The variation of the sarcolipin gene (SLN) in atrial fibrillation, long QT syndrome and sudden arrhythmic death syndrome

Nothing Regular about the Regulins: Distinct Functional Properties of SERCA Transmembrane Peptide Regulatory Subunits

The sarco-endoplasmic reticulum calcium ATPase (SERCA) is responsible for maintaining calcium homeostasis in all eukaryotic cells by actively transporting calcium from the cytosol into the sarco-endoplasmic reticulum (SR/ER) lumen. Calcium is an important signaling ion, and the activity of SERCA is critical for a variety of cellular processes such as muscle contraction, neuronal activity, and energy metabolism. SERCA is regulated by several small transmembrane peptide subunits that are collectively known as the “regulins”. Phospholamban (PLN) and sarcolipin (SLN) are the original and most extensively studied members of the regulin family. PLN and SLN inhibit the calcium transport properties of SERCA and they are required for the proper functioning of cardiac and skeletal muscles, respectively. Myoregulin (MLN), dwarf open reading frame (DWORF), endoregulin (ELN), and another-regulin (ALN) are newly discovered tissue-specific regulators of SERCA. Herein, we compare the functional properties of the regulin family of SERCA transmembrane peptide subunits and consider their regulatory mechanisms in the context of the physiological and pathophysiological roles of these peptides. We present new functional data for human MLN, ELN, and ALN, demonstrating that they are inhibitors of SERCA with distinct functional consequences. Molecular modeling and molecular dynamics simulations of SERCA in complex with the transmembrane domains of MLN and ALN provide insights into how differential binding to the so-called inhibitory groove of SERCA—formed by transmembrane helices M2, M6, and M9—can result in distinct functional outcomes.

Genetics of Atrial Fibrillation

Background

Atrial fibrillation (AF) is a common arrhythmia seen in clinical practice. Occasionally, no common risk factors are present in patients with this arrhythmia. This suggests the potential underlying role of genetic factors associated with predisposition to developing AF.

Methods and Results

We conducted a comprehensive review of the literature through large online libraries, including PubMed. Many different potassium and sodium channel mutations have been discussed in their relation to AF. There have also been non–ion channel mutations that have been linked to AF. Genome‐wide association studies have helped in identifying potential links between single‐nucleotide polymorphisms and AF. Ancestry studies have also highlighted a role of genetics in AF. Blacks with a higher percentage of European ancestry are at higher risk of developing AF. The emerging field of ablatogenomics involves the use of genetic profiles in their relation to recurrence of AF after catheter ablation.

Conclusions

The evidence for the underlying role of genetics in AF continues to expand. Ultimately, the role of genetics in risk stratification of AF and its recurrence is of significant interest. No established risk scores that are useful in clinical practice are present to date.

Genetic, Epigenetic and Transcription Factors in Atrial Fibrillation

Atrial fibrillation (AF) is one of the most common arrhythmia that occurs in patients with cardiovascular diseases. Congenital forms of AF are quite rare. Many studies have shown that genetic, epigenetic and transcription factors may play an important role in the development and the progression of AF. In our review, studies have been conducted on the identification of mutations in ionic and non-ionic channels, possibly associated with AF. These mutations were found only in isolated groups of patients with AF, and in general, monogenic forms of AF are a rare subtype of the disease. Genomic association studies have helped to identify potential links between single nucleotide polymorphisms and AF. The risk of AF in the general population is likely to be determined by the interaction between environmental factors and many alleles. In recent years, the emergence of a genome-wide associative studies has significantly expanded the understanding of the genetic basis for the inheritance of AF and has led to the emergence of new evidence of the important role of genetic factors in the development of AF, in the risk stratification of AF and the recurrence of AF. Epigenetic factors are also important in AF. Epigenetic therapy aimed at treating a disease through exposure to epigenome is currently under development. A newly emerged area of ablatogenomics includes the use of genetic profiles that allow assessing the likelihood of recurrence of AF after catheter ablation. The results of genetic studies in AF show that, in addition to their role in the appearance of congenital heart pathologies, transcription factors play an important role in the pathogenesis of AF.

Is endothelin gene polymorphism associated with postoperative atrial fibrillation in patients undergoing coronary artery bypass grafting?

BACKGROUND

The mechanism of development of atrial fibrillation (AF) in patients undergoing coronary artery bypass grafting (CABG) has not been clearly defined, and the involvement of multiple factors such as advanced age, withdrawal of β-blockers, inadequate atrial protection, and electrolyte imbalance, particularly hypomagnesemia has been documented by several authors. Despite all the available pharmacologic prophylaxis, incidence of AF still remains high in this group of patients. This unexplained cause could be genetic inheritance of endothelin-1 (ET-1) gene which is thought to have a pro-arrhythmogenic effect.

AIM

This study aims to investigate the relationship between plasma ET-1 concentrations, ET-1 gene polymorphisms in loci -1370 T/G, -134 (3A/4A) Ins/del, Lys198Asn (G/T), and occurrence of AF in patients undergoing CABG.

METHODOLOGY

Ninety-eight nonrelated, nondiabetic patients over a period of 4 years undergoing routine CABG were selected for the present study. All patients were genotyped for three single nucleotide polymorphisms (SNPs) in loci -1370 T/G, -134 (3A/4A) Ins/del, and Lys198Asn (G/T) in the ET-1 gene by gene sequencing. The plasma ET-1 concentrations were measured using an ET immunoassay.

RESULTS

Plasma ET-1 concentrations were higher in AF+ group (P = 0.001) as compared to AF- group. The allele frequencies between AF+ and AF- group were significantly different only with respect to the Lys198Asn (G/T) SNP of the ET-1 gene.

CONCLUSION

The study described the possible correlation of polymorphism of ET gene in CABG population from India. The ET-1 gene might play a disease-modifying role in atrial fibrillation.

Genetic Discoveries in Atrial Fibrillation and Implications for Clinical Practice

Atrial fibrillation (AF) is an arrhythmia with a genetic basis. Over the past decade, rapid advances in genotyping technology have revolutionised research regarding the genetic basis of AF. While AF genetics research was previously largely restricted to familial forms of AF, recent studies have begun to characterise the genetic architecture underlying the form of AF encountered in everyday clinical practice. These discoveries could have a significant impact on the management of AF. However, much work remains before genetic findings can be translated to clinical practice. This review summarises results of studies in AF genetics to date and discusses the potential implications of these findings in clinical practice.

Emerging roles of junctophilin-2 in the heart and implications for cardiac diseases

Cardiomyocytes rely on a highly specialized subcellular architecture to maintain normal cardiac function. In a little over a decade, junctophilin-2 (JPH2) has become recognized as a cardiac structural protein critical in forming junctional membrane complexes (JMCs), which are subcellular domains essential for excitation-contraction coupling within the heart. While initial studies described the structure of JPH2 and its role in anchoring junctional sarcoplasmic reticulum and transverse-tubule (T-tubule) membrane invaginations, recent research has an expanded role of JPH2 in JMC structure and function. For example, JPH2 is necessary for the development of postnatal T-tubule in mammals. It is also critical for the maintenance of the complex JMC architecture and stabilization of local ion channels in mature cardiomyocytes. Loss of this function by mutations or down-regulation of protein expression has been linked to hypertrophic cardiomyopathy, arrhythmias, and progression of disease in failing hearts. In this review, we summarize current views on the roles of JPH2 within the heart and how JPH2 dysregulation may contribute to a variety of cardiac diseases.

Atrial fibrillation from the pathologist's perspective

Atrial fibrillation (AF), the most common sustained cardiac arrhythmia encountered in clinical practice, is associated with increased morbidity and mortality. Electrophysiologically, it is characterized by a high rate of asynchronous atrial cell depolarization causing a loss of atrial contractile function and irregular ventricular rates. For a long time, AF was considered as a pure functional disorder without any structural background. Only in recent years, have new mapping and imaging techniques identified atrial locations, which are very often involved in the initiation and maintenance of this supraventricular arrhythmia (i.e. the distal portion of the pulmonary veins and the surrounding atrial myocardium). Morphological analysis of these myocardial sites has demonstrated significant structural remodeling as well as paved the way for further knowledge of AF natural history, pathogenesis, and treatment. This architectural myocardial disarrangement is induced by the arrhythmia itself and the very frequently associated cardiovascular disorders. At the same time, the structural remodeling is also capable of sustaining AF, thereby creating a sort of pathogenetic vicious circle. This review focuses on current understanding about the structural and genetic bases of AF with reference to their classification, pathogenesis, and clinical implications.

Variations in the human soluble epoxide hydrolase gene and recurrence of atrial fibrillation after catheter ablation

BACKGROUND

Single nucleotide polymorphisms (SNPs) of EPHX2 alter sEH activity and are associated with increased [rs41507953 (K55R)] or reduced [rs751141 (R287Q)] cardiovascular risk via modulation of fibrosis, inflammation or cardiac ion channels. This indicates an effect on development and therapy response of AF. This study tested the hypothesis that variations in the EPHX2 gene encoding human soluble epoxide hydrolase (sEH) are associated with atrial fibrillation (AF) and recurrence of atrial fibrillation after catheter ablation.

METHODS AND RESULTS

A total of 218 consecutive patients who underwent catheter ablation for drug refractory AF and 268 controls were included. Two SNPs, rs41507953 and rs751141, were genotyped by direct sequencing. In the ablation group, holter recordings 3, 12 and 24 months after ablation were used to detect AF recurrence. No significant association of the SNPs and AF at baseline was detected. In the ablation group, recurrence of AF occurred in 20% of the patients 12 months after ablation and in 35% 24 months after ablation. The presence of the rs751141 polymorphism significantly increased the risk of AF recurrence 12 months (odds ratio [OR]: 3.2, 95% confidence interval [CI]: 1.237 to 8.276, p=0.016) and 24 months (OR: 6.076, 95% CI: 2.244 to 16.451, p<0.0001) after catheter ablation.

CONCLUSIONS

The presence of rs751141 polymorphism is associated with a significantly increased risk of AF recurrence after catheter ablation. These results point to stratification of catheter ablation by genotype and differential use of sEH-inhibitory drugs in the future.

The genetics of atrial fibrillation: from the bench to the bedside

Atrial fibrillation (AF) has become a growing global epidemic and a financial burden for society. The past 10 years have seen significant advances in our understanding of the genetic aspects of AF: At least 2 chromosomal loci and 17 causal genes have been identified in familial AF, and an additional 7 common variants and single-nucleotide polymorphisms in 11 different genes have been indicated in nonfamilial AF. However, the current management strategies for AF are suboptimal. The integration of genetic information into clinical practice may aid the early identification of AF patients who are at risk as well as the characterization of molecular pathways that culminate in AF, with the eventual result of better treatment. Never before has such an opportunity arisen to advance our understanding of the biology of AF through the translation of genetics findings from the bench to the bedside.

Recent advances in the molecular pathophysiology of atrial fibrillation

Atrial fibrillation (AF) is an extremely common cardiac rhythm disorder that causes substantial morbidity and contributes to mortality. The mechanisms underlying AF are complex, involving both increased spontaneous ectopic firing of atrial cells and impulse reentry through atrial tissue. Over the past ten years, there has been enormous progress in understanding the underlying molecular pathobiology. This article reviews the basic mechanisms and molecular processes causing AF. We discuss the ways in which cardiac disease states, extracardiac factors, and abnormal genetic control lead to the arrhythmia. We conclude with a discussion of the potential therapeutic implications that might arise from an improved mechanistic understanding.

Genetics of atrial fibrillation and possible implications for ischemic stroke

Atrial fibrillation is the most common cardiac arrhythmia mainly caused by valvular, ischemic, hypertensive, and myopathic heart disease. Atrial fibrillation can occur in families suggesting a genetic background especially in younger subjects. Additionally recent studies have identified common genetic variants to be associated with atrial fibrillation in the general population. This cardiac arrhythmia has important public health implications because of its main complications: congestive heart failure and ischemic stroke. Since atrial fibrillation can result in ischemic stroke, one might assume that genetic determinants of this cardiac arrhythmia are also implicated in cerebrovascular disease. Ischemic stroke is a multifactorial, complex disease where multiple environmental and genetic factors interact. Whether genetic variants associated with a risk factor for ischemic stroke also increase the risk of a particular vascular endpoint still needs to be confirmed in many cases. Here we review the current knowledge on the genetic background of atrial fibrillation and the consequences for cerebrovascular disease.

Monogenic atrial fibrillation as pathophysiological paradigms

Atrial fibrillation (AF) is the most common cardiac rhythm abnormality and represents a major burden, both to patients and to health-care systems. In recent years, increasing evidence from population-based studies has demonstrated that AF is a heritable condition. Although familial forms of AF have been recognized for many years, they represent a rare subtype of the arrhythmia. However, despite their limited prevalence, the identification of mutations in monogenic AF kindreds has provided valuable insights into the molecular pathways underlying the arrhythmia and a framework for investigating AF encountered in the general population. In contrast to these rare families, the typical forms of AF occurring in the community are likely to be multigenic and have significant environmental influences. Recently, genome-wide association studies have uncovered common sequence variants that confer increased susceptibility to the arrhythmia. In the future, the elucidation of the genetic substrate underlying both familial and more typical forms of AF will hopefully lead to the development of novel diagnostic tools as well as more targeted rhythm control strategies. In this article, we will focus on monogenic forms of AF and also provide an overview of case-control association studies for AF.

Lack of replication in polymorphisms reported to be associated with atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most common sustained arrhythmia and has a substantial heritable component. Numerous associations between single nucleotide polymorphisms (SNPs) and AF have been described, but few have been replicated.

OBJECTIVE

We sought to systematically replicate SNPs that are reported to be associated with AF in two large study samples of European descent.

METHODS

We searched PubMed for studies reporting associations between SNPs and AF published before July 1, 2007. SNPs were genotyped in two independent case-control samples from Germany and the United States. Associations between SNPs and AF were assessed using logistic regression models adjusting for age, sex, and hypertension. A meta-analysis of the results from the two studies was performed.

RESULTS

We identified 21 SNPs and the angiotensin-converting enzyme insertion/deletion polymorphism that were reported to be associated with AF in the literature. Nine of these genetic variants were not represented on common genome-wide SNP arrays. We successfully genotyped 21 of these 22 variants in 2,145 cases with AF from the German Competence Network for Atrial Fibrillation and 4,073 controls from the KORA S4 study and 16 variants in 790 cases and 1,330 controls from the Massachusetts General Hospital. None of the SNPs replicated in independent populations with AF.

CONCLUSION

Our results suggest that previously reported associations to AF were likely false positives and highlight the need for systematic replication of genetic associations in large, independent cohorts to accurately detect variants associated with disease.

Different aspects of atrial fibrillation genetics

Atrial fibrillation (AF) is a consequence of a complex interplay of genetic, epigenetic and environmental factors. In addition, AF is a major contributor to stroke, heart failure, and mortality. Several family studies have shown a strong polygenetic predisposition for AF but, so far, most of the linkage analysis and candidate gene studies have discovered only monogenic, rare, deleterious mutations. While research in human genetics has moved from monogenic to oligogenic to complex diseases, its pharmacogenetics branch has followed, usually a few years behind. The present paper reviews the potential contributions of genetic approaches to AF.

Genetics of atrial fibrillation

Recent studies of atrial fibrillation (AF) have identified mutations in a series of ion channels; however, these mutations appear to be relatively rare causes of AF. A genome-wide association study has identified novel variants on chromosome 4 associated with AF, although the mechanism of action for these variants remains unknown. Ultimately, a greater understanding of the genetics of AF should yield insights into novel pathways, therapeutic targets, and diagnostic testing for this common arrhythmia.

Genetics of atrial fibrillation

Recent studies of AF have identified mutations in a series of ion channels; however, these mutations appear to be relatively rare causes of AF. A genome-wide association study has identified novel variants on chromosome 4 associated with AF, although the mechanism of action for these variants remains unknown. Ultimately, a greater understanding of the genetics of AF should yield insights into novel pathways, therapeutic targets, and diagnostic testing for this common arrhythmia.

Molecular genetics of atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. There is genetic predisposition for the development of AF. Recently, by linkage analysis, several loci have been mapped for monogenetic AF, including 11p15.5, 21q22, 17q, 7q35-36, 5p13, 6q14-16, and 10q22. Some of these loci encode for subunits of potassium channels (KCNQ1, KCNE2, KCNJ2, and KCNH2 genes), and the remaining are yet unidentified. All of the known mutations are associated with a gain of function of repolarization potassium currents, resulting in a shortening of action potential duration and atrial refractory period, which facilitate multiple re-entrant circuits in AF. In addition to familial AF, common AF often occurs in association with acquired diseases such as hypertension, valvular heart disease, and heart failure. By genetic association study, some genetic variants or polymorphisms related to the mechanism of AF have been found to be associated with common AF, including genes encoding for subunits of potassium or sodium channels, sarcolipin gene, renin-angiotensin system gene, connexin-40 gene, endothelial nitric oxide synthase gene, and interleukin-10 gene. These observations suggest that genes related to ionic channels, calcium handling protein, fibrosis, conduction and inflammation play important roles in the pathogenesis of common AF. The complete elucidation of genetic loci for common AF is still in its infancy. However, the availability of genomewide scans with hundreds or thousands of polymorphisms has made it possible. However, challenges and pitfalls exist in association studies, and consideration of particular features of study design is necessary before making definite conclusions from these studies.

Atrial fibrillation: evidence for genetically determined disease

PURPOSE OF REVIEW

Atrial fibrillation is traditionally regarded as a sporadic, nongenetic disorder. Nevertheless, recent growing evidence points to an important heritable basis for atrial fibrillation, with significant genetic determinants. This paper reviews recent progress in understanding the role of genetic contributors to the pathogenesis of atrial fibrillation and its familial susceptibility.

RECENT FINDINGS

Population-based studies have demonstrated a significant heritable component in atrial fibrillation, with specific contributors including single-gene mutations and single-nucleotide polymorphisms. Variants in both ion-channel and nonion-channel genes have been identified as potential atrial fibrillation-risk determinants. In addition, studies have pointed to interesting combined roles of genetic and environmental factors in atrial fibrillation pathogenesis, providing insights into gene-environment interactions. Clinical studies suggest that individual genetic profiles may determine the therapeutic response of atrial fibrillation.

SUMMARY

Rapidly evolving work indicates that there are important genetic determinants of atrial fibrillation, and suggests that understanding these determinants will help us both to appreciate better the underlying pathophysiology and to provide new approaches in diagnosis, prevention and treatment of this common cardiac condition.