Hyperkalemic periodic paralysis
is a genetic condition that causes episodes of extreme muscle weakness, usually beginning in infancy or early childhood. Most often, these episodes involve a temporary inability to move muscles in the arms and legs. Episodes tend to increase in frequency until about age 25, after which they may occur less frequently. Factors that can trigger attacks include rest after exercise, potassium-rich foods, stress, fatigue, and long periods without food. Muscle strength improves between attacks, although many affected people continue to experience mild stiffness, particularly in muscles of the face and hands. This condition is caused by mutations in the SCN4A gene and is inherited in an autosomal dominant fashion. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.