A Common Polymorphism of the Human Cardiac Sodium Channel Alpha Subunit (SCN5A) Gene Is Associated with Sudden Cardiac Death in Chronic Ischemic Heart Disease

Polymorphic Variants of SCN5A Gene (rs41312433 and rs1805124) Associated with Coronary Artery Affliction in Patients with Severe Arrhythmias

Several mutations in this gene for the α subunit of the cardiac sodium channel have been identified in a heterogeneous subset of cardiac rhythm syndromes, including Brugada syndrome, progressive cardiac conduction defect, sick sinus node syndrome, atrial fibrillation and dilated cardiomyopathy. The aim of our study was to associate some SCN5A polymorphic variants directly with confirmed coronary stenoses in patients with non-LQTS ventricular fibrillation/flutter treated by an implantable cardioverter defibrillator.

MATERIALS AND METHODS

A group of 32 unrelated individuals, aged 63 ± 12 years, was included in the study. All the patients were examined, diagnosed and treated with an implantable cardioverter defibrillator at the Department of Internal Cardiology Medicine, Faculty Hospital Brno. The control group included 87 persons of similar age without afflicted coronary circulation, which was confirmed coronagraphically. Genomic DNA was extracted from samples of peripheral blood according to the standard protocol. Two SCN5A polymorphisms-IVS9-3C/A (rs41312433) and A1673G (rs1805124, H558R)-were examined in association with coronary artery stenosis in the patients.

RESULTS

In the case-control study, no significant differences in genotype distribution/allelic frequencies were observed for IVS9-3c>a and A1673G gene polymorphisms between patients with severe arrhythmias and healthy persons. The distribution of SCN5A double genotypes was not significantly different among different types of arrhythmias according to their ejection fraction in arrhythmic patients (p = 0.396). The ventricular arrhythmias with an ejection fraction below 40% were found to be 10.67 times more frequent in patients with multiple coronary stenosis with clinically valid sensitivity, specificity and power tests. In the genotype-phenotype study, we observed a significant association of both SCN5A polymorphisms with the stenosis of coronary vessels in the patients with severe arrhythmia. The double genotype of polymorphisms IVS9-3C/A together with A1673G (CCAA) as well as their simple genotypes were associated with significant multiple stenosis of coronary arteries (MVS) with high sensitivity and specificity (p = 0.05; OR = 5 (95% CI 0.99-23.34); sensitivity 0.70; specificity 0.682; power test 0.359) Moreover, when a concrete stenotic coronary artery was associated with SCN5A genotypes, the CCAA double genotype was observed to be five times more frequent in patients with significant stenosis in the right coronary artery (RCA) compared to those without affliction of this coronary artery (p = 0.05; OR = 5 (95% CI 0.99-23.34); sensitivity 0.682; specificity 0.700; power test 0.359). The CCAA genotype was also more frequent in patients without RCA affliction with MVS (p = 0.008); in patients with ACD affliction but without MVS (p = 0.008); and in patients with both ACD affliction and MVS compared to those without ACD affliction and MVS (p = 0.005).

CONCLUSIONS

Our study presents a highly sensitive and specific association of two polymorphisms in SCN5A with significant coronary artery stenoses in patients with potentially fatal ventricular arrhythmias. At the same time, these polymorphisms were not associated with arrhythmias themselves. Thus, SCN5A gene polymorphic variants may form a part of germ cell gene predisposition to ischemia.

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.

Type 2 Diabetes and Causes of Sudden Cardiac Death: A Systematic Review

Type 2 diabetes mellitus has been on the rise in recent years. A major cause of death in the United States is myocardial infarction with underlying coronary artery disease. Impairment of tissue insulin sensitivity in type 2 diabetes is a significant factor for sudden cardiac death. The complex pathophysiology stems from coexisting cardiovascular disease and complications of impaired tissue sensitivity to insulin. Long-term diabetics with underlying kidney disease and those requiring dialysis have systemic inflammation that adds to an increased risk of death. During times of pathological stress, myocardial tissue will express substrates and growth factors that cause conduction disequilibrium and predispose to sudden cardiac death. Diabetes is a modifiable risk factor in the prevention of sudden cardiac arrest. Specific prevention measures aimed towards lifestyle modification and medications are important to prevent diabetes and decrease mortality of future cardiac death. In recent times, drugs that compete with glucose in the proximal convoluted tubule of the nephron have clinical significance in lowering the risk of sudden cardiac arrest.

Predictive Value of Sirtuins in Acute Myocardial Infarction - Bridging the Bench to the Clinical Practice

Acute myocardial infarction (AMI) is a non-transmissible condition with high prevalence, morbidity, and mortality. Different strategies for the management of AMI are employed worldwide, but its early diagnosis remains a major challenge. Many molecules have been proposed in recent years as predictive agents in the early detection of AMI, including troponin (C, T, and I), creatine kinase MB isoenzyme, myoglobin, heart-type fatty acid-binding protein, and a family of histone deacetylases with enzymatic activities named sirtuins. Sirtuins may be used as predictive or complementary treatment strategies and the results of recent preclinical studies are promising. However, human clinical trials and data are scarce, and many issues have been raised regarding the predictive values of sirtuins. The present review summarizes research on the predictive value of sirtuins in AMI. We also briefly summarize relevant clinical trials and discuss future perspectives and possible clinical applications.

Genetic association study of a novel indel polymorphism in HSPA1B with the risk of sudden cardiac death in the Chinese populations

Sudden cardiac death (SCD) has become a global problem due to its high mortality in the general population. Identification of genetic factors predisposed to SCD is significant since it enables genetic testing that would contribute to molecular diagnosis and risk stratification of SCD. It has been reported that HSPA1B gene mutations might be related with SCD. In this study, based on candidate-gene-based approach and systematic screening strategy, a 5-base pair insertion/deletion (Indel) polymorphism (rs3036297) in the 3'UTR of HSPA1B gene was selected to perform a case-control study aiming to investigate its association with SCD susceptibility in Chinese populations. Logistic regression analysis showed that the insertion allele of rs3036297 was correlated with a comparatively lower risk for SCD [OR=0.58, 95%CI=0.43-0.77, P=1.28×10^-4] compared with the deletion allele. Luciferase activity assay indicated that HSPA1B expression could be regulated by rs3036297 through interfering binding with miR-134-5p. Furthermore, analysis of database from Haploreg and GTEx revealed that the rs3036297 variant was involved in potential cis-regulatory element with the promoter of HLA-DRB5 through a long-range interaction and the deletion allele of rs3036297 increased HLA-DRB5 expression. In conclusion, the rs3036297 variant may regulate HSPA1B expression via a mechanism of miRNA binding and HLA-DRB5 expression via a long-range promoter interaction through which contributed to SCD susceptibility. Therefore, rs3036297 would be a potential marker for molecular diagnosis and genetic counseling of SCD.

Systematic Meta-Analysis of the Association Between a Common NOS1AP Genetic Polymorphism, the QTc Interval, and Sudden Death

Contemporary studies have identified rs10494366 in the nitric oxide synthase 1 adaptor protein (NOS1AP) gene as a new genetic marker in modulating the QT interval and sudden cardiac death (SCD) in general populations. However, the conclusions were not coincident. Therefore, we conducted for the first time a system evaluation of the relativity of rs10494366, the QT interval, and sudden death by meta-analysis. In our study, the meta-analysis displayed the GG genotype of rs10494366 correlated with the QT interval in women with no heterogeneity, and in diabetes mellitus (DM) patients with minor heterogeneity. In the Caucasian population, the correlation of rs10494366 and sudden death was significant. The heterogeneity referred to the relevance between rs10494366 and sudden death in the Asian population. In conclusion, the minor allele of rs10494366 may have an impact on the QT interval in women or DM patients and may have a potential role in sudden death in the Caucasian population.

Usefulness of Single Nucleotide Polymorphisms as Predictors of Sudden Cardiac Death

The pathophysiology of sudden cardiac death (SCD) remains incompletely understood. Genetic mutations can create a favorable substrate for SCD. Our aim is to evaluate the evidence of single nucleotide polymorphisms (SNPs) as predictors of SCD. We searched the Medline database (2000 to 2017) and selected all case-control or cohort studies that reported associations between SNPs and SCD. Our search terms included "polymorphisms" and "sudden death." We collected the study design, population ethnic background, gene testing strategy, the association between the SNP and SCD, and the cardiovascular comorbidities of the population. Our search yielded 723 studies, of which we included 24 based upon our inclusion criteria. The studies had a total population of 78,165 participants, with a median age of 62.5 years (IQR 56 to 66) and 35% (IQR 13 to 32) were female. Almost all studies were conducted in white patients of European descent and the most commonly used genetic strategy was candidate gene panels. Fifteen of the studies had a case-control design that included SCD patients without known heart disease as the comparison group and the other 9 studies included patients with heart failure and coronary artery disease. The studies evaluated 53 SNPs and the most common genetic loci were SCN5A, RyR2, CASQ2, NOSA1P, and AGTR. SNPs with the 3 strongest statistically significant ORs >1 were: rs6684209 of CASQ2 (odds ratio [OR] 19), rs3814843 of CALM1 (OR 5.5), and rs35594137 of GJA5 (OR 3.6). In Conclusion, many SNPs are associated with SCD, with the strongest associations seen in SNPs of genes related to intracellular calcium handling. These findings were generated primarily using a candidate gene strategy in white patients with European descent.

Sudden Cardiac Death (SCD) - risk stratification and prediction with molecular biomarkers

Sudden cardiac death (SCD) is a sudden, unexpected death that is caused by the loss of heart function. While SCD affects many patients suffering from coronary artery diseases (CAD) and heart failure (HF), a considerable number of SCD events occur in asymptomatic individuals. Certain risk factors for SCD have been identified and incorporated in different clinical scores, however, risk stratification using such algorithms is only useful for health management rather than for early detection and prediction of future SCD events in high-risk individuals. In this review, we discuss different molecular biomarkers that are used for early detection of SCD. This includes genetic biomarkers, where the majority of them are genomic variants for genes that encode for ion channels. Meanwhile, protein biomarkers often denote proteins that play roles in pathophysiological processes that lead to CAD and HF, notably (i) atherosclerosis that involves oxidative stress and inflammation, as well as (ii) cardiac tissue damage that involves neurohormonal and hemodynamic regulation and myocardial stress. Finally, we outline existing challenges and future directions including the use of OMICS strategy for biomarker discovery and the multimarker panels.

Associations between common ion channel single nucleotide polymorphisms and sudden cardiac death in adults: A MOOSE-compliant meta-analysis

BACKGROUND

We sought to identify common ion channel single nucleotide polymorphisms (SNPs) associated with the occurrence of sudden cardiac death (SCD) to predict the incidence of SCD in clinical settings.

METHODS

This study involved a systematic review and meta-analysis of ion channel SNPs and risk of SCD in adults. We searched public databases for studies published up to September 19, 2017. We examined relationships between SNPs in common ion channel genes and the incidence of SCD.

RESULTS

We collected data for 22 trials that included a total of 4149 patients who experienced SCD or had a high risk of SCD and assessed these data in our meta-analysis. An allelic model showed that rs11720524 in SCN5A clearly protected against SCD (odds ratio [OR]: 0.76; 95% confidence interval [95% CI]: 0.67-0.85; P < .001). Subgroup analysis showed that rs11720524 in SCN5A protected against SCD in Europeans and Caucasians but not in Koreans. The allelic model indicated that rs12296050 in KCNQ1 also had significant protective effects against SCD (OR: 0.85; 95% CI: 0.76-0.96; P = .007). Moreover, this model demonstrated that rs2283222 in KCNQ1 had a significant negative relationship with SCD (OR: 0.73; 95% CI: 0.62-0.85; P < .001). Rs12296050 in KCNQ1 protected against SCD in Koreans and Americans. Our results also showed that rs790896 in RYR2 was negatively associated with SCD in a dominant model (OR: 0.66; 95% CI: 0.45-0.97; P = .033).

CONCLUSIONS

Rs11720524 in SCN5A is negatively related to SCD in Europeans and Caucasians, and rs12296050 and rs2283222 in KCNQ1 and rs790896 in RYR2 clearly have protective effects against SCD.

Soybean isoflavones ameliorate ischemic cardiomyopathy by activating Nrf2-mediated antioxidant responses

Ischemic cardiomyopathy (IC) is the major cause of heart failure. Conventional medicine has been proved ineffective with adverse effects. Soybean presents exciting adjunctive therapies and shows protective benefits for IC. However, the molecular mechanisms remain unclear. Isoflavones are the main bioactive components of soybean and may be protective against heart disease. Isoflavones were extracted by using an acidic-ethanol method and analyzed by HPLC. All patients with ischemic stroke were randomly and evenly assigned to two groups: the isoflavone group (80 mg day-1, n = 100) and control group (80 mg day-1 placebo, n = 100), and the whole period of the experiment was 24 weeks. The effects of soybean isoflavone on brachial flow-mediated dilatation (FMD) were measured. HPLC fractionation shows that isoflavone extracts are mainly composed of 55% genistein, 23% daidzein, and 14% glycitein. Isoflavone therapy reduced more levels of triglyceride and LDL-c in females than in males. FMD was higher in the isoflavone group than in the control group after 24-week therapy (treatment effect 2.0%, 95% CI 0.18-3.0, P = 0.01). The baseline differences were adjusted in FMD and the isoflavone therapies were closely associated with the reduction of FMD impairment at 24 weeks (odds ratio 0.30, 95% CI 0.14-0.85, P = 0.01). The effects of isoflavone on brachial FMD were negatively associated with base FMD (r = -0.65, P < 0.01). Furthermore, isoflavone therapy caused a significant increase in the levels of erythroid-derived 2-like 2 (Nrf2), superoxide dismutase (SOD) and a significant decrease in serum levels of C-reactive protein, 8-isoprostane, malondialdehyde, interleukin-6 and tumor necrosis factor alpha. In contrast, the isoflavones had no effects on the levels of oxidation-related molecules when Nrf2 was silenced. These results suggest that soybean isoflavones ameliorate IC patients by improving their antioxidant capacities via the upregulation of Nrf2.

A Common Variant in SCN5A and the Risk of Ventricular Fibrillation Caused by First ST-Segment Elevation Myocardial Infarction

BACKGROUND

Several common genetic variants have been associated with either ventricular fibrillation (VF) or sudden cardiac death (SCD). However, replication efforts have been limited. Therefore, we aimed to analyze whether such variants may contribute to VF caused by first ST-elevation myocardial infarction (STEMI).

METHODS

We analyzed 27 single nucleotide polymorphisms (SNP) previously associated with SCD/VF in other cohorts, and examined whether these SNPs were associated with VF caused by first STEMI in the GEnetic causes of Ventricular Arrhythmias in patients with first ST-elevation Myocardial Infarction (GEVAMI) study on ethnical Danes. The GEVAMI study is a prospective case-control study involving 257 cases (STEMI with VF) and 537 controls (STEMI without VF).

RESULTS

Of the 27 candidate SNPs, one SNP (rs11720524) located in intron 1 of SCN5A which was previously associated with SCD was significantly associated with VF caused by first STEMI. The major C-allele of rs11720524 was present in 64% of the cases and the C/C genotype was significantly associated with VF with an odds ratio (OR) of 1.87 (95% CI: 1.12-3.12; P = 0.017). After controlling for clinical differences between cases and controls such as age, sex, family history of sudden death, alcohol consumption, previous atrial fibrillation, statin use, angina, culprit artery, and thrombolysis in myocardial infarction (TIMI) flow, the C/C genotype of rs11720524 was still significantly associated with VF with an OR of 1.9 (95% CI: 1.05-3.43; P = 0.032). Marginal associations with VF were also found for rs9388451 in HEY2 gene. The CC genotype showed an insignificant risk for VF with OR = 1.50 (95% CI: 0.96-2.40; P = 0.070).

CONCLUSION

One common intronic variant in SCN5A suggested an association with VF caused by first STEMI. Further studies into the functional abnormalities associated with the noncoding variant in SCN5A may lead to important insights into predisposition to VF during STEMI.

KCNN2 polymorphisms and cardiac tachyarrhythmias

Potassium calcium-activated channel subfamily N member 2 (KCNN2) encodes an integral membrane protein that forms small-conductance calcium-activated potassium (SK) channels. Recent studies in animal models show that SK channels are important in atrial and ventricular repolarization and arrhythmogenesis. However, the importance of SK channels in human arrhythmia remains unclear. The purpose of the present study was to test the association between genetic polymorphism of the SK2 channel and the occurrence of cardiac tachyarrhythmias in humans. We enrolled 327 Han Chinese, including 72 with clinically significant ventricular tachyarrhythmias (VTa) who had a history of aborted sudden cardiac death (SCD) or unexplained syncope, 98 with a history of atrial fibrillation (AF), and 144 normal controls. We genotyped 12 representative tag single nucleotide polymorphisms (SNPs) across a 141-kb genetic region containing the KCNN2 gene; these captured the full haplotype information. The rs13184658 and rs10076582 variants of KCNN2 were associated with VTa in both the additive and dominant models (odds ratio [OR] 2.89, 95% confidence interval [CI] = 1.505-5.545, P = 0.001; and OR 2.55, 95% CI = 1.428-4.566, P = 0.002, respectively). After adjustment for potential risk factors, the association remained significant. The population attributable risks of these 2 variants of VTa were 17.3% and 10.6%, respectively. One variant (rs13184658) showed weak but significant association with AF in a dominant model (OR 1.91, CI = 1.025-3.570], P = 0.042). There was a significant association between the KCNN2 variants and clinically significant VTa. These findings suggest an association between KCNN2 and VTa; it also appears that KCNN2 variants may be adjunctive markers for risk stratification in patients susceptible to SCD.