[Periodic paralysis: new pathophysiological aspects]

Periodic paralyses are neuromuscular disorders characterized by attacks of muscle weakness coinciding with changes in blood potassium levels. They are thus classified as hypokalaemic, normokalaemic or hyperkalaemic. Most forms are genetic, with autosomal dominant inheritance. These diseases are channelopathies, i.e. caused by mutations in ion channel genes. The culprit genes encode muscle sodium, calcium and potassium channels. Mutations in calcium or potassium channels cause periodic paralyses of the same type (hypokalaemic periodic paralysis or Andersen-Tawil Syndrome). In contrast, distinct mutations in the gene encoding the sodium channel can cause the entire range of periodic paralysis (hypokalaemic, normokalaemic or hyperkalaemic). The physiological consequences of mutations have been studied with patch-clamp techniques and electromyography. Generally speaking, mutations alter the excitability cycle of the muscle membrane, resulting in a loss of function (paralysis). Electromyographic studies have demonstrated a good correlation between symptoms and physiological parameters, giving rise to a classification that can help orient the molecular diagnosis. Work on the genetics and pathophysiology of periodic paralyses has helped to improve the diagnosis and management of these syndromes.