Hyperkalemic periodic paralysis is an inherited disease of Quarter Horses. At least one of the parents of an affected animal must also carry the gene and/or be affected, but not necessarily both because this is a dominant condition and only one abnormal gene need be present. HYPP is characterized by intermittent attacks of muscle weakness, which can appear as muscle tremors, weakness, disorientation, or convulsions. Attacks frequently occur suddenly, like a seizure, choking, or colic-like symptoms and may resolve just as quickly.

Diagnosis of HYPP can be made from a blood sample by the identification of the gene using molecular techniques. Because the disease is genetic, there is no cure; however, management of the diet and in some cases medication may prevent clinical manifestation of the disease in a positively tested horse.