Electrocardiographic Features in SCN5A Mutation-Positive Patients with Brugada and Early Repolarization Syndromes: A Systematic Review and Meta-Analysis

Background: Early repolarization syndrome (ERS) and Brugada syndrome (BrS) are both J-wave syndromes. Both can involve mutations in the SCN5A gene but may exhibit distinct electrocardiographic (ECG) differences. The aim of this systematic review and meta-analysis is to investigate possible differences in ECG markers between SCN5A positive patients with ERS and BrS. Methods: PubMed and Embase, were searched from their inception to October 20th, 2021 for human studies containing the search terms “SCN5A” and “variant” and “early reporlarization” or “Brugada”, with no language restrictions. Results: A total of 328 studies were identified. After full text screening, 12 studies met our inclusion criteria and were included in this present study. 104 ERS patients (mean age: 30.86 ±14.45) and 2000 BrS patients (mean age: 36.17 ±11.39) were studied. Our meta-analysis found that ERS patients had a significantly lower heart rate (standardized mean difference [SMD]a= 14.69, 95% confidence interval [CI] = 21.43, 7.94, P = 0.0001), shorter QRS duration (SMD = 13.90, 95% CI = 17.16, 10.65, P = 0.0001) and shorter QTc [corrected QT interval] (SDM = 21.52, 95% CI = 33.77, 9.26, P = 0.0006) than BrS patients. Conclusion: BrS patients with positive SCN5A mutations exhibited prolonged QRS, indicating conduction abnormalities, whereas ERS patients with positive SCN5A mutations showed normal QRS. By contrast, whilst QTc intervals were longer in BrS than in ERS SCN5A positive patients, they were within normal limits. Further studies are needed to examine the implications of these findings for arrhythmic risk stratification.

Zfhx3 Transcription Factor Represses the Expression of SCN5A Gene and Decreases Sodium Current Density (INa)

The ZFHX3 and SCN5A genes encode the zinc finger homeobox 3 (Zfhx3) transcription factor (TF) and the human cardiac Na+ channel (Nav1.5), respectively. The effects of Zfhx3 on the expression of the Nav1.5 channel, and in cardiac excitability, are currently unknown. Additionally, we identified three Zfhx3 variants in probands diagnosed with familial atrial fibrillation (p.M1260T) and Brugada Syndrome (p.V949I and p.Q2564R). Here, we analyzed the effects of native (WT) and mutated Zfhx3 on Na+ current (INa) recorded in HL-1 cardiomyocytes. ZFHX3 mRNA can be detected in human atrial and ventricular samples. In HL-1 cardiomyocytes, transfection of Zfhx3 strongly reduced peak INa density, while the silencing of endogenous expression augmented it (from −65.9 ± 8.9 to −104.6 ± 10.8 pA/pF; n ≥ 8, p < 0.05). Zfhx3 significantly reduced the transcriptional activity of human SCN5A, PITX2, TBX5, and NKX25 minimal promoters. Consequently, the mRNA and/or protein expression levels of Nav1.5 and Tbx5 were diminished (n ≥ 6, p < 0.05). Zfhx3 also increased the expression of Nedd4-2 ubiquitin-protein ligase, enhancing Nav1.5 proteasomal degradation. p.V949I, p.M1260T, and p.Q2564R Zfhx3 produced similar effects on INa density and time- and voltage-dependent properties in WT. WT Zfhx3 inhibits INa as a result of a direct repressor effect on the SCN5A promoter, the modulation of Tbx5 increasing on the INa, and the increased expression of Nedd4-2. We propose that this TF participates in the control of cardiac excitability in human adult cardiac tissue.

Peripartum Management of Patient with Long QT3 after Successful ICD Device Discharge Resulting in Device Failure: A Case Report

Background Long QT3 syndrome (LQT3) is a gain of function mutation of the SCN5A gene that is inherited in an autosomal dominant fashion. LQT3 results in an increase in arrhythmic events during rest, sleep, and bradycardia by extending the QT interval and inducing Torsades de pointes and sudden cardiac death. Attempting to block the sodium channel with Class I anti-arrhythmics or blocking adrenergic tone with beta blockers especially in women, have shown to be beneficial. There have been few large-scale studies on treating patients with LQT3 due to its lethality and underreported number of cases. Specifically, the safety and efficacy of pharmacologic treatment in pregnant LQT3 patients is unknown. Case summary This case demonstrates the safe use of Mexiletine and Propranolol in a third trimester pregnant LQT3 patient after a presumed ventricular arrhythmia and device-lead electrical short from therapy rendered her Implantable Cardioverter Defibrillator (ICD) inoperable in a VVI mode. With appropriate medications, the patient was safely monitored through the remainder of her pregnancy and safely delivered at 36 weeks of pregnancy a healthy baby girl. The daughter, heterozygous for LQT3, showed no evidence of intrauterine growth restriction or other side effects from the medications. Discussion There are many variants of the SCN5A gene mutations that can lead to different phenotypes and not all mutations are responsive to the same medications. In this case, Mexiletine and Propranolol, both of which have only recently shown to benefit certain variants or LQT3 respectively, were safely started during the third trimester of pregnancy without harming the fetus.

Association of SCN5A gene polymorphism with dilated cardiomyopathy

Subjects and methods. The study included patients with IDC (group 1; n=111, 89.2% men, average age 51.7±9.7 years) and ICM (group 2; n=110, 91.5% men, average age 58.7±8.4 years). All patients (IDC and ICM) underwent coronary angiography. Based on the anamnesis data and instrumental studies, those patients who could be said to have no risk factors for the development of dilatation of the heart cavities were identified in the group 1. And those patients who were reliably diagnosed with coronary artery disease were in the group 2, that is, dilatation of the heart cavities is due to a previous myocardial infarction, existing angina pectoris. The control group (n=121, average age 53.6±4.8 years) included patients who had no manifestations of cardiovascular diseases. The patients underwent laboratory and instrumental studies, as well as molecular and genetic studies of the A/G polymorphism of the SCN5A gene (rs1805124).Results. In the group with IDC 51.4% of patients were carriers of the common homozygous AA genotype, the heterozygous AG genotype-40.5%, and the rare homozygous GG genotype-8.1%. In the control group 63.3% of patients were identified as carriers of a homozygous genotype by a common allele, and 33.5% were carriers heterozygous genotype, and homozygous genotype for a rare allele – 3.2%. The analysis revealed a statistically significant decrease in the frequency of carrying the homozygous AA genotype in patients with IDC compared to the control group of the rs1805124 polymorphism of the SCN5A gene. In the group of patients with ICM, the А allele (69.5% vs. 80.1%, p=0.003) and the AA genotype (50.9% vs. 63.3%, p=0.030) were significantly less common than in the control group. The rare homozygous GG genotype was statically more common in patients with ICM compared to the control group (11.8% vs. 3.2%, p=0.004). Also, the G allele in the group of patients with ICM was detected statically significantly more often than in the control group (30.5% vs. 19.9%, p= 0.003).Conclusion. The polymorphic locus rs1805124 of the SCN5A gene is associated with both IDC and ICM. Homozygous genotype AA and allele A are conditionally protective factors for the development of these conditions in men.

Genetic Characteristics and Transcriptional Regulation of Sodium Channel Related Genes in Chinese Patients With Brugada Syndrome

Objective: To investigate the genetic characteristics and transcriptional regulation of the SCN5A gene of Brugada syndrome (BrS) patients in China.Methods: Using PubMed, Medline, China National Knowledge Internet (CNKI), and Wanfang Database, Chinese patients with BrS who underwent SCN5A gene testing were studied.Results: A total of 27 suitable studies involving Chinese BrS patients who underwent the SCN5A gene test were included. A total of 55 SCN5A gene mutations/variations were reported in Chinese BrS patients, including 10 from southern China and 45 from northern China. Mutations/variations of BrS patients from southern China mostly occurred in the regions of the α-subunit of Nav1.5, including DIII (Domain III), DIV, DIII-DIV, C-terminus regions, and the 3'UTR region. Furthermore, we analyzed the post-transcriptional modifications (PTMs) throughout the Nav1.5 protein encoded by SCN5A and found that the PTM changes happened in 72.7% of BrS patients from southern China and 26.7% from northern China.Conclusions: SCN5A mutations/variations of BrS patients in southern China mostly occurred in the DIII-DIV to C-terminus region and the 3'-UTR region of the SCN5A gene, different from northern China. PTM changes were consistent with the mutation/variation distribution of SCN5A, which might be involved in the regulation of the pathogenesis of BrS patients.

Brugada syndrome with a novel missense mutation D252N in SCN5A gene: a case report

Brugada syndrome is an inherited cardiac arrhythmia that follows autosomal dominant transmission and can cause sudden death. This paper reported a case of Brugada syndrome in a 43-year-old male patient with no clinical symptoms. Brugada-type 2-ECG changes were accidentally detected. Flecainide test was done and proved positive. Gene analysis revealed a novel missense mutation in the SCN5A gene with a genetic variation of D252N. This novel mutation has not been reported on any genetic databases related to Brugada syndrome. Functional protein analysis software suggested that the mutation occurs in the highly conserved gene and probably has a damaging effect. This is the first Brugada syndrome case reported with a mutation in the SCN5A gene in Vietnam.

The SCN5A point mutation M1875T, associated with familial atrial fibrillation, causes a gain-of-function effect of the cardiac Nav1.5 channel in atrial cardiomyocytes

Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): British Heart Foundation Leducq Foundation Background The point mutation M1875T in the SCN5A gene, which encodes the pore-forming α-subunit of the cardiac voltage-gated Na+ channel Nav1.5, has been associated with familial atrial fibrillation (AF), but its effects on atrial cardiomyocyte electrophysiology is unclear. Aim To investigate the effect of the point mutation M1875T on atrial electrophysiological parameters. Methods In a novel heterozygous knock-in murine model (Scn5a-M1875T+/-), whole-cell patch clamp electrophysiology was used to investigate Na+ currents in left atrial (LA) cardiomyocytes isolated from hearts of young adult mice (10-16 weeks). LA microelectrode and optical mapping recordings were used to study action potential (AP) characteristics. Cardiac size and function were measured by transthoracic echocardiography. Atrial Scn5a gene and Nav1.5 protein expression were assessed by Rt-PCR and Western blot. Results The Na+ current was increased in cardiomyocytes isolated from Scn5a-M1875T+/- LA (wildtype (WT) -22.7 ± 0.9 pA/pF (N = 14, n = 115); Scn5a-M1875T+/- -28.3 ± 1.1 pA/pF (N = 15, n = 117)). Scn5a-M1875T+/- intact isolated superfused LA had an elevated AP amplitude (100 ms pacing cycle length (PCL): WT 86.4 ± 0.9 mV (N = 8, n = 24); Scn5a-M1875T+/- 91.2 ± 0.7 mV (N = 8, n = 25)) and a faster peak upstroke velocity (100 ms PCL: WT 127.98 ± 3.28 mV/ms; Scn5a-M1875T+/- 142.80 ± 3.98 mV/ms). AP duration (APD) was not different apart from a small APD shortening at slow rates. Echocardiography revealed no difference in size and function at the age of investigation. Atrial Scn5a gene and Nav1.5 protein expression were comparable. When challenged with flecainide (1 µM), Scn5a-M1875T+/- LA showed less conduction slowing than WT (100 ms PCL: WT -10.43 ± 1.27 cm/s (N = 12); Scn5a-M1875T+/- -6.10 ± 1.34 cm/s (N = 12)). 5 µM flecainide caused significant increase in WT refractoriness (7/12 atria lost 1:1 capture at PCL ≤ 120 ms) compared to Scn5a-M1875T+/- (1/12). Conclusion(s): SCN5A point mutation M1875T increases the Na+ current in atrial cardiomyocytes and intact atria, leading to a faster AP upstroke and an attenuated response to flecainide. Abstract Figure 1: Current-Voltage relationship

Novel SCN5A p.Val1667Asp Missense Variant Segregation and Characterization in a Family with Severe Brugada Syndrome and Multiple Sudden Deaths

Genetic testing in Brugada syndrome (BrS) is still not considered to be useful for clinical management of patients in the majority of cases, due to the current lack of understanding about the effect of specific variants. Additionally, family history of sudden death is generally not considered useful for arrhythmic risk stratification. We sought to demonstrate the usefulness of genetic testing and family history in diagnosis and risk stratification. The family history was collected for a proband who presented with a personal history of aborted cardiac arrest and in whom a novel variant in the SCN5A gene was found. Living family members underwent ajmaline testing, electrophysiological study, and genetic testing to determine genotype-phenotype segregation, if any. Patch-clamp experiments on transfected human embryonic kidney 293 cells enabled the functional characterization of the SCN5A novel variant in vitro. In this study, we provide crucial human data on the novel heterozygous variant NM_198056.2:c.5000T>A (p.Val1667Asp) in the SCN5A gene, and demonstrate its segregation with a severe form of BrS and multiple sudden deaths. Functional data revealed a loss of function of the protein affected by the variant. These results provide the first disease association with this variant and demonstrate the usefulness of genetic testing for diagnosis and risk stratification in certain patients. This study also demonstrates the usefulness of collecting the family history, which can assist in understanding the severity of the disease in certain situations and confirm the importance of the functional studies to distinguish between pathogenic mutations and harmless genetic variants.