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Hyperkalemic periodic paralysis is a condition that causes episodes of extreme muscle weakness, usually beginning in infancy or early childhood. Most often, these episodes involve a temporary inability to move muscles in the arms and legs. Episodes tend to increase in frequency until about age 25, after which they may occur less frequently. Factors that can trigger attacks include rest after exercise, potassium-rich foods, stress, fatigue, and periods without food (fasting). Muscle strength improves between attacks, although many affected people continue to experience mild stiffness (myotonia), particularly in muscles of the face and hands.
Some people with hyperkalemic periodic paralysis have increased levels of potassium in their blood (hyperkalemia) during attacks. In other cases, attacks are associated with normal blood potassium levels (normokalemia). Ingesting potassium can trigger attacks in affected individuals, even if blood potassium levels do not go up.
Hyperkalemic periodic paralysis affects an estimated 1 in 200,000 people.
Mutations in the SCN4A gene cause hyperkalemic periodic paralysis.
The SCN4A gene provides instructions for making a protein that plays an essential role in muscles used for movement (skeletal muscles). For the body to move normally, these muscles must tense (contract) and relax in a coordinated way. Muscle contractions are triggered by the flow of certain positively charged atoms (ions), including sodium, into 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 the flow of sodium ions into muscle cells, which reduces the ability of skeletal muscles to contract. Because muscle contraction is needed for movement, a disruption in normal ion transport leads to episodes of muscle weakness or paralysis.
Changes in this gene are associated with hyperkalemic periodic paralysis.
This condition 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 most cases, an affected person has one parent with the condition.
These resources address the diagnosis or management of hyperkalemic periodic paralysis and may include treatment providers.
You might also find information on the diagnosis or management of hyperkalemic periodic paralysis in Educational resources (http://www.ghr.nlm.nih.gov/condition/hyperkalemic-periodic-paralysis/show/Educational+resources) and Patient support (http://www.ghr.nlm.nih.gov/condition/hyperkalemic-periodic-paralysis/show/Patient+support).
General information about the diagnosis (http://ghr.nlm.nih.gov/handbook/consult/diagnosis) and management (http://ghr.nlm.nih.gov/handbook/consult/treatment) of genetic conditions is available in the Handbook. Read more about genetic testing (http://ghr.nlm.nih.gov/handbook/testing), particularly the difference between clinical tests and research tests (http://ghr.nlm.nih.gov/handbook/testing/researchtesting).
To locate a healthcare provider, see How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.
You may find the following resources about hyperkalemic periodic paralysis helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines (http://ghr.nlm.nih.gov/ConditionNameGuide) and How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.
Ask the Genetic and Rare Diseases Information Center (http://rarediseases.info.nih.gov/GARD/).
autosomal ; autosomal dominant ; cell ; contraction ; familial ; fasting ; gene ; hyperkalemia ; ions ; ion transport ; myotonia ; potassium ; protein ; sodium ; stress
You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://www.ghr.nlm.nih.gov/glossary).
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.