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Mutation screening of SCN2A in schizophrenia and identification of a novel loss-of-function mutation.

ABSTRACT: OBJECTIVES:There is a growing body of evidence suggesting a shared genetic susceptibility between many neuropsychiatric disorders, including schizophrenia, autism, intellectual disability (ID) and epilepsy. The sodium channel, voltage-gated type II ? subunit gene SCN2A has been shown to exhibit loss-of-function (LoF) mutations in individuals with seizure disorders, ID, autism and schizophrenia. The role of LoF mutations in schizophrenia is still uncertain with only one such mutation identified to date. METHODS:To seek additional evidence for a role for LoF mutations at SCN2A in schizophrenia we performed mutation screening of the entire coding sequence in 980 schizophrenia cases. Given an absence of LoF mutations in a public exome cohort (ESP6500, N=6503), we did not additionally sequence controls. RESULTS:We identified a novel, nonsense (i.e. stop codon) mutation in one case (E169X) that is absent in 4300 European-American and 2203 African-American individuals from the NHLBI Exome Sequencing Project. This is the second LoF allele identified in a schizophrenia case to date. We also show a novel, missense variant, V1282F, that occurs in two cases and is absent in the control dataset. CONCLUSION:We argue that very rare, LoF mutations at SCN2A act in a moderately penetrant manner to increase the risk of developing several neuropsychiatric disorders including seizure disorders, ID, autism and schizophrenia.

SUBMITTER: Carroll LS

PROVIDER: S-EPMC4756433 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Mutation screening of SCN2A in schizophrenia and identification of a novel loss-of-function mutation.

Carroll Liam S LS Woolf Rebecca R Ibrahim Yousef Y Williams Hywel J HJ Dwyer Sarah S Walters James J Kirov George G O'Donovan Michael C MC Owen Michael J MJ

Psychiatric genetics 20160401 2

<h4>Objectives</h4>There is a growing body of evidence suggesting a shared genetic susceptibility between many neuropsychiatric disorders, including schizophrenia, autism, intellectual disability (ID) and epilepsy. The sodium channel, voltage-gated type II α subunit gene SCN2A has been shown to exhibit loss-of-function (LoF) mutations in individuals with seizure disorders, ID, autism and schizophrenia. The role of LoF mutations in schizophrenia is still uncertain with only one such mutation iden ...[more]

PMID: 26555645

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Project description:Mutations in genes coding for subunits of the neuronal nicotinic acetylcholine receptor (nAChR) have been involved in familial sleep-related hypermotor epilepsy (also named autosomal dominant nocturnal frontal lobe epilepsy, ADNFLE). Most of these mutations reside in CHRNA4 and CHRNB2 genes, coding for the ?4 and ?2 nAChR subunits, respectively. Two mutations with contrasting functional effects were also identified in the CHRNA2 gene coding for the ?2 subunit. Here, we report the third mutation in the CHRNA2, found in a patient showing ADNFLE. The patient was examined by scalp EEG, contrast-enhanced brain magnetic resonance imaging (MRI), and nocturnal video-polysomnographic recording. All exons and the exon-intron boundaries of CHRNA2, CHRNA4, CHRNB2, CRH, KCNT1 were amplified and Sanger sequenced. In the proband, we found a c.754T>C (p.Tyr252His) missense mutation located in the N-terminal ligand-binding domain and inherited from the mother. Functional studies were performed by transient co-expression of ?2 and ?2 Tyr252His , with either ?2 or ?4, in human embryonic kidney (HEK293) cells. Equimolar amounts of subunits expression were obtained by using F2A-based multi-cistronic constructs encoding for the genes relative to the nAChR subunits of interest and for the enhanced green fluorescent protein. The mutation reduced the maximal currents by approximately 80% in response to saturating concentrations of nicotine in homo- and heterozygous form, in both the ?2?4 and ?2?2 nAChR subtypes. The effect was accompanied by a strong right-shift of the concentration-response to nicotine. Similar effects were observed using ACh. Negligible effects were produced by ?2Tyr252His on the current reversal potential. Moreover, binding of (±)-[3H]Epibatidine revealed an approximately 10-fold decrease of both Kd and Bmax (bound ligand in saturating conditions), in cells expressing ?2Tyr252His. The reduced Bmax and whole-cell currents were not caused by a decrease in mutant receptor expression, as minor effects were produced by ?2Tyr252His on the level of transcripts and the membrane expression of ?2?4 nAChR. Overall, these results suggest that ?2Tyr252His strongly reduced the number of channels bound to the agonist, without significantly altering the overall channel expression. We conclude that mutations in CHRNA2 are more commonly linked to ADNFLE than previously thought, and may cause a loss-of-function phenotype.

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Mutation screening of SCN2A in schizophrenia and identification of a novel loss-of-function mutation.

Publications

Mutation screening of SCN2A in schizophrenia and identification of a novel loss-of-function mutation.

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