Potassium-aggravated myotonia is a disorder that affects muscles used for movement (skeletal muscles). Beginning in childhood or adolescence, people with this condition experience bouts of sustained muscle tensing (myotonia) that prevent muscles from relaxing normally. Myotonia causes muscle stiffness that worsens after exercise and may be aggravated by eating potassium-rich foods such as bananas and potatoes. Stiffness occurs in skeletal muscles throughout the body. Potassium-aggravated myotonia ranges in severity from mild episodes of muscle stiffness to severe, disabling disease with frequent attacks. Unlike some other forms of myotonia, potassium-aggravated myotonia is not associated with episodes of muscle weakness.
This condition appears to be rare; it has been reported in only a few individuals and families worldwide.
Mutations in the SCN4A gene cause potassium-aggravated myotonia.
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 normally, 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.
Mutations 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. The influx of extra sodium ions triggers prolonged muscle contractions, which are the hallmark of myotonia.
Potassium-aggravated myotonia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits a mutation in the SCN4A gene from one affected parent. Other cases result from new mutations in the gene. These cases occur in people with no history of the disorder in their family.
Other Names for This Condition
- sodium channel myotonia
Additional Information & Resources
Genetic Testing Information
Genetic and Rare Diseases Information Center
Research Studies from ClinicalTrials.gov
Catalog of Genes and Diseases from OMIM
Scientific Articles on PubMed
- Colding-Jørgensen E, Duno M, Vissing J. Autosomal dominant monosymptomatic myotonia permanens. Neurology. 2006 Jul 11;67(1):153-5. Citation on PubMed
- Lerche H, Heine R, Pika U, George AL Jr, Mitrovic N, Browatzki M, Weiss T, Rivet-Bastide M, Franke C, Lomonaco M, et al. Human sodium channel myotonia: slowed channel inactivation due to substitutions for a glycine within the III-IV linker. J Physiol. 1993 Oct;470:13-22. Citation on PubMed or Free article on PubMed Central
- Orrell RW, Jurkat-Rott K, Lehmann-Horn F, Lane RJ. Familial cramp due to potassium-aggravated myotonia. J Neurol Neurosurg Psychiatry. 1998 Oct;65(4):569-72. Citation on PubMed or Free article on PubMed Central
- Ptáĉek LJ, Tawil R, Griggs RC, Meola G, McManis P, Barohn RJ, Mendell JR, Harris C, Spitzer R, Santiago F, et al. Sodium channel mutations in acetazolamide-responsive myotonia congenita, paramyotonia congenita, and hyperkalemic periodic paralysis. Neurology. 1994 Aug;44(8):1500-3. Citation on PubMed
- Vicart S, Sternberg D, Fontaine B, Meola G. Human skeletal muscle sodium channelopathies. Neurol Sci. 2005 Oct;26(4):194-202. Review. Citation on PubMed