Thursday, 21 November 2013
What is hyperkalemic periodic paralysis?
Hyperkalemic periodic paralysis is a condition that causes episodes of extreme muscle weakness or paralysis, 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 mid-adulthood, after which they occur less frequently. Factors that can trigger attacks include rest after exercise, potassium-rich foods such as bananas and potatoes, stress, fatigue, alcohol, pregnancy, exposure to cold temperatures, certain medications, and periods without food (fasting). Muscle strength usually returns to normal between attacks, although many affected people continue to experience mild stiffness (myotonia), particularly in muscles of the face and hands.
Most people with hyperkalemic periodic paralysis have increased levels of potassium in their blood (hyperkalemia) during attacks. Hyperkalemia results when the weak or paralyzed muscles release potassium ions into the bloodstream. 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.
How common is hyperkalemic periodic paralysis?
Hyperkalemic periodic paralysis affects an estimated 1 in 200,000 people.
What genes are related to hyperkalemic periodic paralysis?
Mutations in the SCN4A gene can 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. One of the changes that helps trigger muscle contractions is the flow of 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 stay open too long or do not stay closed long enough, allowing more sodium ions to flow into muscle cells. This increase in sodium ions triggers the release of potassium from muscle cells, which causes more sodium channels to open and stimulates the flow of even more sodium ions into these cells. These changes in ion transport reduce the ability of skeletal muscles to contract, leading to episodes of muscle weakness or paralysis.
In 30 to 40 percent of cases, the cause of hyperkalemic periodic paralysis is unknown. Changes in other genes, which have not been identified, likely cause the disorder in these cases.
Read more about the SCN4A gene.
How do people inherit 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.
Where can I find information about diagnosis or management of hyperkalemic periodic paralysis?
These resources address the diagnosis or management of hyperkalemic periodic paralysis and may include treatment providers.
- Gene Review: Hyperkalemic Periodic Paralysis Type
- Genetic Testing Registry: Familial hyperkalemic periodic
- Genetic Testing Registry: Hyperkalemic Periodic Paralysis Type
- Lab Tests Online:
- MedlinePlus Encyclopedia: Hyperkalemic Periodic
- Periodic Paralysis International: How is Periodic Paralysis
General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.
To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.
Where can I find additional information about hyperkalemic periodic paralysis?
Hyperkalemic periodic paralysis (HYPP, HyperKPP) is a genetic disorder that occurs in horses and humans, where it is also known as Impressive syndrome. It is aninherited autosomal dominant disorder that affects sodium channels in muscle cells and the ability to regulate potassium levels in the blood. It is most commonly associated with horses, but occurs in humans, where it may be called Gamstorp episodic adynamy. It is characterized by muscle hyperexcitability or weakness which, exacerbated by potassiumor cold, can lead to uncontrolled shaking followed by paralysis. Onset in humans usually occurs in early childhood.
The mutation which causes this disorder is dominant on SCN4A with linkage to thesodium channel expressed in muscle. The mutation causes single amino acid changes in parts of the channel which are important for inactivation. In the presence of high potassium levels, including those induced by diet, sodium channels fail to inactivate properly.