Benign Familial Neonatal Seizures

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This entry is adapted from the peer-reviewed paper https://medlineplus.gov/genetics/condition/benign-familial-neonatal-seizures

Benign familial neonatal seizures (BFNS) is a condition characterized by recurrent seizures in newborn babies. The seizures begin around day 3 of life and usually go away within 1 to 4 months. The seizures can involve only one side of the brain (focal seizures) or both sides (generalized seizures). Many infants with this condition have generalized tonic-clonic seizures (also known as grand mal seizures). This type of seizure involves both sides of the brain and affects the entire body, causing muscle rigidity, convulsions, and loss of consciousness.

genetic conditions

1. Introduction

A test called an electroencephalogram (EEG) is used to measure the electrical activity of the brain. Abnormalities on an EEG test, measured during no seizure activity, can indicate a risk for seizures. However, infants with BFNS usually have normal EEG readings. In some affected individuals, the EEG shows a specific abnormality called the theta pointu alternant pattern. By age 2, most affected individuals who had EEG abnormalities have a normal EEG reading.

Typically, seizures are the only symptom of BFNS, and most people with this condition develop normally. However, some affected individuals develop intellectual disability that becomes noticeable in early childhood. A small percentage of people with BFNS also have a condition called myokymia, which is an involuntary rippling movement of the muscles. In addition, in about 15 percent of people with BFNS, recurrent seizures (epilepsy) will come back later in life after the seizures associated with BFNS have gone away. The age that epilepsy begins is variable.

2. Frequency

Benign familial neonatal seizures occurs in approximately 1 in 100,000 newborns.

3. Causes

Mutations in two genes, KCNQ2 and KCNQ3, have been found to cause BFNS. Mutations in the KCNQ2 gene are a much more common cause of the condition than mutations in the KCNQ3 gene.

The KCNQ2 and KCNQ3 genes provide instructions for making proteins that interact to form potassium channels. Potassium 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.

Channels made with the KCNQ2 and KCNQ3 proteins 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.

Mutations in the KCNQ2 or KCNQ3 gene result in a reduced or altered M-current, which leads to excessive excitability of neurons. 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 develop during infancy.

About 70 percent of people with BFNS have a mutation in either the KCNQ2 or the KCNQ3 gene. Researchers are working to identify other gene mutations involved in this condition.

4. Inheritance

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person inherits the mutation from one affected parent. A few cases result from new mutations in the KCNQ2 gene. These cases occur in people with no history of benign familial neonatal seizures in their family.

5. Other Names for This Condition

benign familial neonatal convulsions
benign familial neonatal epilepsy
benign neonatal convulsions
benign neonatal epilepsy
BFNS

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.
Miceli F, Soldovieri MV, Joshi N, Weckhuysen S, Cooper E, Taglialatela M.KCNQ2-Related Disorders. 2010 Apr 27 [updated 2018 Sep 27]. In: Adam MP, ArdingerHH, Pagon RA, Wallace SE, Bean LJH, Stephens K, Amemiya A, editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2020. Availablefrom http://www.ncbi.nlm.nih.gov/books/NBK32534/
Rogawski MA. KCNQ2/KCNQ3 K+ channels and the molecular pathogenesis ofepilepsy: implications for therapy. Trends Neurosci. 2000 Sep;23(9):393-8.Review.
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.

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Subjects: Genetics & Heredity

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Catherine Yang

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Update Date: 24 Dec 2020

Table of Contents

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1. Introduction

2. Frequency

3. Causes

4. Inheritance

5. Other Names for This Condition

References

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1. Introduction

2. Frequency

3. Causes

3.1. The Genes Associated with Benign Familial Neonatal Seizures

4. Inheritance

5. Other Names for This Condition

References