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The genetic architecture of atrial fibrillation (AF) encompasses low impact, common genetic variants and high impact, rare variants. Here, we characterize a high impact AF-susceptibility allele, KCNQ1 R231H, and describe its transcontinental geographic distribution and history. Induced pluripotent stem cell-derived cardiomyocytes procured from risk allele carriers exhibit abbreviated action potential duration, consistent with a gain-of-function effect. Using identity-by-descent (IBD) networks, we estimate the broad- and fine-scale population ancestry of risk allele carriers and their relatives. Analysis of ancestral migration routes reveals ancestors who inhabited Denmark in the 1700s, migrated to the Northeastern United States in the early 1800s, and traveled across the Midwest to arrive in Utah in the late 1800s. IBD/coalescent-based allele dating analysis reveals a relatively recent origin of the AF risk allele (~5000 years). Thus, our approach broadens the scope of study for disease susceptibility alleles to the context of human migration and ancestral origins., Many rare high-impact variants have been associated with disease, but the origins and functional impact are not always explored. Here, the authors trace the ancestry of a rare high impact atrial fibrillation allele in KCNQ1, and use iPSC-derived cardiomyocytes to characterize the effect of the allele.

Background/Aims: Congenital Sick Sinus Syndrome (SSS) is a disorder associated with sudden cardiac death due to severe bradycardia and prolonged pauses. Mutations in HCN4, the gene encoding inward Na+/K+ current (If), have been described as a cause of congenital SSS. The objective of this study is to develop an SSS model in embryonic zebrafish, and use zebrafish as a moderate-throughput assay to functionally characterize HCN4 variants. Methods: To determine the function of hcn4 in zebrafish, embryos were either bathed in the If -specific blocker (ZD-7288), or endogenous hcn4 expression was knocked down using splice-blocking morpholinos. To assess whether the zebrafish model discriminates benign from pathogenic variants, we tested four HCN4 mutations known to cause human SSS and four variants of unknown significance (VUS). Results: Pharmacological blockade and knockdown of hcn4 in zebrafish phenocopied human SSS, displaying bradycardia and cardiac pauses in intact embryos and explanted hearts. The zebrafish assay correctly identified all disease-causing variants. Of the VUS, the assay predicted 2 as benign and 2 as hypomorphic variants. Conclusions: We conclude that our embryonic zebrafish assay is a novel and effective tool to functionally characterize human HCN4 variants, which can be translated into important clinical prognostic information.

Wolff–Parkinson–White (WPW) syndrome is a common cause of supraventricular tachycardia that carries a risk of sudden cardiac death. To date, mutations in only one gene, PRKAG2, which encodes the 5’ -AMP-activated protein kinase subunit γ-2, have been identified as causative for WPW. DNA samples from five members of a family with WPW were analyzed by exome sequencing. We applied recently designed prioritization strategies (VAAST/pedigree VAAST) coupled with an ontology-based algorithm (Phevor) that reduced the number of potentially damaging variants to 10: a variant in KCNE2 previously associated with Long QT syndrome was also identified. Of these 11 variants, only MYH6 p.E1885K segregated with the WPW phenotype in all affected individuals and was absent in 10 unaffected family members. This variant was predicted to be damaging by in silico methods and is not present in the 1,000 genome and NHLBI exome sequencing project databases. Screening of a replication cohort of 47 unrelated WPW patients did not identify other likely causative variants in PRKAG2 or MYH6. MYH6 variants have been identified in patients with atrial septal defects, cardiomyopathies, and sick sinus syndrome. Our data highlight the pleiotropic nature of phenotypes associated with defects in this gene.

Background— Recent genome-wide association studies have demonstrated an association between MYH6 , the gene encoding α-myosin heavy chain (α-MHC), and sinus node function in the general population. Moreover, a rare MYH6 variant, R721W, predisposing susceptibility to sick sinus syndrome has been identified. However, the existence of disease-causing MYH6 mutations for familial sick sinus syndrome and their underlying mechanisms remain unknown. Methods and Results— We screened 9 genotype-negative probands with sick sinus syndrome families for mutations in MYH6 and identified an in-frame 3-bp deletion predicted to delete one residue (delE933) at the highly conserved coiled-coil structure within the binding motif to myosin-binding protein C in one patient. Co-immunoprecipitation analysis revealed enhanced binding of delE933 α-MHC to myosin-binding protein C. Irregular fluorescent speckles retained in the cytoplasm with substantially disrupted sarcomere striation were observed in neonatal rat cardiomyocytes transfected with α-MHC mutants carrying delE933 or R721W. In addition to the sarcomere impairments, delE933 α-MHC exhibited electrophysiological abnormalities both in vitro and in vivo. The atrial cardiomyocyte cell line HL-1 stably expressing delE933 α-MHC showed a significantly slower conduction velocity on multielectrode array than those of wild-type α-MHC or control plasmid transfected cells. Furthermore, targeted morpholino knockdown of MYH6 in zebrafish significantly reduced the heart rate, which was rescued by coexpressed wild-type human α-MHC but not by delE933 α-MHC. Conclusions— The novel MYH6 mutation delE933 causes both structural damage of the sarcomere and functional impairments on atrial action propagation. This report reinforces the relevance of MYH6 for sinus node function and identifies a novel pathophysiology underlying familial sick sinus syndrome.

Rationale: Genetic testing for Long QT Syndrome is now a standard and integral component of clinical cardiology. A major obstacle to the interpretation of genetic findings is the lack of robust functional assays to determine the pathogenicity of identified gene variants in a high-throughput manner. Objective: The goal of this study was to design and test a high-throughput in vivo cardiac assay to distinguish between disease-causing and benign KCNH2 ( hERG1) variants, using the zebrafish as a model organism. Methods and Results: We tested the ability of previously characterized Long QT Syndrome hERG1 mutations and polymorphisms to restore normal repolarization in the kcnh2 -knockdown embryonic zebrafish. The cardiac assay correctly identified a benign variant in 9 of 10 cases (negative predictive value 90%), whereas correctly identifying a disease-causing variant in 39/39 cases (positive predictive value 100%). Conclusions: The in vivo zebrafish cardiac assay approaches the accuracy of the current benchmark in vitro assay for the detection of disease-causing mutations, and is far superior in terms of throughput rate. Together with emerging algorithms for interpreting a positive long QT syndrome genetic test, the zebrafish cardiac assay provides an additional tool for the final determination of pathogenicity of gene variants identified in long QT syndrome genetic screening.

Although mortality following repair of subaortic obstruction is low, aggressive resection may increase morbidity. We sought to evaluate outcomes and risk of atrioventricular heart block (AVB) after subaortic resection in the current era. Simple obstruction was defined as a discrete subaortic membrane and complex as multilevel or diffuse narrowing. Limited resection included membranectomy and limited myomectomy. Aggressive resection included Konno, modified Konno, and Ross. Specified variables were obtained from a chart review. The 185 consecutive patients (1991-2008) ranged in age from 1 day to 21.8 years (5.1 ± 5.1 years) with 2 early and 4 late deaths. Actuarial survival was 97%, 95%, and 95% at 1, 5, and 10 years, respectively. Reoperations were required in 29 of 185 patients (15.7%); 2 required a third operation (1%). Freedom from reoperation in all patients was 97%, 83%, and 73% at 1, 5, and 10 years, respectively. Accessory mitral valve tissue ( P < .001) and age