Normokalemic periodic paralysis (NPP) is a rare genetic disorder characterized by recurrent episodes of muscle weakness or paralysis, typically causing temporary immobility. The term "normokalemic" refers to the fact that during an episode, the blood potassium level remains within the normal range. This distinguishes it from other forms of periodic paralysis, such as hypokalemic periodic paralysis where levels of potassium in the blood drop significantly during an attack.
NPP is usually inherited in an autosomal dominant manner, meaning that an affected individual has a 50% chance of passing on the gene mutation to each of their children. The precise genetic mutations causing NPP have been identified in several ion channel genes that regulate muscle cell function.
Attacks of muscle weakness or paralysis in NPP can vary in frequency, duration, and severity, with some individuals experiencing them only occasionally and others more frequently. The episodes can be triggered by various factors, including exercise, fasting, certain medications, or even changes in temperature. The attacks typically begin in childhood or adolescence, but can also manifest in adulthood.
During an attack, individuals with NPP may experience muscle weakness, flaccidity, and difficulty moving. The episodes can affect various muscle groups in the body, including the limbs, face, and trunk. Typically, the attacks are temporary and resolve spontaneously, often lasting minutes to hours.
Treatment for NPP mainly involves managing and preventing attacks. This may involve avoiding triggers, such as extreme temperatures or strenuous exercise, and using medications to help prevent or shorten the duration of episodes. Genetic counseling is also important for affected individuals and their families to understand the risks and inheritance patterns associated with NPP.
