Genetics of sudden cardiac death

An enhancer cluster controls gene activity and topology of the SCN5A-SCN10A locus in vivo

Mutations and variations in and around SCN5A, encoding the major cardiac sodium channel, influence impulse conduction and are associated with a broad spectrum of arrhythmia disorders. Here, we identify an evolutionary conserved regulatory cluster with super enhancer characteristics downstream of SCN5A, which drives localized cardiac expression and contains conduction velocity-associated variants. We use genome editing to create a series of deletions in the mouse genome and show that the enhancer cluster controls the conformation of a >0.5 Mb genomic region harboring multiple interacting gene promoters and enhancers. We find that this cluster and its individual components are selectively required for cardiac Scn5a expression, normal cardiac conduction and normal embryonic development. Our studies reveal physiological roles of an enhancer cluster in the SCN5A-SCN10A locus, show that it controls the chromatin architecture of the locus and Scn5a expression, and suggest that genetic variants affecting its activity may influence cardiac function.

Brugada syndrome & AKAP9: Reconciling clinical findings with diagnostic uncertainty

INTRODUCTION

Brugada Syndrome typically presents with sudden nocturnal arrhythmias. Diagnosis may be challenging due to variable and transient electrocardiogram patterns and nondiagnostic provocation studies. Genetic testing can establish the etiology, but results may be inconclusive with variants of uncertain significance.

CASE

A 24-year-old male with family history of sudden cardiac death was found unresponsive due to seizure. He was hemodynamically stable. ECG showed saddle-back ST elevations in V1 and V2. Procainamide challenge was negative. We subsequently performed genetic testing, which demonstrated AKAP9 variant.

DISCUSSION

AKAP9 is a scaffolding protein that facilitates phosphorylation of delayed-rectifier potassium channels. The AKAP9 variant alters potassium current causing disordered repolarization and ventricular reentry. It has been previously linked to other channelopathies, but its pathogenicity is fully undetermined.

CONCLUSION

Genetic testing is a useful tool to determine the origin of channelopathy, but inconclusive results with variants of uncertain significance should be clinically correlated.

Epidemiology of inherited arrhythmias

The primary electrical disorders are a group of inherited cardiac ventricular arrhythmias that are a major cause of sudden cardiac death in young individuals. Inherited ventricular arrhythmias result from mutations in genes encoding cardiac ion channels or their modulatory subunits. Advances in genetic screening in the past three decades have led to the assembly of large patient cohorts with these disorders. Studies in these patients, as well as in the general population, have striven to define the prevalence of these inherited arrhythmias and the characteristics of patients with different genetic subtypes of the disease. In this Review, we provide a comprehensive update on the epidemiology of inherited ventricular arrhythmias, focusing on natural history, prevalence and patient demographics. In addition, we summarize the various founder populations (groups of individuals with a disease that is caused by a genetic defect inherited from a common ancestor) that have been identified for some of these disorders and which lead to increased prevalence in some geographical regions. To date, although numerous studies have markedly increased our understanding of the epidemiology of these disorders, demographic data, especially from non-Western countries, remain scarce. Furthermore, defining the true prevalence of these disorders remains challenging. International collaboration will undoubtedly accelerate the collection of demographic information and improve the accuracy of prevalence data.

Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes as Models for Cardiac Channelopathies: A Primer for Non-Electrophysiologists

Life threatening ventricular arrhythmias leading to sudden cardiac death are a major cause of morbidity and mortality. In the absence of structural heart disease, these arrhythmias, especially in the younger population, are often an outcome of genetic defects in specialized membrane proteins called ion channels. In the heart, exceptionally well-orchestrated activity of a diversity of ion channels mediates the cardiac action potential. Alterations in either the function or expression of these channels can disrupt the configuration of the action potential, leading to abnormal electrical activity of the heart that can sometimes initiate an arrhythmia. Understanding the pathophysiology of inherited arrhythmias can be challenging because of the complexity of the disorder and lack of appropriate cellular and in vivo models. Recent advances in human induced pluripotent stem cell technology have provided remarkable progress in comprehending the underlying mechanisms of ion channel disorders or channelopathies by modeling these complex arrhythmia syndromes in vitro in a dish. To fully realize the potential of induced pluripotent stem cells in elucidating the mechanistic basis and complex pathophysiology of channelopathies, it is crucial to have a basic knowledge of cardiac myocyte electrophysiology. In this review, we will discuss the role of the various ion channels in cardiac electrophysiology and the molecular and cellular mechanisms of arrhythmias, highlighting the promise of human induced pluripotent stem cell-cardiomyocytes as a model for investigating inherited arrhythmia syndromes and testing antiarrhythmic strategies. Overall, this review aims to provide a basic understanding of the electrical activity of the heart and related channelopathies, especially to clinicians or research scientists in the cardiovascular field with limited electrophysiology background.

Pharmacological Modulation of Right Ventricular Endocardial-Epicardial Gradients in Brugada Syndrome

Background We explored the hypothesis that increased cholinergic tone exerts its proarrhythmic effects in Brugada syndrome (BrS) through increasing dispersion of transmural repolarization in patients with spontaneous and drug-induced BrS. Methods BrS and supraventricular tachycardia patients were studied after deploying an Ensite Array in the right ventricular outflow tract and a Cardima catheter in the great cardiac vein to record endo and epicardial signals, respectively. S₁-S₂ restitution curves from the right ventricular apex were conducted at baseline and after edrophonium challenge to promote increased cholinergic tone. The local unipolar electrograms were then analyzed to study transmural conduction and repolarization dynamics. Results The study included 8 BrS patients (5 men:3 women; mean age, 56 years) and 8 controls patients with supraventricular tachycardia (5 men:3 women; mean age, 48 years). Electrophysiological studies in controls demonstrated shorter endocardial than epicardial right ventricular activation times (mean difference: 26 ms; P<0.001). In contrast, patients with BrS showed longer endocardial than epicardial activation time (mean difference: -15 ms; P=0.001). BrS hearts, compared with controls, showed significantly larger transmural gradients in their activation recovery intervals (mean intervals, 20.5 versus 3.5 ms; P<0.01), with longer endocardial than epicardial activation recovery intervals. Edrophonium challenge increased such gradients in both controls (to a mean of 16 ms [ P<0.001]) and BrS (to 29.7 ms; P<0.001). However, these were attributable to epicardial and endocardial activation recovery interval prolongations in control and BrS hearts, respectively. Dynamic changes in repolarization gradients were also observed across the BrS right ventricular wall in BrS. Conclusions Differential contributions of conduction and repolarization were identified in BrS which critically modulated transmural dispersion of repolarization with significant cholinergic effects only identified in the patients with BrS. This has important implications for explaining the proarrhythmic effects of increased vagal tone in BrS, as well as evaluating autonomic modulation and epicardial ablation as therapeutic strategies.

Utilization of the genome aggregation database, in silico tools, and heterologous expression patch-clamp studies to identify and demote previously published type 2 long QT syndrome: Causative variants from pathogenic to likely benign

BACKGROUND

Loss-of-function variants in the KCNH2-encoded Kv11.1 potassium channel cause long QT syndrome (LQTS) type 2 (LQT2). Presently, hundreds of KCNH2 missense variants (MVs) have been published as "disease-causative." However, an estimated 10% of rare published LQTS MVs may be "false positives."

OBJECTIVE

The purpose of this study was to determine which published KCNH2 MVs are likely false positives and warrant demotion to "likely benign" status.

METHODS

A list of 337 LQT2-associated MVs from 6 large compendia was compiled. MV frequency within the Genome Aggregation Database (gnomAD) (n = 141,352 individuals) was assessed, and MVs were analyzed with 8 in silico tools. Variants with minor allele frequency (MAF) >7*10E-6, the calculated maximum credible frequency of LQT2, and predicted "benign" by all tools were demoted to "likely benign." Ultra-rare variants (n = 8) absent in gnomAD but predicted "benign" by all tools were considered as potential false positives and were characterized functionally using whole-cell patch clamp.

RESULTS

Overall, 14 of 337 published KCNH2 MVs (4%) were observed at MAF >7*10E-6, whereas 252 of 337 (75%) were absent in gnomAD. Among the latter, 8 variants (I96V, G187S, A203T, P241L, H254Q, G314S, P935S, P963T) were predicted benign by 8 tools and lacked characterization. Patch clamp showed no functional perturbation for these 8 MVs.

CONCLUSION

This study offers compelling evidence for the demotion of 22 of 337 KCNH2 variants (6.5%) in the literature. Meticulous "pruning" of compendia using exome/genome databases, in silico tools, and in vitro functional studies must be conducted not only for putatively pathogenic LQTS MVs but for the entire field of genetic heart disease.

Sudden Cardiac Death: Who Is at Risk?

Sudden cardiac death (SCD) is a leading cause of death in the United States. Despite improvements in therapy, the incidence of SCD as a proportion of overall cardiovascular death remains relatively unchanged. This article aims to answer the question, "Who is at risk for SCD?" In the process, it reviews the definition, pathophysiology, epidemiology, and risk factors of SCD. Patients at risk for SCD and appropriate treatment strategies are discussed.

Beyond the One Gene-One Disease Paradigm: Complex Genetics and Pleiotropy in Inheritable Cardiac Disorders

Inheritable cardiac disorders, which may be associated with cardiomyopathic changes, are often associated with increased risk of sudden death in the young. Early linkage analysis studies in Mendelian forms of these diseases, such as hypertrophic cardiomyopathy and long-QT syndrome, uncovered large-effect genetic variants that contribute to the phenotype. In more recent years, through genotype-phenotype studies and methodological advances in genetics, it has become evident that most inheritable cardiac disorders are not monogenic but, rather, have a complex genetic basis wherein multiple genetic variants contribute (oligogenic or polygenic inheritance). Conversely, studies on genes underlying these disorders uncovered pleiotropic effects, with a single gene affecting multiple and apparently unrelated phenotypes. In this review, we explore these 2 phenomena: on the one hand, the evidence that variants in multiple genes converge to generate one clinical phenotype, and, on the other, the evidence that variants in one gene can lead to apparently unrelated phenotypes. Although multiple conditions are addressed to illustrate these concepts, the experience obtained in the study of long-QT syndrome, Brugada syndrome, and arrhythmogenic cardiomyopathy, and in the study of functions related to SCN5A (the gene coding for the α-subunit of the most abundant sodium channel in the heart) and PKP2 (the gene coding for the desmosomal protein plakophilin-2), as well, is discussed in more detail.

Whole genome and transcriptome sequencing of post-mortem cardiac tissues from sudden cardiac death victims identifies a gene regulatory variant in NEXN

BACKGROUND

Sudden cardiac death (SCD) is a major public health problem and constitutes a diagnostic and preventive challenge in forensic pathology, especially for cases with structural normal hearts at autopsy, so-called sudden arrhythmic death syndrome (SADS). The identification of new genetic risk factors that predispose to SADS is important, because they may contribute to establish the diagnosis and increase the understanding of disease pathways underlying SADS. Pathogenic mutations in the protein coding regions of cardiac genes were found in relation to SADS. However, much remains unknown about variants in non-coding regions of the genome.

METHODS AND RESULTS

In this study, we explored the potential of whole genome sequencing (WGS) and whole transcriptome sequencing (WTS) to find DNA variants in SCD victims with structural normal hearts. With focus on the non-coding regulatory regions, we re-examined a cohort of 13 SADS and sudden unexplained death in infancy (SUDI) victims without disease causing DNA variants in recognized cardiac genes. The genetic re-examination of DNA was carried out using frozen tissue samples and WTS was carried out using five distinct formalin fixed and paraffin embedded (FFPE) cardiac tissue samples from each individual, including anterior and posterior walls of the left ventricle, ventricular papillary muscle, septum, and the right ventricle. We identified 23 candidate variants in regulatory sequences of cardiac genes, including a variant in the promotor region of NEXN, c.-194A>G, that was found to be statistically significantly (p < 0.05) associated with decreased expression of NEXN and cardiac hypertrophy.

CONCLUSION

With the use of post-mortem FFPE tissues, we highlight the potential of using WTS investigations and compare gene expression levels with DNA variation in regulatory non-coding regions of the genome for a better understanding of the genetics of cardiac diseases leading to SCD.

Autonomic modulation of the electrical substrate in mice haploinsufficient for cardiac sodium channels: a model of the Brugada syndrome

A murine line haploinsufficient in the cardiac sodium channel has been used to model human Brugada syndrome: a disease causing sudden cardiac death due to lethal ventricular arrhythmias. We explored the effects of cholinergic tone on electrophysiological parameters in wild-type and genetically modified, heterozygous, Scn5a+/- knockout mice. Scn5a+/- ventricular slices showed longer refractory periods than wild-type both at baseline and during isoprenaline challenge. Scn5a+/- hearts also showed lower conduction velocities and increased mean increase in delay than did littermate controls at baseline and blunted responses to isoprenaline challenge. Carbachol exerted limited effects but reversed the effects of isoprenaline with coapplication. Scn5a+/- mice showed a reduction in conduction reserve in that isoprenaline no longer increased conduction velocity, and this was not antagonized by muscarinic agonists.

Sudden unexpected cardiac death and postmortem identification of a novel RYR2 gene mutation

A 13-year-old female was found lifeless at home. The autopsy and consecutive histological and toxicological examinations showed blood-rich and edematous lungs and foamy bloody content in the airways. No morphologic pathological findings were seen, especially no bleeding sources. Toxicological findings were unremarkable. The specific cause of death remained unclear. Due to reported losses of consciousness, a moleculargenetic postmortem testing was performed. A so far undescribed mutation in the cardiac ryanodine receptor gene RyR2 was detected. This mutation is suitable to explain the case history as well as the morphological findings. The cardiac ryanodine receptor gene RyR2 encodes the ryanodine receptor type 2, an ion channel in the cardiomyocytes. The ion channel regulates the influx of calcium ions and thus influences myocardial activity. Mutations in this channel may result in the catecholaminergic polymorphic ventricular tachycardia (CPVT), a cardiac arrhythmia that can lead to syncope and sudden cardiac death. This case demonstrates the usefulness and need of molecular autopsy, in particular to identify and treat possibly affected family members.

Gene Therapy for Catecholaminergic Polymorphic Ventricular Tachycardia by Inhibition of Ca2+/Calmodulin-Dependent Kinase II

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT), an inherited cardiac arrhythmia characterized by adrenergically triggered arrhythmias, is inadequately treated by current standard of care. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), an adrenergically activated kinase that contributes to arrhythmogenesis in heart disease models, is a candidate therapeutic target in CPVT. However, translation of CaMKII inhibition has been limited by the need for selective CaMKII inhibition in cardiomyocytes. Here, we tested the hypothesis that CaMKII inhibition with a cardiomyocyte-targeted gene therapy strategy would suppress arrhythmia in CPVT mouse models.

METHODS

We developed AAV9-GFP-AIP, an adeno-associated viral vector in which a potent CaMKII inhibitory peptide, autocamtide-2-related inhibitory peptide [AIP], is fused to green fluorescent protein (GFP) and expressed from a cardiomyocyte selective promoter. The vector was delivered systemically. Arrhythmia burden was evaluated with invasive electrophysiology testing in adult mice. AIP was also tested on induced pluripotent stem cells derived from patients with CPVT with different disease-causing mutations to determine the effectiveness of our proposed therapy on human induced pluripotent stem cell-derived cardiomyocytes and different pathogenic genotypes.

RESULTS

AAV9-GFP-AIP was robustly expressed in the heart without significant expression in extracardiac tissues, including the brain. Administration of AAV9-GFP-AIP to neonatal mice with a known CPVT mutation (RYR2^R176Q/+) effectively suppressed ventricular arrhythmias induced by either β-adrenergic stimulation or programmed ventricular pacing, without significant proarrhythmic effect. Intravascular delivery of AAV9-GFP-AIP to adolescent mice transduced ≈50% of cardiomyocytes and was effective in suppressing arrhythmia in CPVT mice. Induced pluripotent stem cell-derived cardiomyocytes derived from 2 different patients with CPVT with different pathogenic mutations demonstrated increased frequency of abnormal calcium release events, which was suppressed by a cell-permeable form of AIP.

CONCLUSIONS

This proof-of-concept study showed that AAV-mediated delivery of a CaMKII peptide inhibitor to the heart was effective in suppressing arrhythmias in a murine model of CPVT. CaMKII inhibition also reversed the arrhythmia phenotype in human CPVT induced pluripotent stem cell-derived cardiomyocyte models with different pathogenic mutations.

Genotype/Phenotype Relationship in a Consanguineal Family With Brugada Syndrome Harboring the R1632C Missense Variant in the SCN5A Gene

Brugada syndrome (BrS) is a known cause of sudden cardiac death. The genetic basis of BrS is not well understood, and no one single gene is linked to even a majority of BrS cases. However, mutations in the gene SCN5A are the most common, although the high amount of phenotypic variability prevents a clear correlation between genotype and phenotype. Research techniques are limited, as most BrS cases still remain without a genetic diagnosis, thus impairing the implementation of experimental models representative of a general pathogenetic mechanism. In the present study, we report the largest family to-date with the segregation of the heterozygous variant NM_198056:c.4894C>T (p.Arg1632Cys) in the SCN5A gene. The genotype-phenotype relationship observed suggests a likely pathogenic effect of this variant. Functional studies to better understand the molecular effects of this variant are warranted.

Genetic risk stratification in cardiac arrhythmias

PURPOSE OF REVIEW

The current article provides a concise summary of the possibilities and limitations of genotype-based risk stratification of cardiac arrhythmias. We will outline the most important findings of the recent years in the light of their chronological and conceptual development.

RECENT FINDINGS

Genotype-phenotype association studies in families with single-gene disorders as well as in the general population led to the discovery of several DNA variants significantly associated with the risk of sudden death or life-threatening arrhythmias. In genetic (monogenic) diseases, the disease-causing mutations modulate the risk of events and response to antiarrhythmic therapy according to the specific gene involved, to their position of the mutation and to their functional effects. These causal relationships have been quite well characterized in the case of long QT syndrome but are still less defined in the case of other inherited conditions. Quantitatively, the risk associated with a single genetic variant is large for DNA variants that cause monogenic inherited arrhythmias. Much different is the case of more common variants associated with the risk of arrhythmias in the general population as they are generally associated with a small effect size.

SUMMARY

Genetic profiling identifies arrhythmogenic risk even if a complete picture allowing high-granularity risk stratification is yet to come.

The Atrial Phenotype of the Inherited Primary Arrhythmia Syndromes

Over the past two decades, our understanding of inherited primary arrhythmia syndromes has been enriched by studies that have aimed to define the clinical characteristics and the genetic, cellular and molecular features predisposing patients to an enhanced risk of ventricular arrhythmias. In contrast, very little is known about the causative role of inherited cardiac channelopathies on atrial conduction abnormalities possibly leading to different atrial tachyarrhythmias. The diagnostic and therapeutic management of patients with an inherited cardiac channelopathy presenting with atrial arrhythmias remains highly challenging and is in urgent need of improvement. This review will assess the current knowledge on atrial electrical abnormalities affecting patients with different forms of inherited primary arrhythmia syndromes, including long and short QT syndromes, early repolarisation syndrome, catecholaminergic polymorphic ventricular tachycardia and Brugada syndrome.

Recent understanding of clinical sequencing and gene-based risk stratification in inherited primary arrhythmia syndrome

Inherited primary arrhythmia syndromes (IPAS) may result in ventricular tachycardia or ventricular fibrillation by some genetic disorders, leading to sudden cardiac death. IPAS are also called "channelopathies" since many of these are caused by an abnormality in myocardial ion channels. Congenital long-QT syndrome (LQTS) is the most well documented IPAS, which may be seen in 0.1% of the general population. More than 15 disease-causing genes have been identified in almost 70% of LQTS patients and genetic testing is well applied to not only clinical diagnosis but also risk stratification and gene-based therapeutic strategy for each person with LQTS. Thus, in LQTS, gene-based personalized medicine can be realized. Unlike the LQTS, genetic testing for the Brugada syndrome (BrS) is still controversial since only 20% of patients can be identified with the causing gene mutations, most of which are in SCN5A. Furthermore, even in the SCN5A mutation-positive carriers, their phenotypes are not completely consistent with BrS, but may cause other IPAS including LQTS, cardiac conduction defect, sick sinus syndrome, and dilated cardiomyopathy. On the other hand, a recent Japanese BrS registry demonstrated that the pore-region mutations in SCN5A are significantly associated with a risk of lethal cardiac events. Furthermore, a genome-wide association study revealed that a common variant in SCN10A or HEY2 in addition to SCN5A is associated with BrS, thus, BrS may not be a monogenic Mendelian disease but probably an oligogenic disease. The purpose of this review is to describe the basic genetic and pathophysiological findings of the IPAS, particularly LQTS and Brugada syndrome, and to outline a rational approach to genetic testing, management, and family screening.

Whole-Exome Sequencing Identifies a Novel Mutation (p.L320R) of Alpha-Actinin 2 in a Chinese Family with Dilated Cardiomyopathy and Ventricular Tachycardia

Dilated cardiomyopathy (DCM) is a severe cardiovascular disease which can lead to heart failure and sudden cardiac death (SCD). The typical feature of DCM is left ventricular enlargement or dilatation. In some conditions, DCM and arrhythmia can occur concurrently, apparently promoting the prevalence of SCD. According to previous studies, mutations in more than 100 genes have been detected in DCM and/or arrhythmia patients. Here, we report a Chinese family with typical DCM, ventricular tachycardia, syncope, and SCD. Using whole-exome sequencing, a novel, likely pathogenic mutation (c.959T>G/p.L320R) of actinin alpha 2 (ACTN2) was identified in all affected family members. This novel mutation was also predicted to be disease-causing by MutationTaster, SIFT, and Polyphen-2. Our study not only expands the spectrum of ACTN2 mutations and contributes to the genetic diagnosis and counseling of the family, but also provides a new case with overlap phenotype that may be caused by the ACTN2 variant.

Implantable Cardioverter-Defibrillators are the Main Link in the Modern Concept of Sudden Cardiac Death Prevention. Problems and Prospects of the Development of the Method

The article covers the development of the problem of sudden cardiac death prevention with the implantable cardioverter-defibrillators from the moment of creation of these devices to our days. The current concept of primary prevention of sudden cardiac death, based on the severity of manifestation of heart failure and left ventricular dysfunction, is not effective enough. Its practical application is difficult because it requires mass application of implantable defibrillators, with low predictive accuracy of these criteria in terms of development of life-threatening arrhythmias. The development of methods for visualizing the myocardium, allowing to assess the severity of myocardial fibrosis, as well as the possibilities of medical genetics, at the present stage, allows us to clarify indications for implantation of cardioverter-defibrillators and thereby significantly improve the concept of preventing sudden cardiac death with these instruments.

The Cardiac Gap Junction has Discrete Functions in Electrotonic and Ephaptic Coupling

Connexin43-formed gap junctions have long been thought to contribute to cardiac conduction in the mammalian ventricle by providing direct electrotonic connectivity between the cytoplasms of neighboring cardiomyocytes. However, accumulating data from studies of non-mammalian hearts, Connexin 43 (Cx43) knockout mice and human Cx43 mutations have raised questions as to whether gap junctions are the sole means by which electrical coupling between cardiomyocytes is accomplished. Computational and experimental work over the last decade have indicated that intercellular propagation of action potentials in the heart may involve both electrotonic and ephaptic contributions-in what has been dubbed "mixed-mode" conduction. Interestingly, the Cx43 gap junction may provide a common structural platform in mammals that facilitates the operation of these two mechanisms. In addition to gap junction channels functioning in an electrotonic role, the perinexus region at the edge of gap junctions may be provide a niche for voltage-gated sodium channels from neighboring cells to be in sufficiently close proximity to enable ephaptic transmission of action potential. A novel role has recently been identified in this potential ephaptic mechanism for inter-membrane adhesion mediated by the beta subunit (beta1/Scn1b) of the sodium channel. The new perspective of the operational redundancy that is built into cardiac electrical connectivity could provide new understanding of arrhythmia mechanisms and holds the promise for new approach to anti-arrhythmic therapy. Anat Rec, 302:93-100, 2019. © 2018 Wiley Periodicals, Inc.

Whole-exome sequencing reveals doubly novel heterozygous Myosin Binding Protein C and Titin mutations in a Chinese patient with severe dilated cardiomyopathy

BACKGROUND

Dilated Cardiomyopathy is a serious heart disorder that may induce sudden cardiac death and heart failure. Significant progress has been made in understanding the molecular basis of dilated cardiomyopathy. In previous studies, mutations in more than fifty genes have been identified in dilated cardiomyopathy patients. The purpose of this study was to detect the genetic lesion in a family from the central south of China affected by severe dilated cardiomyopathy.

METHODS

Whole-exome sequencing combined with cardiomyopathy-related genes list were used to analyse the mutations of the proband. Co-segregation analysis was performed by Sanger sequencing.Results and conclusionsTwo novel heterozygous mutations - Myosin Binding Protein C: p.L1014RfsX6 and Titin: p.R9793X - were identified in the proband. The deletion mutation c.3041delT/p.L1014RfsX6 caused a premature stop codon at position 1020 in exon 28 of the Myosin Binding Protein C. The nonsense mutation, c.29377 C>T/ p. R9793X, of Titin was located in the highly evolutionarily conserved domain, resulting in truncation of the Titin protein as well. Co-segregation analysis further revealed that the Myosin Binding Protein C mutation came from his mother and the Titin mutation came from his father. Both mutations are reported in dilated cardiomyopathy patients for the first time. Our study not only provides a unique example of the genes and molecular mechanisms involved in dilated cardiomyopathy but also expands the spectrum of Myosin Binding Protein C and Titin mutations and contributes to the genetic diagnosis and counselling of dilated cardiomyopathy patients.

Modifier genes for sudden cardiac death

Genetic conditions, even those associated with identical gene mutations, can present with variable clinical manifestations. One widely accepted explanation for this phenomenon is the existence of genetic factors capable of modifying the consequences of disease-causing mutations (modifier genes). Here, we address the concepts and principles by which genetic factors may be involved in modifying risk for cardiac arrhythmia, then discuss the current knowledge and interpretation of their contribution to clinical heterogeneity. We illustrate these concepts in the context of two important clinical conditions associated with risk for sudden cardiac death including a monogenic disorder (congenital long QT syndrome) in which the impact of modifier genes has been established, and a complex trait (life-threatening arrhythmias in acute myocardial infarction) for which the search for genetic modifiers of arrhythmic risk is more challenging. Advances in understanding the contribution of modifier genes to a higher or lower propensity towards sudden death should improve patient-specific risk stratification and be a major step towards precision medicine.

Risk Stratification of Sudden Cardiac Death in Patients with Heart Failure: An update

Heart failure (HF) is a complex clinical syndrome in which structural/functional myocardial abnormalities result in symptoms and signs of hypoperfusion and/or pulmonary or systemic congestion at rest or during exercise. More than 80% of deaths in patients with HF recognize a cardiovascular cause, with most being either sudden cardiac death (SCD) or death caused by progressive pump failure. Risk stratification of SCD in patients with HF and preserved (HFpEF) or reduced ejection fraction (HFrEF) represents a clinical challenge. This review will give an update of current strategies for SCD risk stratification in both HFrEF and HFpEF.

Sudden unexpected death in the young - Value of massive parallel sequencing in postmortem genetic analyses

Cases of sudden cardiac death (SCD) in young and apparently healthy individuals represent a devastating event in affected families. Hereditary arrhythmia syndromes, which include primary electrical heart disorders as well as cardiomyopathies, are known to contribute to a significant number of these sudden death cases. We performed postmortem genetic analyses in young sudden death cases (aged <45years) by means of a defined gene panel using massive parallel sequencing (MPS). The data were evaluated bioinformatically and detected sequence variants were assessed using common databases and applying in silico prediction tools. In this study, we identified variants with likely pathogenic effect in 6 of 9 sudden unexpected death (SUD) cases. Due to the detection of numerous unknown and unclassified variants, interpretation of the results proved to be challenging. However, by means of an appropriate evaluation of the findings, MPS represents an important tool to support the forensic investigation and implies great progress for relatives of young SCD victims facilitating adequate risk stratification and genetic counseling.

An African loss-of-function CACNA1C variant p.T1787M associated with a risk of ventricular fibrillation

Calcium regulation plays a central role in cardiac function. Several variants in the calcium channel Ca_v1.2 have been implicated in arrhythmic syndromes. We screened patients with Brugada syndrome, short QT syndrome, early repolarisation syndrome, and idiopathic ventricular fibrillation to determine the frequency and pathogenicity of Ca_v1.2 variants. Ca_v1.2 related genes, CACNA1C, CACNB2 and CACNA2D1, were screened in 65 probands. Missense variants were introduced in the Ca_v1.2 alpha subunit plasmid by mutagenesis to assess their pathogenicity using patch clamp approaches. Six missense variants were identified in CACNA1C in five individuals. Five of them, A1648T, A1689T, G1795R, R1973Q, C1992F, showed no major alterations of the channel function. The sixth C-terminal variant, Ca_vα_1c-T1787M, present mostly in the African population, was identified in two patients with resuscitated cardiac arrest. The first patient originated from Cameroon and the second was an inhabitant of La Reunion Island with idiopathic ventricular fibrillation originating from Purkinje tissues. Patch-clamp analysis revealed that Ca_vα_1c-T1787M reduces the calcium and barium currents by increasing the auto-inhibition mediated by the C-terminal part and increases the voltage-dependent inhibition. We identified a loss-of-function variant, Ca_vα_1c-T1787M, present in 0.8% of the African population, as a new risk factor for ventricular arrhythmia.

Telomere length measurement as a clinical biomarker of aging and disease

Telomere length measurement is increasingly recognized as a clinical gauge for age-related disease risk. There are several methods for studying blood telomere length (BTL) as a clinical biomarker. The first is an observational study approach, which directly measures telomere lengths using either cross-sectional or longitudinal patient cohorts and compares them to a population of age- and sex-matched individuals. These direct traceable measurements can be considered reflective of an individual's current health or disease state. Escalating interest in personalized medicine, access to high-throughput genotyping and resulting acquisition of large volumes of genetic data corroborates the second method, Mendelian randomization (MR). MR employs telomere length-associated genetic variants to indicate predisposition to disease risk based on the genomic composition of the individual. When assessed from cells in the bloodstream, telomeres can show variation from their genetically predisposed lengths due to environmental-induced changes. These alterations in telomere length act as an indicator of cellular health, which, in turn, can provide disease risk status. Overall, BTL measurement is a dynamic marker of biological health and well-being that together with genetically defined telomere lengths can provide insights into improved healthcare for the individual.

Associations between common ion channel single nucleotide polymorphisms and sudden cardiac death in adults: A MOOSE-compliant meta-analysis

BACKGROUND

We sought to identify common ion channel single nucleotide polymorphisms (SNPs) associated with the occurrence of sudden cardiac death (SCD) to predict the incidence of SCD in clinical settings.

METHODS

This study involved a systematic review and meta-analysis of ion channel SNPs and risk of SCD in adults. We searched public databases for studies published up to September 19, 2017. We examined relationships between SNPs in common ion channel genes and the incidence of SCD.

RESULTS

We collected data for 22 trials that included a total of 4149 patients who experienced SCD or had a high risk of SCD and assessed these data in our meta-analysis. An allelic model showed that rs11720524 in SCN5A clearly protected against SCD (odds ratio [OR]: 0.76; 95% confidence interval [95% CI]: 0.67-0.85; P < .001). Subgroup analysis showed that rs11720524 in SCN5A protected against SCD in Europeans and Caucasians but not in Koreans. The allelic model indicated that rs12296050 in KCNQ1 also had significant protective effects against SCD (OR: 0.85; 95% CI: 0.76-0.96; P = .007). Moreover, this model demonstrated that rs2283222 in KCNQ1 had a significant negative relationship with SCD (OR: 0.73; 95% CI: 0.62-0.85; P < .001). Rs12296050 in KCNQ1 protected against SCD in Koreans and Americans. Our results also showed that rs790896 in RYR2 was negatively associated with SCD in a dominant model (OR: 0.66; 95% CI: 0.45-0.97; P = .033).

CONCLUSIONS

Rs11720524 in SCN5A is negatively related to SCD in Europeans and Caucasians, and rs12296050 and rs2283222 in KCNQ1 and rs790896 in RYR2 clearly have protective effects against SCD.

Role of ion channels in heart failure and channelopathies

Heart failure (HF) is a complication of multiple cardiac diseases and is characterized by impaired contractile and electric function. Patients with HF are not only limited by reduced contractile function but are also prone to life-threatening ventricular arrhythmias. HF itself leads to remodeling of ion channels, gap junctions, and intracellular calcium handling abnormalities that in combination with structural remodeling, e.g., fibrosis, produce a substrate for an arrhythmogenic disorders. Not only ventricular life-threatening arrhythmias contribute to increased morbidity and mortality but also atrial arrhythmias, especially atrial fibrillation (AF), are common in HF patients and contribute to morbidity and mortality. The distinct ion channel remodeling processes in HF and in channelopathies associated with HF will be discussed. Further basic research and clinical studies are needed to identify underlying molecular pathways of HF pathophysiology to provide the basis for improved patient care and individualized therapy based on individualized ion channel composition and remodeling.

Human iPSC-Derived Cardiomyocytes for Investigation of Disease Mechanisms and Therapeutic Strategies in Inherited Arrhythmia Syndromes: Strengths and Limitations

During the last two decades, significant progress has been made in the identification of genetic defects underlying inherited arrhythmia syndromes, which has provided some clinical benefit through elucidation of gene-specific arrhythmia triggers and treatment. However, for most arrhythmia syndromes, clinical management is hindered by insufficient knowledge of the functional consequences of the mutation in question, the pro-arrhythmic mechanisms involved, and hence the most optimal treatment strategy. Moreover, disease expressivity and sensitivity to therapeutic interventions often varies between mutations and/or patients, underlining the need for more individualized strategies. The development of the induced pluripotent stem cell (iPSC) technology now provides the opportunity for generating iPSC-derived cardiomyocytes (CMs) from human material (hiPSC-CMs), enabling patient- and/or mutation-specific investigations. These hiPSC-CMs may furthermore be employed for identification and assessment of novel therapeutic strategies for arrhythmia syndromes. However, due to their relative immaturity, hiPSC-CMs also display a number of essential differences as compared to adult human CMs, and hence there are certain limitations in their use. We here review the electrophysiological characteristics of hiPSC-CMs, their use for investigating inherited arrhythmia syndromes, and their applicability for identification and assessment of (novel) anti-arrhythmic treatment strategies.

A novel mutation of dipeptidyl aminopeptidase-like protein-6 in a family with suspicious idiopathic ventricular fibrillation

BACKGROUND

Sudden cardiac death (SCD) occurs in a broad spectrum of cardiac pathologies and is an important cause of mortality in the general population. Idiopathic ventricular fibrillation (IVF) is a rare but important factor resulting in SCD. It is diagnosed in a resuscitated cardiac arrest victim underlying unknown cause, with documented ventricular fibrillation. Previous studies have demonstrated that mutations in dipeptidyl aminopeptidase-like protein-6 (DPP6) and cardiac sodium channel Nav1.5 (SCN5A) are the most important genetic factors involve in IVF.

AIM

By using whole sequencing to identify the genetic lesion of a family with suspicious idiopathic ventricular fibrillation.

DESIGN

Prospective genetic study.

METHODS

In this study, we employed whole-exome sequencing in combination with arrhythmia-related gene filtering to identify the genetic lesion for a family suffering from suspicious IVF, syncope and SCD. We then generated the plasmids of DPP6-pcDNA3.1+ (WT and c.1578G>C/p.Q526H). Kv4.3-pcDNA3.1+ was co-transfected together with/without DPP6-pcDNA3.1+ (WT and/or c.1578G>C/p.Q526H) into HEK293 cells to perform the patch clamp experiments.

RESULTS

A novel missense mutation (c.1578G>C/p.Q526H) of DPP6 was identified and co-segregated with affected patients in this family. Patch clamp experiments suggested that this novel mutation might result in a gain of function and disturb the efflux of potassium ion.

CONCLUSION

Our study not only reported the second missense mutation of DPP6 in heart disease and expanded the spectrum of DPP6 mutations, but also contribute to the genetic diagnosis and counseling of families with suspicious IVF, syncope and SCD.

Selective late sodium current inhibitor GS-458967 suppresses Torsades de Pointes by mostly affecting perpetuation but not initiation of the arrhythmia

Background and Purpose

Enhanced late sodium current (late I_Na) in heart failure and long QT syndrome type 3 is proarrhythmic. This study investigated the antiarrhythmic effect and mode of action of the selective and potent late I_Na inhibitor GS‐458967 (GS967) against Torsades de Pointes arrhythmias (TdP) in the chronic atrioventricular block (CAVB) dog.

Experimental Approach

Electrophysiological and antiarrhythmic effects of GS967 were evaluated in isolated canine ventricular cardiomyocytes and CAVB dogs with dofetilide‐induced early afterdepolarizations (EADs) and TdP, respectively. Mapping of intramural cardiac electrical activity in vivo was conducted to study effects of GS967 on spatial dispersion of repolarization.

Key Results

GS967 (IC₅₀~200nM) significantly shortened repolarization in canine ventricular cardiomyocytes and sinus rhythm (SR) dogs, in a concentration and dose‐dependent manner. In vitro, despite addition of 1μM GS967, dofetilide‐induced EADs remained present in 42% and 35% of cardiomyocytes from SR and CAVB dogs, respectively. Nonetheless, GS967 (787±265nM) completely abolished dofetilide‐induced TdP in CAVB dogs (10/14 after dofetilide to 0/14 dogs after GS967), while single ectopic beats (sEB) persisted in 9 animals. In vivo mapping experiments showed that GS967 significantly reduced spatial dispersion of repolarization: cubic dispersion was significantly decreased from 237±54ms after dofetilide to 123±34ms after GS967.

Conclusion and Implications

GS967 terminated all dofetilide‐induced TdP without completely suppressing EADs and sEB in vitro and in vivo, respectively. The antiarrhythmic mode of action of GS967, through the reduction of spatial dispersion of repolarization, seems to predominantly impede the perpetuation of arrhythmic events into TdP rather than their initiating trigger.

Serum lipid feature and potential biomarkers of lethal ventricular tachyarrhythmia (LVTA) induced by myocardial ion channel diseases: a rat model study

To determine the cause of death in myocardial ion channel diseases (MICD)-induced sudden cardiac death (SCD) cases is a difficulty in forensic identification practices. The majority of MICD-induced SCD cases would experience lethal ventricular tachyarrhythmia (LVTA) before deaths; thus, confirming the occurrence of LVTA in bodies can offer a key evidence to identify these cases. Several lipids in the myocardia were found disturbed after LVTA; yet, whether serum lipidome would be disrupted by LVTA is not clear. Therefore, we aimed to screen lipid feature and related diagnostic markers of LVTA in serum here. An aconitine-induced LVTA-SCD rat model was produced. Blood samples before LVTA and immediately after LVTA were retrieved and related serum specimens were used for ultra-performance liquid chromatography-mass spectrometry (UPLC-MS)-based lipidomics analyses. On the basis of the defined differential lipids, a lipid-related metabolic pathway network was constructed and potential biomarkers were screened. Twelve aconitine-induced LVTA rats were produced. Totally, 188 lipids in serum were disrupted during the LVTA-SCD process, which belong to 11 lipid classes. Most of the differential lipids were correlated, suggesting that they were interacted and that the changes were holistic during LVTA process. Ten lipid pathways were activated during LVTA process; the main lipid classes involved in these pathways were ceramide, sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine. Phosphatidylcholine O-40:4, sphingomyelin d46:5, and phosphatidylethanolamine 40:4 were tested as potential diagnostic markers of LVTA-SCD event in serum. The current results indicate a substantial change in serum lipidome after LVTA-SCD; lipidomics holds promise to identify MICD-induced SCDs in forensic practices.

Ion Channel Disorders and Sudden Cardiac Death

Long QT syndrome, short QT syndrome, Brugada syndrome and catecholaminergic polymorphic ventricular tachycardia are inherited primary electrical disorders that predispose to sudden cardiac death in the absence of structural heart disease. Also known as cardiac channelopathies, primary electrical disorders respond to mutations in genes encoding cardiac ion channels and/or their regulatory proteins, which result in modifications in the cardiac action potential or in the intracellular calcium handling that lead to electrical instability and life-threatening ventricular arrhythmias. These disorders may have low penetrance and expressivity, making clinical diagnosis often challenging. However, because sudden cardiac death might be the first presenting symptom of the disease, early diagnosis becomes essential. Genetic testing might be helpful in this regard, providing a definite diagnosis in some patients. Yet important limitations still exist, with a significant proportion of patients remaining with no causative mutation identifiable after genetic testing. This review aims to provide the latest knowledge on the genetic basis of cardiac channelopathies and discuss the role of the affected proteins in the pathophysiology of each one of these diseases.

Whole exome sequencing identifies a novel mutation (c.333 + 2T > C) of TNNI3K in a Chinese family with dilated cardiomyopathy and cardiac conduction disease

Dilated Cardiomyopathy (DCM) and cardiac conduction disease (CCD) are two kinds if diseases that can induce heart failure, syncope and even sudden cardiac death (SCD). DCM patients can experience CCD at the same time. In recent research, some disease-causing genes and variants have been identified in patients with DCM and CCD, such as Alpha-Actinin-2 and TNNI3 Interacting Kinase (TNNI3K). In this study, we employed whole-exome sequencing (WES) to explore the potential causative genes in a Chinese family with DCM and CCD. A novel splice site mutation (c.333 + 2 T > C) of TNNI3K was identified and co-segregated with the affected family members. This novel mutation was also absent in 200 healthy local controls and predicted to be disease-causing by Mutationtaster. The splice site mutation (c.333 + 2 T > C) may result in a premature stop codon in exon 4 of the TNNI3K gene and can induce nonsense-mediated mRNA decay. Real-time qPCR also confirmed that the level of TNNI3K mRNA expression was decreased significantly compared with the controls, which may lead to myocardial structural disorder and arrhythmia. In this study we reported the third novel mutation of TNNI3K in DCM and CCD patients which further supported the important role of TNNI3K in heart development and expanded the spectrum of TNNI3K mutations. The results may contribute to the genetic diagnosis and counseling of families with DCM and CCD.

Targeted next generation sequencing in a young population with suspected inherited malignant cardiac arrhythmias

Aborted sudden cardiac death in the young often is due to inherited heart disease. However, the clinical phenotype in these patients is not always evident. The aim of this study was to identify pathogenic molecular genetic variants in a population with suspected inherited cardiac arrhythmias. Eligible patients were admitted to Aarhus University Hospital, Denmark during the period 1999–2013 with arrhythmias assumed caused by a hereditary heart disease, and in whom no genotype had been established. We used the Danish national pacemaker and ICD registry to identify this cohort. One third (24/80) of the study population had first-line genetic testing with a targeted next-generation sequencing (NGS) panel, and two-third (56/80) of the study population had second-line genetic testing with NGS where prior Sanger sequencing did not reveal a causative variant. Variants were assessed according to the American College of Medical Genetics and Genomics (ACMG) guidelines. We included 80 patients. Median age (IQR) was 38 (28–43) years, 54 (68%) were males. First-line genetic testing identified a genetic variant in 33% (8/24) of the cases and second-line genetic testing revealed a variant in 20% (11/56) of the cases. Eleven variants were considered pathogenic, three likely pathogenic and 10 were variants of unknown significance (VUS). Seventeen variants were very rare with a minor allele frequency (MAF) ≤0.02% in all population databases used in the study. Molecular genetic testing of patients with suspected inherited cardiac arrhythmias with NGS identifies a molecular-genetic cause in a significant proportion of patients.

Gating Pore Currents in Sodium Channels

Voltage-gated sodium channels belong to the superfamily of voltage-gated cation channels. Their structure is based on domains comprising a voltage sensor domain (S1-S4 segments) and a pore domain (S5-S6 segments). Mutations in positively charged residues of the S4 segments may allow protons or cations to pass directly through the gating pore constriction of the voltage sensor domain; these anomalous currents are referred to as gating pore or omega (ω) currents. In the skeletal muscle disorder hypokalemic periodic paralysis, and in arrhythmic dilated cardiomyopathy, inherited mutations of S4 arginine residues promote omega currents that have been shown to be a contributing factor in the pathogenesis of these sodium channel disorders. Characterization of gating pore currents in these channelopathies and with artificial mutations has been possible by measuring the voltage-dependence and selectivity of these leak currents. The basis of gating pore currents and the structural basis of S4 movement through the gating pore has also been studied extensively with molecular dynamics. These simulations have provided valuable insight into the nature of S4 translocation and the physical basis for the effects of mutations that promote permeation of protons or cations through the gating pore.

Determinants of occurrence and survival after sudden cardiac arrest-A European perspective: The ESCAPE-NET project

AIMS

The ESCAPE-NET project ("European Sudden Cardiac Arrest network- towards Prevention, Education and New Effective Treatments") aims to study: (1) risk factors and mechanisms for the occurrence of sudden cardiac arrest (SCA) in the population, and (2) risk factors and treatment strategies for survival after SCA on a European scale.

METHODS

This is an Horizon2020 funded program of the European Union, performed by a European public-private consortium of 16 partners across 10 EU countries. There are 11 deep-phenotyped SCA cohorts for the study of risk factors and treatment strategies for survival after SCA, and 5 deep-phenotyped observational prospective population cohorts for the study of risk factors for occurrence of SCA. Personalized risk scores for predicting SCA onset and for predicting survival after SCA will be derived and validated.

RESULTS

The 11 clinical studies with SCA cases comprise 85,790 SCA cases; the 5 observational prospective population cohorts include 53,060 subjects. A total of 15,000 SCA samples will be genotyped for common and rare variants at the Helmholtz Zentrum München (Germany) using the Illumina Global Screening Array which contains > 770,000 SNPs, and after imputation, a database of an estimated > 9 million variants will be available for genome wide association studies. Standardization of risk factors definition and outcomes is ongoing. An Executive Committee has been created along with a Collaboration Policy document.

CONCLUSION

ESCAPE-NET will complement ongoing efforts on SCA outside Europe and within Europe including the EuReCa project.

Using the genome aggregation database, computational pathogenicity prediction tools, and patch clamp heterologous expression studies to demote previously published long QT syndrome type 1 mutations from pathogenic to benign

BACKGROUND

Mutations in the KCNQ1-encoded Kv7.1 potassium channel cause long QT syndrome (LQTS) type 1 (LQT1). It has been suggested that ∼10%-20% of rare LQTS case-derived variants in the literature may have been published erroneously as LQT1-causative mutations and may be "false positives."

OBJECTIVE

The purpose of this study was to determine which previously published KCNQ1 case variants are likely false positives.

METHODS

A list of all published, case-derived KCNQ1 missense variants (MVs) was compiled. The occurrence of each MV within the Genome Aggregation Database (gnomAD) was assessed. Eight in silico tools were used to predict each variant's pathogenicity. Case-derived variants that were either (1) too frequently found in gnomAD or (2) absent in gnomAD but predicted to be pathogenic by ≤2 tools were considered potential false positives. Three of these variants were characterized functionally using whole-cell patch clamp technique.

RESULTS

Overall, there were 244 KCNQ1 case-derived MVs. Of these, 29 (12%) were seen in ≥10 individuals in gnomAD and are demotable. However, 157 of 244 MVs (64%) were absent in gnomAD. Of these, 7 (4%) were predicted to be pathogenic by ≤2 tools, 3 of which we characterized functionally. There was no significant difference in current density between heterozygous KCNQ1-F127L, -P477L, or -L619M variant-containing channels compared to KCNQ1-WT.

CONCLUSION

This study offers preliminary evidence for the demotion of 32 (13%) previously published LQT1 MVs. Of these, 29 were demoted because of their frequent sighting in gnomAD. Additionally, in silico analysis and in vitro functional studies have facilitated the demotion of 3 ultra-rare MVs (F127L, P477L, L619M).

[Sudden cardiac death : Epidemiology, pathophysiology and risk stratification]

Sudden cardiac death (SCD) remains a major public health burden despite revolutionary progress in the last three decades in the treatment of ventricular tachyarrhythmia with the use of implantable cardioverter defibrillator (ICD) therapy. Survivors of sudden cardiac arrest are at high risk for recurrent tachyarrhythmia events. Early recognition of low left ventricular ejection fractions (≤35%) as a strong predictor of mortality and the causal association between ventricular tachyarrhythmia and SCD has led to a significant development of not only pharmacological antiarrhythmic therapy but also device-based prevention of SCD. The ICD therapy is nowadays routinely used for primary prevention of SCD in patients with significant structural cardiomyopathy and primary electrical arrhythmia syndromes, which are associated with high a risk and secondary prevention in survivors of sudden cardiac arrest. Additionally, effective approaches exist to significantly reduce the recurrence rate of ventricular tachyarrhythmia of various origins by complex electrophysiological endocardial and epicardial catheter ablation procedures.

When signalling goes wrong: pathogenic variants in structural and signalling proteins causing cardiomyopathies

Cardiomyopathies are a diverse group of cardiac disorders with distinct phenotypes, depending on the proteins and pathways affected. A substantial proportion of cardiomyopathies are inherited and those will be the focus of this review article. With the wide application of high-throughput sequencing in the practice of clinical genetics, the roles of novel genes in cardiomyopathies are recognised. Here, we focus on a subgroup of cardiomyopathy genes [TTN, FHL1, CSRP3, FLNC and PLN, coding for Titin, Four and a Half LIM domain 1, Muscle LIM Protein, Filamin C and Phospholamban, respectively], which, despite their diverse biological functions, all have important signalling functions in the heart, suggesting that disturbances in signalling networks can contribute to cardiomyopathies.

Whole-exome sequencing identifies a novel mutation of GPD1L (R189X) associated with familial conduction disease and sudden death

Cardiac conduction disease (CCD) is a serious disorder and the leading cause of mortality worldwide. It is characterized by arrhythmia, syncope or even sudden cardiac death caused by the dysfunction of cardiac voltage‐gated channel. Previous study has demonstrated that mutations in genes encoding voltage‐gated channel and related proteins were the crucial genetic lesion of CCD. In this study, we employed whole‐exome sequencing to explore the potential causative genes in a Chinese family with ventricular tachycardia and syncope. A novel nonsense mutation (c.565C>T/p.R189X) of glycerol‐3‐phosphate dehydrogenase‐like (GPD1L) was identified and co‐segregated with the affected family members. GPD1L is a crucial interacting protein of SCN5A, a gene encoded sodium channel α‐subunit Na_v1.5 and mainly associated with Brugada syndrome (BrS). The novel mutation (c.565C>T/p.R189X) may result in a premature stop codon at position 189 in exon 4 of the GPD1L gene and lead to functional haploinsufficiency of GPD1L due to mRNA carrying this mutation will be degraded by nonsense‐mediated mRNA decay, which has been confirmed by Western blot in HEK293 cells transfected HIS‐GPD1L plasmid. The levels of GPD1L decreasing may disturb the function of Na_v1.5 and induce arrhythmia and syncope in the end. In conclusion, our study not only further supported the important role of GPD1L in CCD, but also expanded the spectrum of GPD1L mutations and will contribute to the genetic diagnosis and counselling of families with CCD.

Long-term intra-individual reproducibility of heart rate dynamics during exercise and recovery in the UK Biobank cohort

Background

The heart rate (HR) response to exercise provides useful information about the autonomic function and has prognostic value, but its reproducibility over a long period of time, a critical requirement for using it as a clinical biomarker, is undetermined.

Aim

To determine the intra-individual reproducibility of HR dynamics during sub-maximum exercise and one minute recovery.

Methods

1187 individuals from the Cardio physical fitness assessment test of the UK Biobank repeated a standard exercise stress test twice (recall time 34.2 ± 2.8 months) and were prospectively studied.

Results

821 individuals complied with inclusion criteria for reproducibility analysis, including peak workload differences between assessments ≤10 W. Intra-individual correlation between HR profile during the first and the second assessment was very high and higher than inter-individual correlation (0.92±0.08 vs 0.87±0.11, p<0.01). Intra-individual correlation of indices describing HR dynamics was: ρ = 0.81 for maximum HR during exercise; ρ = 0.71 for minimum HR during recovery; ρ = 0.70 for HR changes during both exercise and recovery; Intra-individual correlation was higher for these indices of HR dynamics than for resting HR (ρ = 0.64). Bland-Altman plots demonstrated good agreement between HR indices estimated during the first and second assessment. A small but consistent bias was registered for all repeated measurements. The intra-individual consistency of abnormal values was about 60–70%.

Conclusions

The HR dynamics during exercise and recovery are reproducible over a period of 3 years, with moderate to strong intra-individual reproducibility of abnormal values.

Recent advances in understanding and prevention of sudden cardiac death

There have been tremendous advances in the diagnosis and treatment of heart disease over the last 50 years. Nevertheless, it remains the number one cause of death. About half of heart-related deaths occur suddenly, and in about half of these cases the person was unaware that they had underlying heart disease. Genetic heart disease accounts for only approximately 2% of sudden cardiac deaths, but as it typically occurs in younger people it has been a particular focus of activity in our quest to not only understand the underlying mechanisms of cardiac arrhythmogenesis but also develop better strategies for earlier detection and prevention. In this brief review, we will highlight trends in the recent literature focused on sudden cardiac death in genetic heart diseases and how these studies are contributing to a broader understanding of sudden death in the community.