Dataset Information

A heterozygous deletion mutation in the cardiac sodium channel gene SCN5A with loss- and gain-of-function characteristics manifests as isolated conduction disease, without signs of Brugada or long QT syndrome.

ABSTRACT:

Background

The SCN5A gene encodes for the ?-subunit of the cardiac sodium channel NaV1.5, which is responsible for the rapid upstroke of the cardiac action potential. Mutations in this gene may lead to multiple life-threatening disorders of cardiac rhythm or are linked to structural cardiac defects. Here, we characterized a large family with a mutation in SCN5A presenting with an atrioventricular conduction disease and absence of Brugada syndrome.

Method and results

In a large family with a high incidence of sudden cardiac deaths, a heterozygous SCN5A mutation (p.1493delK) with an autosomal dominant inheritance has been identified. Mutation carriers were devoid of any cardiac structural changes. Typical ECG findings were an increased P-wave duration, an AV-block I° and a prolonged QRS duration with an intraventricular conduction delay and no signs for Brugada syndrome. HEK293 cells transfected with 1493delK showed strongly (5-fold) reduced Na(+) currents with altered inactivation kinetics compared to wild-type channels. Immunocytochemical staining demonstrated strongly decreased expression of SCN5A 1493delK in the sarcolemma consistent with an intracellular trafficking defect and thereby a loss-of-function. In addition, SCN5A 1493delK channels that reached cell membrane showed gain-of-function aspects (slowing of the fast inactivation, reduction in the relative fraction of channels that fast inactivate, hastening of the recovery from inactivation).

Conclusion

In a large family, congregation of a heterozygous SCN5A gene mutation (p.1493delK) predisposes for conduction slowing without evidence for Brugada syndrome due to a predominantly trafficking defect that reduces Na(+) current and depolarization force.

SUBMITTER: Zumhagen S

PROVIDER: S-EPMC3695936 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Publications

A heterozygous deletion mutation in the cardiac sodium channel gene SCN5A with loss- and gain-of-function characteristics manifests as isolated conduction disease, without signs of Brugada or long QT syndrome.

Zumhagen Sven S Veldkamp Marieke W MW Stallmeyer Birgit B Baartscheer Antonius A Eckardt Lars L Paul Matthias M Remme Carol Ann CA Bhuiyan Zahurul A ZA Bezzina Connie R CR Schulze-Bahr Eric E

PloS one 20130628 6

<h4>Background</h4>The SCN5A gene encodes for the α-subunit of the cardiac sodium channel NaV1.5, which is responsible for the rapid upstroke of the cardiac action potential. Mutations in this gene may lead to multiple life-threatening disorders of cardiac rhythm or are linked to structural cardiac defects. Here, we characterized a large family with a mutation in SCN5A presenting with an atrioventricular conduction disease and absence of Brugada syndrome.<h4>Method and results</h4>In a large fam ...[more]

PMID: 23840796

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Project description:Genome-wide association studies (GWAS) have suggested that sequence variation in cis-regulatory elements (CREs) modulate common disease risk and trait variation. However, identification of the majority of these causal variants and their mechanism of action have remained significant challenges. We used reporter assays for all common variants at the QT interval associated SCN5A GWAS locus with the goal of identifying causal variants for the association. A target region of ~500kb containing SCN5A was defined based on recombination hotspots (rate>10cM/Mb; estimated from HapMap) flanking the 5 independent QT interval GWAS hits. Within this region, all common variants (minor allele frequency >5%), from the 1000 Genomes European ancestry populations, in moderate linkage disequilibrium (LD; r2>0.3) with any of the 5 sentinel hits, were selected for analyses. Of a total 121 variants selected, 112 variants in 104 amplicons passed primer design (amplicon size 256-617bp; median 397bp), with both alleles of 106 variants successfully cloned along with flanking sequences into 98 amplicons upstream of a minimal promoter-driven firefly luciferase gene in pGL4.23. Cardiomyocyte cells, AC16 (human) and HL1 (mouse), were transfected with test constructs and Renilla luciferase vector (for transfection normalization) in triplicate; luciferase assays were performed 24h later. All cloning and reporter assays were performed in 96- and 24-well plates. In reporter assays across the two cell lines, compared to empty vector, 37 amplicons showed enhancer activity (z-score>99 %tile), with a concordance rate of ~70%. Of these 37 enhancer CREs, 9 overlapped open chromatin regions (DNase-seq peaks) observed in adult human heart tissue, largest among all human tissues evaluated by the RoadMap Epigenomics project. Of these 37 enhancer CREs, 12 showed allelic difference in reporter activity (P<0.05), thus identifying at least one enhancer CRE variant in high-to-moderate LD with each of the 5 sentinel hits. Using GTEx heart left ventricle (n=190) gene expression data, we showed correlation between SCN5A expression and the number of QT interval prolonging alleles across the 5 index SNPs. We are currently assessing the binding of cardiac nuclear factors at the 12 enhancer CRE variants by gel-shift assays and the effect of CRISPR-Cas9 mediated CRE deletion on SCN5A expression in AC16 and HL1 cells, an analyses helped by evaluation of AC16 and HL1 cells by RNA-seq, ATAC-seq and karyotyping. Thus, independent of the publicly available epigenomic data, which are of limited cell-type relevance, an unbiased in vitro reporter screen for CREs overlapping all common variants associated with QT interval at the SCN5A GWAS locus identified 12 common cis-regulatory variants that map to cardiac open chromatin regions and correlate with SCN5A cardiac expression.

Dataset Information

A heterozygous deletion mutation in the cardiac sodium channel gene SCN5A with loss- and gain-of-function characteristics manifests as isolated conduction disease, without signs of Brugada or long QT syndrome.

Background

Method and results

Conclusion

Publications

A heterozygous deletion mutation in the cardiac sodium channel gene SCN5A with loss- and gain-of-function characteristics manifests as isolated conduction disease, without signs of Brugada or long QT syndrome.

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