KCNQ2 Gene

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This entry is adapted from the peer-reviewed paper https://medlineplus.gov/genetics/gene/kcnq2

Potassium voltage-gated channel subfamily Q member 2

genes

1. Introduction

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.

2. Health Conditions Related to Genetic Changes

2.1. 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.

2.2. Other Disorders

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.

3. Other Names for This Gene

BFNC
BFNS1
EBN
EBN1
EIEE7
ENB1
HNSPC
KCNA11
KCNQ2_HUMAN
KQT-like 2
KV7.2
KVEBN1
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

References

Biervert C, Schroeder BC, Kubisch C, Berkovic SF, Propping P, Jentsch TJ,Steinlein OK. A potassium channel mutation in neonatal human epilepsy. Science.1998 Jan 16;279(5349):403-6.
Castaldo P, del Giudice EM, Coppola G, Pascotto A, Annunziato L, Taglialatela M. Benign familial neonatal convulsions caused by altered gating of KCNQ2/KCNQ3potassium channels. J Neurosci. 2002 Jan 15;22(2):RC199.
Chung HJ, Jan YN, Jan LY. Polarized axonal surface expression of neuronal KCNQchannels is mediated by multiple signals in the KCNQ2 and KCNQ3 C-terminaldomains. Proc Natl Acad Sci U S A. 2006 Jun 6;103(23):8870-5.
Lerche H, Biervert C, Alekov AK, Schleithoff L, Lindner M, Klinger W,Bretschneider F, Mitrovic N, Jurkat-Rott K, Bode H, Lehmann-Horn F, Steinlein OK.A reduced K+ current due to a novel mutation in KCNQ2 causes neonatalconvulsions. Ann Neurol. 1999 Sep;46(3):305-12.
Millichap JJ, Cooper EC. KCNQ2 Potassium Channel Epileptic EncephalopathySyndrome: Divorce of an Electro-Mechanical Couple? Epilepsy Curr. 2012Jul;12(4):150-2. doi: 10.5698/1535-7511-12.4.150.
Rogawski MA. KCNQ2/KCNQ3 K+ channels and the molecular pathogenesis ofepilepsy: implications for therapy. Trends Neurosci. 2000 Sep;23(9):393-8.Review.
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 KCNQ2mutations in Ohtahara syndrome. Ann Neurol. 2012 Aug;72(2):298-300. doi:10.1002/ana.23620.
Schroeder BC, Kubisch C, Stein V, Jentsch TJ. Moderate loss of function ofcyclic-AMP-modulated KCNQ2/KCNQ3 K+ channels causes epilepsy. Nature. 1998 Dec17;396(6712):687-90.
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 thefunctional and mutation spectrum. Brain. 2003 Dec;126(Pt 12):2726-37.
Soldovieri MV, Miceli F, Bellini G, Coppola G, Pascotto A, Taglialatela M.Correlating the clinical and genetic features of benign familial neonatalseizures (BFNS) with the functional consequences of underlying mutations.Channels (Austin). 2007 Jul-Aug;1(4):228-33.
Volkers L, Rook MB, Das JH, Verbeek NE, Groenewegen WA, van Kempen MJ,Lindhout D, Koeleman BP. Functional analysis of novel KCNQ2 mutations found inpatients with Benign Familial Neonatal Convulsions. Neurosci Lett. 2009 Oct2;462(1):24-9. doi: 10.1016/j.neulet.2009.06.064.
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 theM-channel. Science. 1998 Dec 4;282(5395):1890-3.
Weckhuysen S, Mandelstam S, Suls A, Audenaert D, Deconinck T, Claes LR, DeprezL, Smets K, Hristova D, Yordanova I, Jordanova A, Ceulemans B, Jansen A, HasaertsD, 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.

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Subjects: Genetics & Heredity

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Dean Liu

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Entry Collection: MedlinePlus

Update Date: 23 Dec 2020

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