|http://ghr.nlm.nih.gov/ A service of the U.S. National Library of Medicine®|
The official name of this gene is “potassium channel, voltage gated KQT-like subfamily Q, member 2.”
KCNQ2 is the gene's official symbol. The KCNQ2 gene is also known by other names, listed below.
The KCNQ2 gene belongs to a large family of genes that provide instructions for making potassium channels. These channels, which transport positively charged atoms (ions) of potassium into and out of cells, play a key role in a cell's ability to generate and transmit electrical signals.
The specific function of a potassium channel depends on its protein components and its location in the body. Channels made with the KCNQ2 protein are active in nerve cells (neurons) in the brain, where they transport potassium ions out of cells. These channels transmit a particular type of electrical signal called the M-current, which prevents the neuron from continuing to send signals to other neurons. The M-current ensures that the neuron is not constantly active, or excitable.
Potassium channels are made up of several protein components (subunits). Each channel contains four alpha subunits that form the hole (pore) through which potassium ions move. Four alpha subunits from the KCNQ2 gene can form a channel. However, the KCNQ2 alpha subunits can also interact with alpha subunits produced from the KCNQ3 gene to form a functional potassium channel, and these channels transmit a much stronger M-current.
The KCNQ2 gene belongs to a family of genes called KCN (potassium 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.
A mutation in the KCNQ2 gene has been identified in most people with benign familial neonatal seizures (BFNS), a condition characterized by recurrent seizures (epilepsy) in newborn babies. The seizures begin around day 3 of life and usually go away within 1 to 4 months. More than 60 mutations in the KCNQ2 gene have been identified in families with this condition. Sometimes, the mutated protein never gets to the cell surface to form a channel, or the channel may be located in the wrong part of the neuron. Alternatively, the channel formed from the mutated protein may not function properly. As a result of these mutations, the M-current is reduced or altered, which leads to excessive excitability of neurons. Researchers believe that a reduction of the M-current by 25 percent is enough to cause BFNS. Seizures develop when neurons in the brain are abnormally excited. It is unclear why the seizures stop around the age of 4 months. It has been suggested that potassium channels formed from the KCNQ2 and KCNQ3 proteins play a major role in preventing excessive excitability of neurons in newborns, but other mechanisms that prevent constant neuron activity develop during infancy.
Mutations in the KCNQ2 gene are also involved in early-onset epileptic encephalopathy, a more severe condition than BFNS (described above) characterized by epilepsy and profound intellectual disability. The seizures begin in the first weeks of life and typically show little response to treatment. They usually go away in a few months to a few years but can return later in childhood. Most affected individuals are unable to talk, and they have low muscle tone (hypotonia) or very stiff muscles, causing difficulty with movement.
It has been suggested that KCNQ2 gene mutations that cause early-onset epileptic encephalopathy lead to production of an abnormal KCNQ2 protein that can still bind to normal subunits to form potassium channels. However, the presence of the abnormal KCNQ2 subunit keeps the channels from functioning, which likely leads to a severe reduction of the M-current. The resulting over-excitability of neurons can lead to seizures and brain dysfunction (encephalopathy).
Early-onset epileptic encephalopathy caused by KCNQ2 gene mutations resembles a condition called Ohtahara syndrome; however, seizures do not usually subside in people with Ohtahara syndrome. It is unclear whether the epileptic encephalopathy caused by KCNQ2 gene mutations is a form of Ohtahara syndrome or a separate disorder.
Cytogenetic Location: 20q13.3
Molecular Location on chromosome 20: base pairs 63,400,207 to 63,472,639
The KCNQ2 gene is located on the long (q) arm of chromosome 20 at position 13.3.
More precisely, the KCNQ2 gene is located from base pair 63,400,207 to base pair 63,472,639 on chromosome 20.
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 KCNQ2 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.
benign ; cell ; channel ; disability ; encephalopathy ; epilepsy ; epileptic ; familial ; gene ; hypotonia ; ions ; low muscle tone ; muscle tone ; mutation ; neonatal ; neuron ; potassium ; protein ; subunit ; syndrome ; voltage
You may find definitions for these and many other terms in the Genetics Home Reference 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.