label: Potassium Aggravated Myotonia
label_lc: potassium aggravated myotonia
description: A group of autosomal dominant inherited non-dystrophic myotonias caused by mutations of the SCN4A gene, resulting in sodium muscle channelopathy. They are characterized by muscle stiffness, which worsens by ingestion of potassium-rich food.  This group includes myotonia fluctuans, myotonia permanens, and acetazolamide-responsive myotonia.