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Ancestor membership does not transfer phenotype values between groups.","importantHtml":""},"sections":[{"bodyHtml":"<p>Potassium-aggravated myotonia is caused by variants (also known as mutations) in the SCN4A gene. The SCN4A gene provides instructions for making a protein that is critical for the normal function of skeletal muscle cells. For the body to move, skeletal muscles must tense (contract) and relax in a coordinated way. Muscle contractions are triggered by the flow of positively charged atoms (ions), including sodium, into skeletal muscle cells. The SCN4A protein forms channels that control the flow of sodium ions into these cells.</p><p>Variants in the SCN4A gene alter the usual structure and function of sodium channels. The altered channels cannot properly regulate ion flow, increasing the movement of sodium ions into skeletal muscle cells. When excess potassium is present in the body, which occurs after eating potassium-rich foods, even more sodium ions flow into skeletal muscle cells in order to maintain a proper balance of calcium and potassium. The influx of extra sodium ions triggers prolonged muscle contractions, which are characteristic of myotonia.</p><p class=\"section-source\"><a href=\"https://medlineplus.gov/genetics/condition/potassium-aggravated-myotonia/#causes\">MedlinePlus Genetics: Causes</a></p>","key":"forms","title":"What causes Potassium-aggravated myotonia?"},{"bodyHtml":"<p>Potassium-aggravated myotonia ranges in severity from mild episodes of muscle stiffness (myotonia fluctuans) to severe, disabling disease with frequent attacks (myotonia permanen). Unlike some other forms of myotonia, potassium-aggravated myotonia is not associated with episodes of muscle weakness.</p><p class=\"section-source\">Source: <a href=\"https://medlineplus.gov/genetics/condition/potassium-aggravated-myotonia\">MedlinePlus Genetics</a></p>","key":"overview","title":"Condition overview"}],"sharedSources":[],"slug":"potassium-aggravated-myotonia","sourceDocuments":[{"name":"Potassium-aggravated myotonia","reviewed":"2007-04","sections":{"causes":{"fetchedAt":"2026-10-20T20:24:19.700225+00:00","label":"Causes","pageSha256":"7941efe5175c20741cd77a98cf6c9a34c1f2b1ea8bff52b398bfe3982d81c577","sourceUrl":"https://medlineplus.gov/genetics/condition/potassium-aggravated-myotonia/#causes","status":"available"}},"source_release":"2026-10-01","url":"https://medlineplus.gov/genetics/condition/potassium-aggravated-myotonia"}],"sourceNote":"MedlinePlus descriptions and Causes; original HPO annotations.","takeawayHtml":"Cause explanations are from MedlinePlus Genetics. Feature values below retain their original sources and patient groups.","title":"Potassium-aggravated myotonia"},"schemaVersion":1}