Hyperkalemic periodic paralysis

Hyperkalemic periodic paralysis (HYPP, HyperKPP) is a genetic disorder. It occurs in humans, horses (where it is also known as Impressive syndrome, after an index case in a horse named Impressive, or possibly one of his ancestors), and perhaps other animals. It is an inherited 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 potassium, heat or cold, can lead to uncontrolled shaking followed by paralysis. Onset in humans usually occurs in early childhood, but still occurs with adults.