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.
Health Conditions Related to Genetic Changes
Benign familial neonatal seizures
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.More About This Health Condition
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.
Other Names for This Gene
- KQT-like 2
- potassium channel, voltage gated KQT-like subfamily Q, member 2
- potassium voltage-gated channel subfamily KQT member 2
- potassium voltage-gated channel, KQT-like subfamily, member 2
- voltage-gated potassium channel subunit Kv7.2
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
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- Castaldo P, del Giudice EM, Coppola G, Pascotto A, Annunziato L, Taglialatela M. Benign familial neonatal convulsions caused by altered gating of KCNQ2/KCNQ3 potassium channels. J Neurosci. 2002 Jan 15;22(2):RC199. doi: 10.1523/JNEUROSCI.22-02-j0003.2002. Citation on PubMed
- Chung HJ, Jan YN, Jan LY. Polarized axonal surface expression of neuronal KCNQ channels is mediated by multiple signals in the KCNQ2 and KCNQ3 C-terminal domains. Proc Natl Acad Sci U S A. 2006 Jun 6;103(23):8870-5. doi: 10.1073/pnas.0603376103. Epub 2006 May 30. Citation on PubMed or Free article on PubMed Central
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- Rogawski MA. KCNQ2/KCNQ3 K+ channels and the molecular pathogenesis of epilepsy: implications for therapy. Trends Neurosci. 2000 Sep;23(9):393-8. doi: 10.1016/s0166-2236(00)01629-5. Citation on PubMed
- Saitsu H, Kato M, Koide A, Goto T, Fujita T, Nishiyama K, Tsurusaki Y, Doi H, Miyake N, Hayasaka K, Matsumoto N. Whole exome sequencing identifies KCNQ2 mutations in Ohtahara syndrome. Ann Neurol. 2012 Aug;72(2):298-300. doi: 10.1002/ana.23620. No abstract available. Citation on PubMed
- Schroeder BC, Kubisch C, Stein V, Jentsch TJ. Moderate loss of function of cyclic-AMP-modulated KCNQ2/KCNQ3 K+ channels causes epilepsy. Nature. 1998 Dec 17;396(6712):687-90. doi: 10.1038/25367. Citation on PubMed
- Singh NA, Westenskow P, Charlier C, Pappas C, Leslie J, Dillon J, Anderson VE, Sanguinetti MC, Leppert MF; BFNC Physician Consortium. KCNQ2 and KCNQ3 potassium channel genes in benign familial neonatal convulsions: expansion of the functional and mutation spectrum. Brain. 2003 Dec;126(Pt 12):2726-37. doi: 10.1093/brain/awg286. Epub 2003 Oct 8. Citation on PubMed
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- Volkers L, Rook MB, Das JH, Verbeek NE, Groenewegen WA, van Kempen MJ, Lindhout D, Koeleman BP. Functional analysis of novel KCNQ2 mutations found in patients with Benign Familial Neonatal Convulsions. Neurosci Lett. 2009 Oct 2;462(1):24-9. doi: 10.1016/j.neulet.2009.06.064. Epub 2009 Jun 25. Citation on PubMed
- Wang HS, Pan Z, Shi W, Brown BS, Wymore RS, Cohen IS, Dixon JE, McKinnon D. KCNQ2 and KCNQ3 potassium channel subunits: molecular correlates of the M-channel. Science. 1998 Dec 4;282(5395):1890-3. doi: 10.1126/science.282.5395.1890. Citation on PubMed
- Weckhuysen S, Mandelstam S, Suls A, Audenaert D, Deconinck T, Claes LR, Deprez L, Smets K, Hristova D, Yordanova I, Jordanova A, Ceulemans B, Jansen A, Hasaerts D, Roelens F, Lagae L, Yendle S, Stanley T, Heron SE, Mulley JC, Berkovic SF, Scheffer IE, de Jonghe P. KCNQ2 encephalopathy: emerging phenotype of a neonatal epileptic encephalopathy. Ann Neurol. 2012 Jan;71(1):15-25. doi: 10.1002/ana.22644. Citation on PubMed