Hyperkalemic Periodic Paralysis – HYPP

Hyperkalemic Periodic Paralysis (HYPP) in horses is characterized by sporadic episodes of muscle tremors (shaking or trembling), weakness, and sometimes collapse. The condition is caused by an autosomal incompletely dominant mutation in the sodium channel gene (SCN4A). The mutation in the SCN4A gene causes the sodium channels in the muscles to become “leaky,” leading to involuntary muscle contractions triggered by changes in blood potassium levels. These episodes can be induced by stress, fasting, or consuming high-potassium feeds, such as alfalfa.

The clinical signs of HYPP can vary widely and are influenced by factors such as stress, diet, and changes in exercise. Some horses may experience severe symptoms, while others show little to no signs of the disease. Affected horses often have significant muscle problems following exercise, including episodes of muscle twitching and shaking. In severe cases, horses may have difficulty swallowing or produce loud breathing noises, and sudden death can occur after a severe episode. Symptoms typically appear by two to three years of age.

Both homozygous and heterozygous horses can be affected, with homozygous horses generally exhibiting more severe symptoms. Between episodes, HYPP-affected horses may appear normal. Although there is no cure, most horses improve when dietary potassium levels are reduced and carefully managed.

Pubmed ID: 1338908

Year published: 1992

Omia ID: 785

Omia variant ID: