Hyperkalemic periodic paralysis
From Wikipedia, the free encyclopedia
| ICD-9 | 359.3 |
|---|---|
| OMIM | 170500 |
| DiseasesDB | 6252 |
| MeSH | D020513 |
Hyperkalemic periodic paralysis (HYPP), also known as Impressive Syndrome, is an inherited autosomal dominant disorder which affects sodium channels in muscle cells and the ability to regulate potassium levels in the blood. It is most commonly associated with horses, but also occurs in humans.
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[edit] Disease in horses
[edit] Symptoms and presentation
This inherited disease is characterized by uncontrollable muscle twitching and substantial muscle weakness or paralysis among affected horses. HYPP is a dominant disorder; therefore heterozygotes bred to genotypically normal horses will still likely produce clinically affected offspring 50% of the time.
[edit] Inheritance and prevalence
Horses affected with HYPP can be treated with some possibility of reducing symptoms, but the degree that medical treatment helps varies from horse to horse. Therefore, horses with HYPP should only be ridden by experienced riders, if anyone, because episodes of paralysis can come on very suddenly and a rider has to be extremely alert to recognize an impending episode which may cause the horse to lose control of its body.
The disease is most common in the bloodline of the famous Appendix American Quarter Horse stallion Impressive, who has over 55,000 living descendants as of 2003. Although the disease is primarily limited to the American Quarter Horse breed and closely related breeds such as American Paint Horses and Appaloosas at this time, cross-breeding has begun to extend it to grade horses and ponies. The spread of the disease is perpetuated by the favorable judgings given to diseased horses in showing, due to the extreme extra large, bulky muscles the N/H and H/H horses carry, (as opposed to the N/N horses), that judges favor.
[edit] Genetics
In 1994, researchers at the University of Pittsburgh, with a grant from various horse organizations, isolated the genetic mutation responsible for the problem and developed a blood test for it. Using this test, horses may be identified as:
- H/H, meaning they have the mutation and it is homozygous. These horses always pass on the disease.
- N/H, meaning they have the mutation and it is heterozygous. These horses are affected to a lesser degree, and pass on the disease 50% of the time.
- N/N, meaning they do not have the mutation and cannot pass it on, even if they are descendants of Impressive.
[edit] Regulation
Recently, horse organizations have begun instituting rules to attempt to eliminate this widespread disease. The American Quarter Horse Association (AQHA) now mandates testing for the "Impressive" mutation and will no longer register homozygous (H/H) foals as of 2007, with discussion of heterozygous (N/H) foals pending. The Appaloosa Association will no longer accept homozygous foals as of 2008. It is believed that both primary palomino registries will exclude any foal carrying the "Impressive" mutation as of 2007. The main organization affected by HYPP that has not yet taken action is the American Paint Horse Association (APHA), although many other smaller organizations are also affected.
[edit] Disease in humans
Although much rarer, hyperkalemic periodic paralysis has also been observed in humans. The most common underlying cause is one of several possible point mutations in the genes synthesising calcium or sodium ion channels in skeletal muscle; these mutations can either be inherited in an autosomal dominant or recessive manner.
