Hyperkalemic Periodic Paralysis: The Impressive Syndrome

Hyperkalemic periodic paralysis, generally known as HYPP or Impressive Syndrome, has been wide-spread for several years now in Appaloosas, Quarter horses, Paints, and Palominos. Affected horses show well-developed muscles and are usually winning many halter classes. But, HYPP is not limited to just these stock breeds. It can cross over to any other breed if an affected horse is bred to one of a different breed which has yet to be affected. Impressive Syndrome was first identified in 1985 as a heritable disease of the muscle, which is caused by a genetic defect. Some humans have also been known to carry a rare disease very similar to this, called Eulenberg 's disease. HYPP causes muscle weakness or paralysis and is related to high potassium levels in the bloodstream. According to the Swedish National Board of Health and Welfare, "the cause of hyperkalemic periodic paralysis [in humans] is a change in a gene that regulates the production of a protein in the sodium ion channel of the skeletal muscle." These channels are affected by the defect in a way that they do not open and close properly; therefore sodium fluctuations cannot be controlled. When sodium fluxes are uncontrollable, the voltage current of the muscle cells changes, causing excess potassium to go to the bloodstream and the horse experiences periodic twitches and intense weakening of the muscles.

The oldest origin of this disease has yet to be found, but there is one horse from which we presently know it came from: the top-producing, top-winning Quarter horse stud, Impressive. This stallion was heavily muscled and won every halter class he was ever in. His owners soon found out after breeding him that he had another valuable trait: the ability to pass on his great conformation and musculature to his offspring. Horse breeders from all over wanted him as a stud, and that is why Impressive 's name shows up on so many of today 's papers for Quarters, Paints, and Appaloosas. Little did the breeders

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