Positional Cloning and Candidate Gene Approach to Familial Atrial Fibrilation

描述（由申请人提供）：房颤（AF）是成人中最常见的持续性心律失常，与显著的发病率和死亡率增加相关。虽然房颤的危险因素是多因素的，但约30%的房颤患者与潜在的心脏或全身性疾病无关（“单发”房颤）。在过去的十年里，我们和其他人已经证明，单发房颤具有实质性的遗传基础。人类心脏钠通道负责心脏动作电位（AP）的快速上升，而由SCN5A编码的典型钠通道Nav1.5的阻滞剂具有抗心律失常作用。我们和其他人已经表明，SCN5A突变可引起一系列心脏通道病变，包括以晚期钠电流（INa-L）增强、AP持续时间延长和早期后去极化为特征的心房纤颤。全基因组关联研究（GWAS）表明，由SCN10A编码的第二个钠通道Nav1.8与房颤易感性有关。我们已经在单发房颤患者中发现了多个罕见的SCN10A变异。这提出了一个假设，在这里进行验证，即SCN10A的罕见变异与房颤有关。在Specific Aim 1中，我们将进行一项病例对照遗传关联研究，以确定是否先天罕见的潜在致病性SCN10A变异在单发房颤先证者中比在对照组中富集。此外，我们将确定每个罕见的SCN10A变异携带者的扩展家系，以确定AF的家族聚集性，并确定基因型-表型相关性。罕见的SCN10A变异是高度保守的，预计是有害的，并与AF聚集，将通过在背根神经节细胞系中表达它们来确定峰值和INa-L的功能特征。罕见SCN10A变异的体外功能表征将使其与af相关，并可能为心律失常的潜在遗传机制提供新的见解。此外，这些研究也有可能揭示Nav1.8作为抗心律失常干预的新治疗靶点。在该奖项的前一个周期中，我们使用位置克隆和候选基因方法来鉴定编码心脏离子通道和信号蛋白的基因，这些基因对心律失常具有很大的风险。相比之下，GWAS已经确定了常见的AF易感位点，但效果不大。虽然这些方法对房颤的遗传结构提供了重要的见解，但总的来说，它们只解释了房颤遗传能力的一小部分。这就提出了一种假设，即罕见的变异与适度的遗传有关

DESCRIPTION (provided by applicant): Atrial fibrillation (AF), the most common sustained cardiac arrhythmia in adults, is associated with significant morbidity and increased mortality. While risk factors for AF are multifactorial, ~30% of patients have AF that is unassociated with underlying heart or systemic disease ('lone' AF). Over the last decade, we and others have shown that lone AF has a substantial genetic basis. The human cardiac sodium channel is responsible for the rapid upstroke of the cardiac action potential (AP) and blockers of Nav1.5, the canonical sodium channel encoded by SCN5A, are antiarrhythmic. We and others have shown that mutations in SCN5A cause a range of cardiac channelopathies including AF characterized by enhanced late sodium current (INa-L), prolonged AP duration and early afterdepolarizations. Genome wide association studies (GWAS) have implicated a second sodium channel Nav1.8, encoded by SCN10A, in AF susceptibility. We have identified multiple rare SCN10A variants in patients with lone AF. This raises the hypothesis, to be tested here, that rare variation in SCN10A is associated with AF. In Specific Aim 1, we will conduct a case-control genetic association study to determine whether a priori rare potentially pathogenic SCN10A variants are enriched in lone AF probands than in controls. In addition, we will ascertain extended pedigrees for each rare SCN10A variant carrier to determine familial aggregation with AF and determine genotype-phenotype correlations. Rare SCN10A variants that are highly conserved, predicted to be deleterious and aggregate with AF will be functionally characterized by expressing them in a dorsal root ganglia cell-line to determine the peak and INa-L. In vitro functional characterization of rare SCN10A variants will enable their AF-association and may provide novel insights into underlying genetic mechanisms of the arrhythmia. Furthermore, these studies also have the potential of uncovering Nav1.8 as a novel therapeutic target for antiarrhythmic intervention. In the previous cycle of this award, we used positional cloning and candidate gene approaches to identify genes encoding cardiac ion channels and signaling proteins which impart a large risk for the arrhythmia. In contrast, GWAS have identified common AF susceptibility loci with modest effects. While these approaches have provided important insights into the genetic architecture of AF, collectively they explain only a small fraction of the heritability of AF. This raises the hypothesis that rare variants with modest or large effects may be identified by whole exome sequencing (WES). In Specific Aim 2, we will screen a large cohort of patients with AF for rare variants in genes implicated by WES and GWAS as candidates for mediating AF susceptibility. We have identified four high priority novel candidate genes that cosegregated with AF using WES. Furthermore, in collaboration with other AF investigators, we have uncovered six additional AF susceptibility loci and five novel candidate genes when a meta-analysis of AF GWAS was performed. We will functionally characterize each gene variant using in vitro electrophysiology and in vivo zebrafish expression in order to determine their pathogenicity.