Andersen–Tawil syndrome type 1 (ATS1) is associated with life-threatening arrhythmias of unknown mechanism. In this study, we generated and characterized a mouse model of ATS1 carrying the trafficking-deficient mutant Kir2.1Δ314-315 channel. The mutant mouse recapitulates the electrophysiological phenotype of ATS1, with QT prolongation exacerbated by flecainide or isoproterenol, drug-induced QRS prolongation, increased vulnerability to reentrant arrhythmias and multifocal discharges resembling catecholaminergic polymorphic ventricular tachycardia (CPVT). Kir2.1Δ314-315 cardiomyocytes display significantly reduced inward rectifier K+ and Na+ currents, depolarized resting membrane potential and prolonged action potentials. We show that, in wild-type mouse cardiomyocytes and skeletal muscle cells, Kir2.1 channels localize to sarcoplasmic reticulum (SR) microdomains, contributing to intracellular Ca2+ homeostasis. Kir2.1Δ314-315 cardiomyocytes exhibit defective SR Kir2.1 localization and function, as intact and permeabilized Kir2.1Δ314-315 cardiomyocytes display abnormal spontaneous Ca2+ release events. Overall, defective Kir2.1 channel function at the sarcolemma and the SR explain the life-threatening arrhythmias in ATS1 and its overlap with CPVT.

Background: Andersen-Tawil syndrome type 1 (ATS1), caused by trafficking deficient mutations in the gene KCNJ2 coding the inward rectifier K + channel Kir2.1, is associated with life-threatening arrhythmias, which in some patients resemble catecholaminergic polymorphic ventricular tachycardia (CPVT), but the mechanisms are poorly understood. We tested the hypothesis that dysfunction of two different populations of mutant Kir2.1 channels, one at the sarcolemma, and the other at the sarcoplasmic reticulum (SR) membrane, directly alters conduction and intracellular calcium dynamics, respectively, to promote the ATS1 phenotype and arrhythmias that resemble CPVT. Methods: We generated a new mouse model of ATS1 by a single i.v. injection of cardiac specific adeno-associated viral (AAV) transduction with Kir2.1 Δ314-315 . In-vivo and cellular, structural and functional analyses of the model were carried out by electrocardiogram (ECG), magnetic resonance imaging (MRI), intracardiac stimulation, patch-clamping, membrane fractionation, western blot, immunolocalization and live calcium imaging. Results: Our mouse model carrying mutant Kir2.1 Δ314-315 recapitulated the ATS1 phenotype without modifying ventricular function. On ECG, Kir2.1 Δ314-315 mice had prolonged PR, QRS and QT intervals and occasional U waves. They showed significantly slower conduction velocities than wildtype mice in response to flecaidine-induced Na + -channel blockade, additional QT prolongation in response to isoproterenol, and increased vulnerability to cardiac fibrillation. Cardiomyocytes from Kir2.1 Δ314-315 mice had significantly reduced inward rectifier K + and Na + inward currents, depolarized resting membrane potential and prolonged action potential duration. Immunolocalization in wildtype cardiomyocytes and skeletal muscle cells revealed a novel SR microdomain of functional Kir2.1 channels contributing to intracellular Ca 2+ homeostasis. Kir2.1 Δ314-315 cardiomyocytes showed defects in SR Kir2.1 localization and function, which contributed to abnormal spontaneous Ca 2+ release events. Conclusions: Cardiac-specific AAV transduction with Kir2.1 Δ314-315 in mice recapitulates the ATS1 phenotype by disrupting localization and function of Kir2.1 channels at the SR, and the Kir2.1-Na V 1.5 channelosome at the sarcolemma. These results reveal a novel dual mechanism of arrhythmogenesis in ATS1 involving defects in Kir2.1 channel trafficking and function at two different microdomains. They also provide the first demonstration at the molecular level of the mechanism underlying the overlap between ATS1 and CPVT associated with defects in intracellular calcium homeostasis.

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on behalf of the CHARGE EKG working group Background: The QT interval, a marker of ventricular repolarization, is a heritable, independent predictor of risk for ventricular arrhythmias and sudden cardiac death (SCD). Previous genome-wide association studies (GWAS) of the QT interval have highlighted pathways regulating cardiac ion channels, calcium signaling and myocyte internal structure. However, a large proportion of the heritability remains unexplained, suggesting additional mechanisms remain undiscovered. Objective: To identify new candidate genes and pathways relevant to ventricular repolarization to elucidate novel mechanisms underlying arrhythmogenesis. Methods: We performed the largest trans-ancestry QT GWAS meta-analysis to date, using 35 studies imputed with 1000G / HRC reference panels, comprising a total sample of 252,730 individuals (84% European, 7.7% Hispanic and 6.7% African ancestry/ethnicity). Candidate gene prioritisation and gene-set enrichment analyses were performed using DEPICT.Results: We identified 176 independent loci (114 novel) associated with QT. SNP-based heritability in European ancestry UK-Biobank participants was 29.3%. The variance explained by lead and conditionally independent variants was 14.6%. Across all loci, the top 30 gene-ontology terms highlighted by DEPICT included processes involved in either muscle cell differentiation, tissue development, insulin receptor signaling or regulation of gene expression. At one locus (CD36), the association was driven by studies of African ancestry only. This gene encodes an immune-metabolic receptor necessary for appropriate myocardial substrate utilisation. Another novel locus (FAM9B) was identified in male-stratified X-chromosome analyses. Other candidate genes highlighted include cardiac Z-disk proteins (C10orf71), enzymes with cardioprotective roles in oxidative stress (PON2), cardiomyocyte glucose transporters (GLUT4) and regulators of cell morphology and cytoskeleton organization (BRWD1). Conclusion: Our analyses highlight novel genes and pathways associated with the QT interval that may