Genetic Variants Associated With Susceptibility to Atrial Fibrillation in a Japanese Population

Polygenic risk scores in atrial fibrillation: Associations and clinical utility in disease prediction

Atrial fibrillation (AF) is a common heart arrhythmia and a major cause of cardioembolic stroke. Therefore, accurate prediction is desirable to allow high-risk individuals to be identified early and their risk lowered before complications arise. Polygenic risk scores (PRSs) have become a popular method of quantifying aggregated genetic risk from common variants, but their clinical value in AF remains uncertain. This literature review summarizes the associations between PRS and AF risk and discusses the evidence for the clinical utility of PRS for AF prediction. Stroke risk in patients with AF is also considered. Despite consistent associations between PRS and AF risk, the performance of PRS as a stand-alone tool for AF prediction was poor. However, addition of PRS to the existing AF prediction models commonly improved the predictive performance above that of the clinical models alone, including in cohorts with comorbid cardiovascular disease. Associations between PRS and cardioembolic stroke risk in patients with AF have also been reported, but improvements in stroke prediction models from PRS have been minimal. PRS are likely to add value to the existing clinical AF prediction models; however, standardization of PRS across studies and populations will likely be required before they can be meaningfully adopted into routine clinical practice.

Risk stratification of atrial fibrillation and stroke using single nucleotide polymorphism and circulating biomarkers

BACKGROUND

Atrial fibrillation (AF) is the most common sustained arrhythmia, and it causes a high rate of complications such as stroke. It is known that AF begins as paroxysmal form and gradually progresses to persistent form, and sometimes it is difficult to identify paroxysmal AF (PAF) before having stroke. The aim of this study is to evaluate the risk of PAF and stroke using genetic analysis and circulating biomarkers.

MATERIALS AND METHODS

A total of 600 adult subjects were enrolled (300 from PAF and control groups). Peripheral blood was drawn to identify the genetic variation and biomarkers. Ten single nucleotide polymorphisms (SNPs) were analyzed, and circulating cell-free DNA (cfDNA) was measured from plasma. Four microRNAs (miR-99a-5p, miR-192-5p, miR-214-3p, and miR-342-5p) were quantified in serum using quantitative RT-PCR.

RESULTS

Genotyping identified 4 single nucleotide polymorphisms (SNPs) that were significantly associated with AF (rs6817105, rs3807989, rs10824026, and rs2106261), and the genetic risk score using 4 SNPs showed the area under the curve (AUC) of 0.631. Circulating miRNAs and cfDNA did not show significant differences between PAF and control groups. The concentration of cfDNA was significantly higher in patients with a history of stroke, and the AUC was 0.950 to estimate the association with stroke.

CONCLUSION

The risk of AF could be assessed by genetic risk score. Furthermore, the risk of stroke might be evaluated by plasma cfDNA level.

Genetic risk factors for postoperative atrial fibrillation-a nationwide genome-wide association study (GWAS)

Background

Atrial fibrillation (AF) is a major cause of morbidity with a high prevalence among the elderly and has an established genetic disposition. Surgery is a well-known risk factor for AF; however, it is currently not recognized how much common genetic variants influence the postoperative risk. The purpose of this study was to identify Single Nucleotide Polymorphisms associated with postoperative AF.

Methods

The UK Biobank was utilized to conduct a Genome-Wide Association Study (GWAS) to identify variants associated with AF after surgery. An initial discovery GWAS was performed in patients that had undergone surgery with subsequent replication in a unique non-surgical cohort. In the surgical cohort, cases were defined as newly diagnosed AF within 30 days after surgery. The threshold for significance was set at 5 × 10^-8.

Results

After quality control, 144,196 surgical patients with 254,068 SNPs were left for analysis. Two variants (rs17042171 (p = 4.86 × 10^-15) and rs17042081 (p = 7.12 × 10^-15)) near the PITX2-gene reached statistical significance. These variants were replicated in the non-surgical cohort (1.39 × 10^-101 and 1.27 × 10^-93, respectively). Several other loci were significantly associated with AF in the non-surgical cohort.

Conclusion

In this GWAS-analysis of a large national biobank, we identified 2 variants that were significantly associated with postoperative AF. These variants were subsequently replicated in a unique non-surgical cohort. These findings bring new insight in the genetics of postoperative AF and may help identify at-risk patients and guide management.

Influence of ZFHX3 Polymorphisms on the Risk of Ischemic Stroke in Chinese Han Population

The association of ZFHX3 gene polymorphisms with ischemia stroke (IS) susceptibility has been clarified in Europeans, but not in the Chinese Han population. To assess the effect of ZFHX3 polymorphisms on IS risk, rs7193343, rs879324, and rs12932445 were selected and genotyped using the Agena MassARRAY platform in 694 patients and 687 healthy controls. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by logistic regression model adjusted for age, sex, smoking, and drinking status. The potentially influential factors for IS risk were analyzed using multifactor dimension reduction (MDR) software v3.0.2 and least absolute shrinkage and selection operator (LASSO) logistic regression. Our results displayed that rs879324 (p = 0.011, OR = 0.81) and rs12932445 (p = 0.012, OR = 0.81) were protective factors for IS in the Chinese Han population. Specifically, rs879324 had a lower susceptibility to IS in subjects aged ≤ 64 years, non-smokers, and non-drinkers (p < 0.05). Furthermore, rs12932445 was associated with a reduced risk of IS in people aged > 64 years, females, non-smokers, and non-drinkers (p < 0.05). MDR and LASSO analyses revealed that rs879324 was the most influential factor for IS risk. These findings suggested that ZFHX3 variants may be biomarkers in IS occurrence in the Chinese Han population, which may provide a new insight into the etiology of IS.

Regulation of cardiac ion channels by transcription factors: Looking for new opportunities of druggable targets for the treatment of arrhythmias

Cardiac electrical activity is governed by different ion channels that generate action potentials. Acquired or inherited abnormalities in the expression and/or function of ion channels usually result in electrophysiological changes that can cause cardiac arrhythmias. Transcription factors (TFs) control gene transcription by binding to specific DNA sequences adjacent to target genes. Linkage analysis, candidate-gene screening within families, and genome-wide association studies have linked rare and common genetic variants in the genes encoding TFs with genetically-determined cardiac arrhythmias. Besides its critical role in cardiac development, recent data demonstrated that they control cardiac electrical activity through the direct regulation of the expression and function of cardiac ion channels in adult hearts. This narrative review summarizes some studies showing functional data on regulation of the main human atrial and ventricular Na⁺, Ca²⁺, and K⁺ channels by cardiac TFs such as Pitx2c, Tbx20, Tbx5, Zfhx3, among others. The results have improved our understanding of the mechanisms regulating cardiac electrical activity and may open new avenues for therapeutic interventions in cardiac acquired or inherited arrhythmias through the identification of TFs as potential drug targets. Even though TFs have for a long time been considered as 'undruggable' targets, advances in structural biology have led to the identification of unique pockets in TFs amenable to be targeted with small-molecule drugs or peptides that are emerging as novel therapeutic drugs.

Transcriptional factors in calcium mishandling and atrial fibrillation development

Healthy cardiac conduction relies on the coordinated electrical activity of distinct populations of cardiomyocytes. Disruption of cell-cell conduction results in cardiac arrhythmias, a leading cause of morbidity and mortality worldwide. Recent genetic studies have highlighted a major heritable component and identified numerous loci associated with risk of atrial fibrillation, including transcription factor genes, particularly those important in cardiac development, microRNAs, and long noncoding RNAs. Identification of such genetic factors has prompted the search to understand the mechanisms that underlie the genetic component of AF. Recent studies have found several mechanisms by which genetic alterations can result in AF formation via disruption of calcium handling. Loss of developmental transcription factors in adult cardiomyocytes can result in disruption of SR calcium ATPase, sodium calcium exchanger, calcium channels, among other ion channels, which underlie action potential abnormalities and triggered activity that can contribute to AF. This review aims to summarize the complex network of transcription factors and their roles in calcium handling.

Predicting atrial fibrillation using a combination of genetic risk score and clinical risk factors

BACKGROUND

Atrial fibrillation (AF) has a genetic basis, and environmental factors can modify its actual pathogenesis.

OBJECTIVE

The purpose of this study was to construct a combined risk assessment method including both genetic and clinical factors in the Japanese population.

METHODS

We screened a cohort of 540 AF patients and 520 non-AF controls for single nucleotide polymorphisms (SNPs) previously associated with AF by genome-wide association studies. The most strongly associated SNPs after propensity score analysis were then used to calculate a weighted genetic risk score (WGRS). We also enrolled 1018 non-AF Japanese subjects as a validation cohort and monitored AF emergence over several years. Finally, we constructed a logistic model for AF prediction combining WGRS and clinical risk factors.

RESULTS

We identified 5 SNPs (in PRRX1, ZFHX3, PITX2, HAND2, and NEURL1) associated with AF after Bonferroni correction. There was a 4.92-fold difference in AF risk between the highest and lowest WGRS calculated using these 5 SNPs (P = 2.32 × 10^-10). Receiver operating characteristic analysis of WGRS yielded an area under the curve (AUC) of 0.73 for the screening cohort and 0.72 for the validation cohort. The predictive logistic model constructed using a combination of WGRS and AF clinical risk factors (age, body mass index, sex, and hypertension) demonstrated better discrimination of AF than WGRS alone (AUC = 0.84; sensitivity 75.4%; specificity 80.2%).

CONCLUSION

This novel predictive model of combined AF-associated SNPs and known clinical risk factors can accurately stratify AF risk in the Japanese population.

Genetic variants associated with atrial fibrillationand long-term recurrence after catheter ablation for atrialfibrillation in Turkish patients

OBJECTIVE

Genome-wide association studies have revealed that single nucleotide polymorphisms (SNPs) are associated with atrial fibrillation (AF) and can predict AF recurrence after catheter ablation in different populations. However, there exists no such data for the Turkish population. We aimed to investigate whether 11 SNPs in the PITX2, ZFHX3, EPHX2, CAV1, TBX5, TGF-1, and SCN10A were related to AF and whether these SNPs can predict long-term atrial tachyarrhythmia (ATa) recurrence after pulmonary vein isolation (PVI) for AF in Turkish patients.

METHODS

A total of 245 consecutive patients with non-valvular AF (44.9% men, mean age: 60.2±13.2 years, 65.3% paroxysmal AF) and 50 age- and sex-matched controls were included in this analysis. The clinical features and genetic variants were compared between the 2 groups. Of the 245 patients, 128 who underwent PVI with second-generation cryoballoon were further examined for long-term recurrence after the procedure.

RESULTS

Four SNPs in PITX2 were significantly associated with AF (rs10033464_T: OR 3.29, 95%CI: 1.38-7.82, p=0.007; rs6838973_T: OR 3.06, 95% CI 1.36-6.87, p=0.007; rs3853445_C: OR 2.84, 95%CI: 1.27-6.36, p=0.011; rs17570669_T: OR 4.03, 95% CI: 1.71-9.51, p=0.001). Among these patients who underwent PVI, one locus in CAV1 (rs3807989_G: OR 4.50, 95% CI 1.04-19.31, p=0.043) and early recurrence (OR: 8.06, 95% CI: 2.12-30.55, p=0.002) predicted long-term AF recurrence after catheter ablation.

CONCLUSION

Significant associations exists between 4 SNPs in PITX2 and AF (rs10033464, rs6838973, rs3853445, and rs17570669) in Turkish patients. In addition, 1 genetic variant in CAV1 (rs3807989) and early recurrence can predict long-term ATa recurrence after catheter ablation.

The genetic underpinnings of variation in ages at menarche and natural menopause among women from the multi-ethnic Population Architecture using Genomics and Epidemiology (PAGE) Study: A trans-ethnic meta-analysis

Current knowledge of the genetic architecture of key reproductive events across the female life course is largely based on association studies of European descent women. The relevance of known loci for age at menarche (AAM) and age at natural menopause (ANM) in diverse populations remains unclear. We investigated 32 AAM and 14 ANM previously-identified loci and sought to identify novel loci in a trans-ethnic array-wide study of 196,483 SNPs on the MetaboChip (Illumina, Inc.). A total of 45,364 women of diverse ancestries (African, Hispanic/Latina, Asian American and American Indian/Alaskan Native) in the Population Architecture using Genomics and Epidemiology (PAGE) Study were included in cross-sectional analyses of AAM and ANM. Within each study we conducted a linear regression of SNP associations with self-reported or medical record-derived AAM or ANM (in years), adjusting for birth year, population stratification, and center/region, as appropriate, and meta-analyzed results across studies using multiple meta-analytic techniques. For both AAM and ANM, we observed more directionally consistent associations with the previously reported risk alleles than expected by chance (p-values_binomial≤0.01). Eight densely genotyped reproductive loci generalized significantly to at least one non-European population. We identified one trans-ethnic array-wide SNP association with AAM and two significant associations with ANM, which have not been described previously. Additionally, we observed evidence of independent secondary signals at three of six AAM trans-ethnic loci. Our findings support the transferability of reproductive trait loci discovered in European women to women of other race/ethnicities and indicate the presence of additional trans-ethnic associations both at both novel and established loci. These findings suggest the benefit of including diverse populations in future studies of the genetic architecture of female growth and development.

A Common Variation in the Caveolin 1 Gene Is Associated with High Serum Triglycerides and Metabolic Syndrome in an Admixed Latin American Population

Background: The caveolin 1 (CAV1) gene has been associated with metabolic traits in animal models and human cohorts. Recently, a prevalent variant in CAV1 has been found to be related to metabolic syndrome in Hispanics living in North America. Since Hispanics represent an admixed population at high risk for cardiovascular diseases, in this study a Latin American population with a similar genetic background was assessed.

Objective: To analyze a genetic association between CAV1 and metabolic traits in an admixed Latin American population.

Methods: A cross-sectional study was carried out with adults from the Colombian Caribbean Coast, selected in urban clusters and work places through a stratified sampling to include diverse ages and socioeconomic groups. Blood pressure and waist circumference were registered. Serum concentrations of glucose, triglycerides, and high-density lipoprotein cholesterol were measured from an 8-hr fasting whole-blood sample. Two previously analyzed CAV1 single nucleotide polymorphisms were genotyped (rs926198 and rs11773845). A logistic regression model was applied to estimate the associations. An admixture adjustment was performed through a Bayesian model.

Results: A total of 605 subjects were included. rs11773845 was associated with hypertriglyceridemia [odds ratio (OR) = 1.33, p = 0.001] and the metabolic syndrome (OR = 1.53, p = 0.02). When admixture adjustment was performed these genetic associations preserved their statistical significance. There were no significant associations between rs926198 and metabolic traits.

Conclusions: The CAV1 variation rs11773845 was found to be consistently associated with high serum triglycerides and the metabolic syndrome. This is the first report of a relationship between CAV1 variants and serum triglycerides in Latin America.

PITX2 deficiency and associated human disease: insights from the zebrafish model

The PITX2 (paired-like homeodomain 2) gene encodes a bicoid-like homeodomain transcription factor linked with several human disorders. The main associated congenital phenotype is Axenfeld-Rieger syndrome, type 1, an autosomal dominant condition characterized by variable defects in the anterior segment of the eye, an increased risk of glaucoma, craniofacial dysmorphism and dental and umbilical anomalies; in addition to this, one report implicated PITX2 in ring dermoid of the cornea and a few others described cardiac phenotypes. We report three novel PITX2 mutations-c.271C > T, p.(Arg91Trp); c.259T > C, p.(Phe87Leu); and c.356delA, p.(Gln119Argfs*36)-identified in independent families with typical Axenfeld-Rieger syndrome characteristics and some unusual features such as corneal guttata, Wolf-Parkinson-White syndrome, and hyperextensibility. To gain further insight into the diverse roles of PITX2/pitx2 in vertebrate development, we generated various genetic lesions in the pitx2 gene via TALEN-mediated genome editing. Affected homozygous zebrafish demonstrated congenital defects consistent with the range of PITX2-associated human phenotypes: abnormal development of the cornea, iris and iridocorneal angle; corneal dermoids; and craniofacial dysmorphism. In addition, via comparison of pitx2M64* and wild-type embryonic ocular transcriptomes we defined molecular changes associated with pitx2 deficiency, thereby implicating processes potentially underlying disease pathology. This analysis identified numerous affected factors including several members of the Wnt pathway and collagen types I and V gene families. These data further support the link between PITX2 and the WNT pathway and suggest a new role in regulation of collagen gene expression during development.

Genetics of atrial fibrillation

PURPOSE OF REVIEW

Atrial fibrillation is a common cardiac arrhythmia with a high morbidity and mortality affecting 34 million worldwide. Current therapies are inadequate and often fail to directly address molecular mechanisms of the disease. In this review, we will provide an overview of recent advances in our understanding of the genetic underpinnings of atrial fibrillation.

RECENT FINDINGS

Large-scale genetic association studies have more than doubled the number of genetic loci associated with atrial fibrillation during the last year. Studies examining how genes at or near these loci can affect the pathogenesis of atrial fibrillation are ongoing in cellular, animal, and computational models. In addition, several recent clinical studies have also demonstrated that variants at these loci can aid in risk stratification of patients.

SUMMARY

There are now over 30 genetic loci associated with atrial fibrillation. A better understanding of how these loci relate to disease pathogenesis may provide insight into novel therapeutic targets and ultimately lead to improved clinical care.