|http://ghr.nlm.nih.gov/ A service of the U.S. National Library of Medicine®|
The official name of this gene is “sodium channel, voltage-gated, type IV, alpha subunit.”
SCN4A is the gene's official symbol. The SCN4A gene is also known by other names, listed below.
The SCN4A gene belongs to a family of genes that provide instructions for making sodium channels. These channels, which transport positively charged sodium atoms (sodium ions) into cells, play a key role in a cell's ability to generate and transmit electrical signals.
The SCN4A gene provides instructions for making sodium channels that are abundant in muscles used for movement (skeletal muscles). For the body to move normally, these muscles must tense (contract) and relax in a coordinated way. Muscle contractions are triggered by the flow of certain ions, including sodium, into muscle cells. Channels made with the SCN4A protein control the flow of sodium ions into these cells.
The SCN4A gene belongs to a family of genes called SCN (sodium channels).
A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genefamilies) in the Handbook.
More than 10 mutations in the SCN4A gene are responsible for hyperkalemic periodic paralysis. Each of these mutations changes a single building block (amino acid) in the SCN4A protein, which alters the structure and function of sodium channels in skeletal muscle cells. These changes delay the closing of channels made with the SCN4A protein or prevent the channels from staying closed. As a result, sodium ions continue flowing into muscle cells abnormally. Muscles with sustained high levels of sodium ions are unable to contract, resulting in attacks of muscle weakness.
At least six mutations in the SCN4A gene have been identified in people with hypokalemic periodic paralysis. These genetic changes are responsible for about 10 percent of all cases of this condition. Each of the known mutations changes a single amino acid in the SCN4A protein, which alters the structure and function of sodium channels in skeletal muscle cells. The channels close too quickly, reducing the flow of sodium ions into muscle cells. This disruption in ion transport prevents muscles from contracting normally. Because muscle contraction is needed for movement, reduced sodium ion flow into muscle cells leads to episodes of severe muscle weakness or paralysis.
At least 13 mutations in the SCN4A gene are known to cause paramyotonia congenita. These mutations each change a single amino acid in the SCN4A protein, which alters the structure and function of sodium channels in skeletal muscle cells. The most common genetic changes replace the amino acid arginine with one of several other amino acids at protein position 1448.
Mutations delay the closing of channels made with the SCN4A protein and, once the channels are closed, cause them to open again too quickly. These changes increase the flow of sodium ions into skeletal muscle cells. An influx of extra sodium ions triggers prolonged muscle contractions, which underlie the episodes of muscle stiffness (myotonia) characteristic of paramyotonia congenita. Muscles with sustained high levels of sodium ions may become unable to contract at all, resulting in attacks of muscle weakness.
The effects of SCN4A mutations on the altered ion channels may be exacerbated by cold temperatures, which may help explain why signs and symptoms can be induced by exposure to cold.
Several mutations in the SCN4A gene cause potassium-aggravated myotonia. The most common genetic changes replace the amino acid glycine with one of several other amino acids at protein position 1306. These mutations delay the closing of channels made with the SCN4A protein, which increases the flow of sodium ions into skeletal muscle cells. An influx of extra sodium ions triggers prolonged muscle contractions, which underlie the muscle stiffness characteristic of potassium-aggravated myotonia.
A mutation in the SCN4A gene is also responsible for one form of congenital myasthenic syndrome, a muscle disorder that appears shortly after birth. People with this disorder have general muscle weakness and recurrent attacks of paralysis that specifically affect muscles used for speaking and breathing. The SCN4A mutation associated with this condition replaces the amino acid valine with the amino acid glutamic acid at protein position 1442 (written as Val1442Glu or V1442E). This genetic change alters the structure and function of sodium channels in skeletal muscle cells. The channels close too quickly, reducing the flow of sodium ions into muscle cells. This disruption in ion transport interferes with normal muscle contraction, leading to muscle weakness and episodes of paralysis.
Cytogenetic Location: 17q23.3
Molecular Location on chromosome 17: base pairs 62,015,913 to 62,050,277
The SCN4A gene is located on the long (q) arm of chromosome 17 at position 23.3.
More precisely, the SCN4A gene is located from base pair 62,015,913 to base pair 62,050,277 on chromosome 17.
See How do geneticists indicate the location of a gene? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genelocation) in the Handbook.
You and your healthcare professional may find the following resources about SCN4A helpful.
You may also be interested in these resources, which are designed for genetics professionals and researchers.
See How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.
acids ; amino acid ; cell ; channel ; congenital ; contraction ; gene ; glycine ; ions ; ion transport ; mutation ; myotonia ; Na ; potassium ; protein ; skeletal muscle ; sodium ; sodium channel ; subunit ; syndrome ; voltage
You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://ghr.nlm.nih.gov/glossary).
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.