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The official name of this gene is “sodium channel, voltage-gated, type V, alpha subunit.”
SCN5A is the gene's official symbol. The SCN5A gene is also known by other names, listed below.
The SCN5A 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 SCN5A gene provides instructions for making a sodium channel that is abundant in heart (cardiac) muscle. These channels open and close at specific times to control the flow of sodium ions into cardiac muscle cells. By changing the electrical properties of these cells, sodium channels play a major role in signaling the start of each heartbeat, coordinating the contractions of the upper and lower chambers of the heart, and maintaining a normal heart rhythm.
The SCN5A 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 200 mutations in the SCN5A gene have been identified in people with Brugada syndrome, which is a heart condition characterized by an irregular heart rhythm (arrhythmia). SCN5A gene mutations also cause sudden unexpected nocturnal death syndrome (SUNDS), which was originally described in Southeast Asian populations. Researchers have since determined that SUNDS and Brugada syndrome are the same disorder.
Some SCN5A mutations change single protein building blocks (amino acids) in the SCN5A protein. These mutations alter the structure of ion channels made with the SCN5A protein and disrupt the flow of sodium ions into cardiac muscle cells. Other mutations prevent the SCN5A gene from producing any functional ion channels, which also reduces the inward flow of sodium ions. A disruption in ion transport changes the way the heart beats, leading to the arrhythmia often found in Brugada syndrome and SUNDS.
More than 100 mutations in the SCN5A gene are known to cause Romano-Ward syndrome, often called long QT syndrome. This condition causes the heart (cardiac) muscle to take longer than usual to recharge between beats, which can lead to arrhythmia.
The SCN5A gene mutations that cause Romano-Ward syndrome include changes in single amino acids and deletions or insertions of a small number of amino acids in the SCN5A protein. Channels made with these altered SCN5A proteins stay open longer than usual, which allows sodium ions to continue flowing into cardiac muscle cells abnormally. This delay in channel closure alters the transmission of electrical signals in the heart, increasing the risk of an irregular heartbeat that can cause fainting (syncope) or sudden death.
At least 10 mutations in the SCN5A gene have been found to cause another heart condition called sick sinus syndrome. This condition affects the function of the sino-atrial (SA) node, which is an area of specialized cells in the heart that functions as a natural pacemaker. The SCN5A gene mutations that cause sick sinus syndrome lead to the production of nonfunctional sodium channels or abnormal channels that cannot transport ions properly. The flow of these ions is essential for creating the electrical impulses that start each heartbeat and spread these signals to other areas of the heart. Mutations reduce the flow of sodium ions, which alters the SA node's ability to create and spread electrical signals. These changes increase the risk of abnormally fast or slow heartbeats, which can cause dizziness, light-headedness, syncope, and related symptoms.
Variations in the SCN5A gene are associated with several other heart conditions. These include familial heart block, which is an abnormality of the heart's electrical system that increases the risk of syncope and sudden death; dilated cardiomyopathy, which weakens and enlarges the heart; and potentially life-threatening forms of arrhythmia called atrial fibrillation and ventricular fibrillation. The genetic variations associated with these conditions alter the flow of sodium ions through the channel, which can lead to abnormal heart rhythms and affect the heart's ability to pump blood.
SCN5A gene mutations have also been identified in some cases of sudden infant death syndrome (SIDS). SIDS is a major cause of death in babies younger than 1 year. It is characterized by sudden and unexplained death, usually during sleep. Researchers are working to determine how changes in the SCN5A gene could contribute to SIDS. Other genetic and environmental factors, many of which have not been identified, also play a part in determining the risk of this disorder.
Certain drugs, including medications used to treat arrhythmias, infections, seizures, and psychotic disorders, can lead to an abnormal heart rhythm in some people. This drug-induced heart condition, which is known as acquired long QT syndrome, increases the risk of cardiac arrest and sudden death. A small percentage of cases of acquired long QT syndrome occur in people who have an underlying change in the SCN5A gene.
Cytogenetic Location: 3p21
Molecular Location on chromosome 3: base pairs 38,548,061 to 38,649,672
The SCN5A gene is located on the short (p) arm of chromosome 3 at position 21.
More precisely, the SCN5A gene is located from base pair 38,548,061 to base pair 38,649,672 on chromosome 3.
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 SCN5A 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 ; arrhythmia ; atrial ; atrial fibrillation ; cardiac ; cardiac arrest ; cardiomyopathy ; cell ; channel ; dilated ; fainting ; familial ; fibrillation ; gene ; ions ; ion transport ; long QT syndrome ; muscle cells ; Na ; nocturnal ; pacemaker ; protein ; psychotic ; SA node ; sinus ; sodium ; sodium channel ; subunit ; syncope ; 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.