Electrophysiological characterization of a large set of novel variants in the SCN5A-gene: identification of novel LQTS3 and BrS mutations

Abstract

SCN5A encodes for the α-subunit of the cardiac voltage-gated sodium channel Nav1.5. Gain-of-function mutations in SCN5A are related to congenital long QT syndrome (LQTS3) characterized by delayed cardiac repolarization, leading to a prolonged QT interval in the ECG. Loss-of-function mutations in SCN5A are related to Brugada syndrome (BrS), characterized by an ST-segment elevation in the right precordial leads (V1-V3). The aim of this study was the characterization of a large set of novel SCN5A variants found in patients with different cardiac phenotypes, mainly LQTS and BrS. SCN5A variants of 13 families were functionally characterized in Xenopus laevis oocytes using the two-electrode voltage-clamp technique. We found in most of the cases, but not all, that the electrophysiology of the variants correlated with the clinically diagnosed phenotype. A susceptibility to develop LQTS can be suggested in patients carrying the variants S216L, K480N, A572D, F816Y, and G983D. However, taking the phenotype into account, the presence of the variants in genomic data bases, the mutational segregation, combined with our in vitro and in silico experiments, the variants S216L, S262G, K480N, A572D, F816Y, G983D, and T1526P remain as variants of unknown significance. However, the SCN5A variants R568H and A993T can be classified as pathogenic LQTS3 causing mutations, while R222stop and R2012H are novel BrS causing mutations.

Mexiletine rescues a mixed biophysical phenotype of the cardiac sodium channel arising from the SCN5A mutation, N406K, found in LQT3 patients

“…These effects usually fall into two categories, gain or loss of channel function [4]. In “gain-of-function” mutations, an increase in the persistent late I Na during the action potential plateau, rather than in peak I Na is typically thought to be responsible for the type 3 long QT syndrome (LQT3) phenotype whereby repolarization is delayed and the QT interval is prolonged on the surface electrocardiogram (ECG) [5]. In contrast, “loss-of-function” mutations in SCN5A cause a decrease in peak I Na , leading to phenotypes including Brugada syndrome (BrS), cardiac conduction disturbance (CCD), congenital sick sinus syndrome (SSS), atrial standstill, AV block, sudden infant syndrome, and familial atrial fibrillation [3,6].…”

Sodium channel biophysics, late sodium current and genetic arrhythmic syndromes

“…In particular, Table 1 illustrates the above points in detail for long QT syndrome type 3 (LQTS3) using the relatively large number of examples from which selections can be made for analysis [33, 49, 55, 61, 65, 72, 85]. LQTS3 is one of a range of genetic (LQTS1–LQTS13) long QT syndromes characterised by prolonged QT intervals, reflecting increased ventricular APD and additional aberrant T -wave ECG signatures.…”

Alterations of Nedd4‐2‐binding capacity in PY‐motif of NaV1.5 channel underlie long QT syndrome and Brugada syndrome

“…SCN5A‐related variants leading to BrS originate through several mechanisms: non‐functional protein due to premature termination of the polypeptide chain, deficient trafficking of the functional channel protein into the plasma membrane, altered channel gating properties and decreased current ( I Na ) . On the other hand, gain‐of‐function SCN5A variants are related to LQT3 . Several mechanisms underlying gain‐of‐function SCN5A variants have been characterized, such as higher peak current density, shifts in the voltage‐dependence of activation or inactivation, increased speed of recovery from inactivation and an increase in the persistent or late inward sodium current .…”

“…On the other hand, gain‐of‐function SCN5A variants are related to LQT3 . Several mechanisms underlying gain‐of‐function SCN5A variants have been characterized, such as higher peak current density, shifts in the voltage‐dependence of activation or inactivation, increased speed of recovery from inactivation and an increase in the persistent or late inward sodium current . Although 293 distinct SCN5A variants have been discovered in patients with BrS and 110 in patients with LQT3, the molecular mechanisms of several variants are not well understood .…”