Hyperklermik Periodic Paralaysis (HYPP)

Hyperkalemic Periodic Paralysis Disease (HYPP) is a muscular disease that affects both horses and humans. Symptoms of HYPP may include muscle twitching, unpredictable paralysis attacks which can lead to sudden death, and respiratory noises. Severity of attacks varies from unnoticeable to collapse or sudden death. The cause of death is usually respiratory failure and/or cardiac arrest.

The HYPP gene is dominant so both homozygous positive (HH) and heterozygous (nH) will cause this muscular disorder. Only homozygous negative (nn) has no HYPP effect. Since HYPP is dominant, the effects of it can also be transposed to other species of horses when intermixing occurs. This makes the recognition and elimination of this disorder very important in preserving the inherited health of all horses.

In horses, HYPP has been traced back to one horse named Impressive and has the alternative name, Impressive Syndrome, named after this horse.