Other Names: HOKPP; HypoPP

Hypokalemic periodic paralysis (HOKPP) is characterized by episodes of muscle paralysis associated with a fall in blood potassium levels (hypokalemia). Episodes typically involve a temporary inability to move muscles in the arms and legs. The first attack usually occurs in childhood or adolescence. Attacks can last for hours or days, and the frequency of attacks varies among people with HOKPP. The frequency is usually highest between the ages of 15 and 35, and then decreases with age. Some people with HOKPP also develop late-onset proximal myopathy.

HOKPP can be caused by mutations in the CACNA1S, SCN4A, or KCNJ18 gene. Inheritance is autosomal dominant. Treatment varies depending on the intensity and duration of attacks. Minor attacks may go away on their own, while treatment for moderate or severe attacks may involve taking potassium salts or intravenous (IV) potassium.

HOKPP is characterized by attacks of muscle weakness or loss of muscle movement (paralysis) that come and go. The weakness or paralysis is most commonly located in the shoulders and hips, affecting the muscles of the arms and legs. Muscles of the eyes and those that help you breathe and swallow may also be affected. While muscle strength is usually regained between attacks, repeated episodes can lead to persistent muscle weakness later in life.

Attacks usually begin in childhood or adolescence, and the frequency of attacks varies. Some people have attacks every day, while others have them once a year. Attacks usually last at least a few hours, to sometimes days. Attacks can occur without warning or they may be triggered by factors such as carbohydrate-rich meals and rest after exercise.

HOKPP can be caused by mutations in any of at least 3 known genes: CACNA1S, SCN4A, or KCNJ18. All three of these genes give the body instructions to make parts of ion channels that are primarily expressed in skeletal muscle cells. Muscle contractions are triggered by the flow of ions into muscle cells. Mutations that cause HOKPP affect the usual structure or function of ion channels, impairing their ability to regulate the flow of ions into muscle cells. This, in turn, reduces the ability of skeletal muscles to contract, causing the weakness and paralysis associated with HOKPP.

Not all people with a clinical diagnosis of HOKPP are found to have a mutation in one of the genes mentioned above. This suggests that other, yet unidentified genes may also be responsible for the condition.

Contact the Genetic and Rare Diseases (GARD) Information Center for more information on Hypokalemic periodic paralysis.