Hyperkalemic Periodic Paralysis in horses is an autosomal dominant inherited disease of the muscles. It is associated with episodic muscular paralysis and/or tremor which can lead to collapse and death of the animal.
HYPP is also known as ‘Impressive Syndrome’, due to its occurrence in offspring of the American stallion “Impressive”. Nowadays, the disease can be found in Quarter Horse, Paint, Appaloosa and US-Pony.
HYPP is caused by a point mutation in the genome of affected animals and leads to dysfunction of the sodium channels of muscle cells. Clinical symptoms of this defect are exaggerated and unintended contractions of the muscles. Such attacks can be stimulated by stress (transportation, convalescence, etc.) and high levels of potassium ions in the blood (low-potassium diet needs to be maintained). Heterozygous animals (h /H) frequently show milder symptoms than homozygous horses (H/H).
Genetic testing enables a clear distinction of affected homo- or heterozygous carriers (H/H and h/H, respectively) from healthy individuals (h/h) for diagnostic, treatment and mating objectives.