De Novo Mutation in the SCN5A Gene Associated with Brugada Syndrome

Abstract

Background: Brugada syndrome (BrS) is a genetically determined cardiac electrical disorder, characterized by typical electrocardiography (ECG) alterations, and it is an arrhythmogenic syndrome that may lead to sudden cardiac death. The most common genotype found among BrS patients is caused by mutations in the SCN5A gene, which lead to a loss of function of the cardiac sodium (Na⁺) channel (Na_v1.5) by different mechanisms. Methods: The assay of confocal laser microscopy and western blot were used to identify the expression and location of L812Q at the cell surface. Characterization of Nav1.5 L812Q mutant Na⁺ channels was text by patch-clamp recordings, and the PHYRE2 server was used to build a model for human Nav1.5 channel. Results: Here, we report that a novel missense SCN5A mutation, L812Q, localized in the DII-S4 transmembrane region of the Na_v1.5 channel protein, was identified in an index patient who showed a typical BrS type-1 ECG phenotype. The mutation was absent in the patient's parents and brother. Heterologous expression of the wild-type (WT) and L812Q mutant Na_v1.5 channels in human embryonic kidney cells (HEK293 cells) reveals that the mutation results in a reduction of Na⁺ current density as well as ∼20 mV hyperpolarizing shift of the voltage dependence of inactivation. The voltage dependence of activation and the time course for recovery from inactivation are not affected by the mutation. The hyperpolarizing shift of the voltage dependence of inactivation caused a reduction of the Na⁺ window current as well. In addition, western blot and confocal laser microscopy imaging experiments showed that the mutation causes fewer channel to be expressed at the membrane than WT channel. A large proportion of the mutant channels are retained in the cytoplasm, probably in the endoplasmic reticulum. Conclusion: The decrease of channel expression, hyperpolarizing shift of voltage dependence of inactivation, and a decline of Na⁺ window current caused by L812Q mutation lead to a reduction of Na⁺ current during the upstroke and the repolarization phases of cardiac action potential, which contribute to the development of BrS.

Uncoupling sodium channel dimers rescues phenotype of pain-linked Nav1.7 mutation

“…13 Dimerization affects severity of pain-linked mutation induced hNav1.7 gating changes 14 Inhibiting dimerization drastically reduced the persistent current of hNav1.7/A1632E ( Fig. 5 shown that the co-expression of a trafficking deficient mutation with WT reduced channel expression 27 on the cell membrane (Wang et al, 2015). There might be parallels between these findings and those 28 reported here on the hNav1.7/R896Q mutation.…”

Modeling the human Na_v1.5 sodium channel: structural and mechanistic insights of ion permeation and drug blockade

“…Perhaps, the most complete hNa v 1.5 model developed so far was the model reported by Wang et al 14 This model focused on a rare L812Q mutation located at the S4 helix of domain II. The models for the individual four transmembrane sub-domains were generated through the PHYRE2 15 server and assembled through a superposition on the NavAB bacterial ion channel using Chimera software.…”

Gene Polymorphisms Associated with Atrial Fibrillation

“…In a study conducted in the Chinese population, localized in the domain II S4 segment of NaV1.5 α subunit protein, a new mutation, L812Q mutation, has been described. In this study, it was shown that this mutation improved the sodium channel inactivation process and disrupted the membrane expression of the canal in BrS patients [18]. In a Dutch population study, it was determined that SCN5A gene mutations, which cause loss of function in BrS patients, are associated with dilation and deterioration in contractile function of both ventricles [20].…”

“…Depolarization or repolarization of cardiac action potential may be affected by due to reduced sodium current. Nevertheless, the underlying pathophysiological mechanism of the BrS phenotype is still being discussed [18]. BrS is defined as a disease characterized by sudden cardiac death characterized by a right bundle branch with an ST segment elevation in leads V1 and V2 in 1992.…”