Hyperkalemic periodic paralysis (Hyperkalemic periodic paralysis) - Gen SCN4A
Hyperkalemic periodic paralysis is a disease that causes episodes of extreme muscle weakness or paralysis. Usually the disease manifests in infancy or early childhood. Often these episodes involve a temporary inability to move the muscles in the arms and legs. These episodes tend to increase in frequency until mid-adulthood, after which occur less frequently. Factors that can trigger these attacks include rest after exercise, potassium - rich foods such as bananas and potatoes, stress, fatigue, alcohol, pregnancy, exposure to cold temperatures, certain medications and periods fasting. Muscle strength returns to normal between episodes, although many people continue expressing myotonia, especially in the muscles of the face and hands.
Most of those affected have hyperkalemia during episodes. Hyperkalemia occurs when weak or paralyzed muscles release of potassium ions into the bloodstream. In other cases, the episodes are associated with potassium concentrations in normal blood. Potassium intake can cause episodes in affected individuals, even if potassium levels in the blood do not increase.
This process is due to mutations in the gene SCN4A (sodium voltage-gated channel alpha subunit 4), located on the long arm of chromosome 17 (17q23.3). This gene encodes the alpha subunit of sodium channels, which play an essential role in skeletal muscles. In order for the body to move normally, these muscles must contract and relax in a coordinated manner. One change that helps muscle contractions is the flow of ions, including sodium, in muscle cells. Channels formed with protein SCN4A control the flow of sodium ions in these cells.
There are more than 10 mutations in the gene SCN4A in people with periodic paralysis Hyperkalemic. Mutations in the gene SCN4A alter the usual structure and function of sodium channels in skeletal muscle cells. Altered channels remain open long or remain closed long enough, allowing more sodium ions flow into muscle cells. This increase of sodium ions causes the release of potassium from the muscle cells, which causes the flow of sodium ions in these cells was further stimulated. These changes in ion transport reduce the ability of skeletal muscles to contract, leading to episodes of muscle weakness or paralysis. Between 30% and 40% of cases, the cause of the disease is unknown. It is likely that changes in other genes that have not been identified, are responsible for the disease in these cases.
This disease is inherited as an autosomal dominant, which means that a copy of the altered gene in each cell is sufficient to express the disease. In most cases, an affected person has a parent with the disorder.
Tests in IVAMI: in IVAMI perform detection of mutations associated with hyperkalemic periodic paralysis, by complete PCR amplification of exons SCN4A gene, and subsequent sequencing.
Samples recommended: EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample).