology, 6th ed, p1481)

Synonyms: Paralysis, Hyperkalemic Periodic, Myotonic Periodic Paralysis, Gamstorp Episodic Adynamy, Hyperkalemic Periodic Paralysis, Hyperkaliemic Periodic Paralysis Type 2, Hyperkalemic Periodic Paralysis, Familial, Hyperkalemic Periodic Paralysis Type 2, Paralysis, Periodic, Hyperkalemic, Familial, Disease, Gamstorp, Primary Hyperkalemic Periodic Paralysis, Familial Hyperkalemic Periodic Paralysis, HyperKPP, HyperPP, Adynamia Episodica Hereditaria, Gamstorp Disease, Sodium Channel Muscle Disease, Adynamia Episodica Hereditaria with or without Myotonia