Abstract Background/Introduction Brugada syndrome (BrS) is an inherited arrhythmia condition that can cause sudden cardiac death. Rare coding and common non-coding genetic variation in the Nav1.5 cardiac sodium channel-encoding SCN5A gene is robustly associated with BrS, but the role of rare and low frequency non-coding variants remains unexplored. BrS is several times more prevalent in Southeast Asia compared to other populations, indicating ancestry-specific genetic risk factors remain to be discovered. Purpose To identify and characterise novel genetic risk factors in BrS patients from Southeast Asia. Methods We performed genome sequencing in 231 BrS probands from Thailand and 500 population-matched controls to identify novel disease associated variants across the entire SCN5A locus. The candidate variant was engineered into human induced pluripotent stem cells (hiPSCs) by CRISPR-Cas9 and its effect was evaluated by single cell electrophysiology analysis on hiPSC-derived cardiomyocytes. Results We identified a rare (absent in gnomAD), non-coding variant in a regulatory element of the SCN5A gene (GRCh38:3-38580380-A-C) that was significantly enriched in cases (3.9%) vs controls (0.2%) (OR=20.2[2.5-160.6], p=2e-04). Transcription factor motif scanning analysis suggested the variant is likely to disrupt a Mef2 site that is conserved across species (Figure 1) – the MEF2 family of transcription factors play a critical role in cardiac transcriptional regulation. In hiPSC-derived cardiomyocytes, a significant reduction of peak Nav1.5-mediated sodium-current (INa) density (30% decrease at -20mV, p=8e-03), without changes in gating properties, was observed in cardiomyocytes carrying the variant in heterozygosity compared to isogenic controls (Figure 2). The variant also significantly reduced luciferase activity of the candidate regulatory element in HEK cells in the presence of cardiac transcription factors (Tbx5, Gata4, Mef2A, Mef2D). Conclusion A novel, non-coding variant in an SCN5A enhancer region is associated with BrS and was functionally validated using single cell electrophysiology in hiPSC-derived cardiomyocytes. This variant is found in ∼1 in every 25 BrS patients from Thailand and therefore may at least partially explain the increased prevalence of BrS in this region. Our study highlights the importance of research in understudied populations to understand the genetic aetiology of disease in diverse ancestries and to identify novel disease risk factors.

Abstract The Brugada Syndrome (BrS) is characterized by ST-segment elevation in the right precordial leads and is associated with an increased risk of sudden cardiac death. The disorder was initially described as a monogenic primary cardiac electrical disease. However, mutations in SCN5A, encoding the cardiac sodium channel (NaV1.5), which is the major gene associated with the disorder are found in only around 20% of cases and are associated with low penetrance. Furthermore many cases did not display familial aggregation. Based on a previous GWAS conducted on 312 BrS patients and the discovery of the unexpected strong effect of 3 common variants, we proposed that the BrS may comprise a more complex inheritance model. We conducted a genome-wide association study on 2820 individuals with BrS and 10001 ancestry-matched controls to uncover additional genetic loci that modulate susceptibility to BrS, to characterize further the BrS genetic architecture and to uncover new molecular mechanisms. We identified 21 susceptibility variants that passed the genome-wide statistical significance threshold (P<5.10–8), of which 18 were novel. Eight were located at the SCN5A-SCN10A locus, illustrating the central role of NaV1.5 in the disease. Interestingly, 9 occur in the vicinity of genes known to play a crucial role in cardiac development (HEY2, TBX20, GATA4, ZFPM2, WT1, TBX5, IRX3, IRX5) and / or control cardiac ion channel expression. Of note, 2 others signals occurred in the vicinity of microtubule / cytoskeleton associated proteins (MAPRE2 and MYO18B). Through studies in zebrafish and in human iPSC-derived cardiomyocytes, we demonstrate a role of MAPRE2 on NaV1.5 function. We identified 18 new susceptibility variants associated with BrS and uncovered a new pathophysiological molecular mechanism underlying BrS susceptibility. We provided further support for a complex genetic architecture underlying susceptibility for the disorder. Funding Acknowledgement Type of funding source: Public Institution(s). Main funding source(s): H2020 - Marie Sklodowska Curie IF grant, Rising star grant from the Pays de la Loire regional council

Symptomatic fetal long QT syndrome (fLQTS) is often misdiagnosed as knowledge of cardiac phenotypes is scarce. Inappropriate management with QT prolonging medication can be fatal. We performed a systematic review (SR) to describe the clinical presentation and potential genotype-phenotype correlations in fLQTS. This SR was performed in in MEDLINE and EMBASE up till December 2018. Two reviewers independently screened all studies, assessed eligibility and extracted data. Cohort studies, case series or case reports describing the fLQTS phenotype were included. Information regarding the heart rate, arrhythmias, age of first arrhythmias, QTc times, genotype, and outcome was collected. A total of 161 full-text articles describing 432 fLQTS cases were included. Sinus bradycardia was seen in 148 (44,6%) cases. Prenatally, the mean atrial rate was 126±69 and the ventricular rate 108±45/min. Ventricular tachycardia (VT) or atrio-ventricular block (AVB), (predominantly 2:1), was seen in 97 fetuses, of whom 33 (33%) died. The median age of first VT/AVB (n = 76) was 27 weeks of gestation. The highest risk for arrhythmias was in compound or homozygous variant carriers and probands. T613M, T613K (LQTS2) and R1623Q (LQTS3) were malignant heterozygous genotypes. The longest QTc times were recorded in fetuses with only 2:1AVB (m 639±110 msec). In LQTS1 sinus bradycardia was the signature rhythm (n = 43) and 2:1AVB was only seen in Jervell Lange Nielsen Syndrome. In LQTS2, 2:1AVB was the most common arrhythmia and occurred with VT or Torsade de pointes (TdP) in 73%. 2:1AVB and/or VT were observed in 12 (23%) of LQTS3 cases. LQTS3 was most likely if VT/TdP was isolated or if AVB was variable. Sinus bradycardia is a feature of fLQTS. When VT/TdP and/or 2:1AVB is/are present, the mortality is high. Arrhythmias usually present around 28 weeks gestation. Genotype-phenotype correlations have been identified and can aid in the choice of anti-arrhythmic therapy.

We set out to identify the genetic defect underlying multiple cardiac manifestations in a Dutch family. Multiple family members presented with bradycardia in combination with hypertrabeculation of the myocardium. Atrial fibrillation, mitral valve complications and sudden cardiac death also occurred in the pedigree. We undertook a strategy consisting of first reducing the genome space by identifying chromosomal regions shared among affected individuals, followed by exome sequencing for identification of sequence variants within these regions. In our gene discovery effort we focused on the bradycardia phenotype as this could be assessed in most pedigree members and multiple affected individuals were available. Genome-wide SNP genotyping was carried out using the Illumina HumanOmni2.5 array. This genotypic data was used for identification of chromosomal regions shared identical-by-descent (IBD) among individuals affected with bradycardia, uncovering a total of 21 loci shared IBD. Exome sequencing was carried out on the 2 most distantly related individuals with bradycardia. The coding region of the genome was captured using the Agilent SureSelect Target enrichment system followed by sequencing on the Illumina Hiseq2000 platform. The SOAPsnp (for single nucleotide variants, SNVs) and the GATK (for copy number variants, CNVs) genome analysis algorithms were used for genotype calling. Variants were filtered against multiple exome and genome sequencing databases (e.g. dbSNP132, Exome Variant Server, 1000Genomes, Genome of the Netherlands). Seven novel and potentially malignant variants located within the 21 IBD regions were identified. Of these only one variant, p.G482R in HCN4, segregated with the combined bradycardia and hypertrabeculation phenotype in the family. HCN4 encodes the potassium/sodium hyperpolarization-activated cyclic nucleotide-gated channel 4, underlying the cardiac pacemaker funny current (If). In line with the role of If in pacemaker activity of the sinus node, mutations in HCN4 are an established cause of bradycardia and it is therefore highly likely that the identified variant underlies the bradycardia in the family. However, the association of an HCN4 variant with hypertrabeculation of the myocardium is novel. Investigation of HCN4 in additional families with this combined phenotype is currently ongoing in order to explore further the possible link between mutation in HCN4 and myocardial hypertrabeculation

Background— A rapidly growing number of long-QT syndrome (LQTS) patients are being treated with an implantable cardioverter-defibrillator (ICD). ICDs may pose problems, especially in the young. We sought to determine the characteristics of the LQTS patients receiving an ICD, the indications, and the aftermath. Methods and Results— The study population included 233 patients. Beginning in 2002, data were collected prospectively. Female patients (77%) and LQT3 patients (22% of genotype positive) were overrepresented; mean QTc was 516±65 milliseconds; mean age at implantation was 30±17 years; and genotype was known in 59% of patients. Unexpectedly, 9% of patients were asymptomatic before implantation. Asymptomatic patients, almost absent among LQT1 and LQT2 patients, represented 45% of LQT3 patients. Patients with cardiac symptoms made up 91% of all study participants, but only 44% had cardiac arrest before ICD implantation. In addition, 41% of patients received an ICD without having first been on LQTS therapy. During follow-up, 4.6±3.2 years, at least 1 appropriate shock was received by 28% of patients, and adverse events occurred in 25%. Appropriate ICD therapies were predicted by age <20 years at implantation, a QTc >500 milliseconds, prior cardiac arrest, and cardiac events despite therapy; within 7 years, appropriate shocks occurred in no patients with none of these factors and in 70% of those with all factors. Conclusions— Reflecting previous concepts, ICDs were implanted in some LQTS patients whose high risk now appears questionable. Refined criteria for implantation, reassessment of pros and cons, ICD reprogramming, and consideration for other existing therapeutic options are necessary.

Background— Brugada syndrome is characterized by ST-segment elevation in the right precordial leads and an increased risk of sudden cardiac death (SCD). Fundamental questions remain on the best strategy for assessing the real disease-associated arrhythmic risk, especially in asymptomatic patients. The aim of the present study was to evaluate the prognosis and risk factors of SCD in Brugada syndrome patients in the FINGER (France, Italy, Netherlands, Germany) Brugada syndrome registry. Methods and Results— Patients were recruited in 11 tertiary centers in 4 European countries. Inclusion criteria consisted of a type 1 ECG present either at baseline or after drug challenge, after exclusion of diseases that mimic Brugada syndrome. The registry included 1029 consecutive individuals (745 men; 72%) with a median age of 45 (35 to 55) years. Diagnosis was based on (1) aborted SCD (6%); (2) syncope, otherwise unexplained (30%); and (3) asymptomatic patients (64%). During a median follow-up of 31.9 (14 to 54.4) months, 51 cardiac events (5%) occurred (44 patients experienced appropriate implantable cardioverter-defibrillator shocks, and 7 died suddenly). The cardiac event rate per year was 7.7% in patients with aborted SCD, 1.9% in patients with syncope, and 0.5% in asymptomatic patients. Symptoms and spontaneous type 1 ECG were predictors of arrhythmic events, whereas gender, familial history of SCD, inducibility of ventricular tachyarrhythmias during electrophysiological study, and the presence of an SCN5A mutation were not predictive of arrhythmic events. Conclusions— In the largest series of Brugada syndrome patients thus far, event rates in asymptomatic patients were low. Inducibility of ventricular tachyarrhythmia and family history of SCD were not predictors of cardiac events.

La repolarisation précoce est une caractéristique électro cardiographique commune (1-5 % de la population générale). Une étude récente a montré que l'incidence de la repolarisation précoce (RP) est plus élevée chez les sujets ayant présenté une fibrillation ventriculaire (31 % des patients vs 5 % des contrôles). A ce jour, il est encore impossible de différencier les patients présentant un aspect de RP à risque parmi la population générale. L'existence de forme familiale de RP associée à des morts subites suggère un caractère héréditaire à cette pathologie. Une étude génétique a été réalisée sur une cohorte de 96 patients. Les gènes majeurs des troubles du rythme cardiaque et les genes codant les canaux ioniques impliqués dans la phase de repolarisation du potentiel d'action ventriculaire ont été exclus par séquençage chez ces patients. Les canaux potassiques ATP dépendant (KATP) sont fortement exprimés dans les cardiomyocytes. L'une des hypothèses émises est qu'une augmentation de 1-2 % de l'ouverture de ces canaux générerait un courant suffisant qui pourrait affecter la phase de repolarisation ventriculaire. Les canaux KATP sont composés de sous-unités canalaires Kir6.0 (KCNJ8 codant Kir6.1 ou KCNJ11 codant Kir6.2) et de récepteurs aux sulphonylurées SUR (ABCC8 codant SUR1 ou ABCC9 codant SUR2). L'approche gène-candidat a permis de mettre en évidence le variant rare p.S422L dans le gène KCNJ8 chez une jeune patiente présentant de nombreux épisodes de fibrillation ventriculaire (plus de 100) et une RP dans les dérivations inféro-latérales. Suite à ces premiers résultats, nous avons séquencés les autres sous-unités des canaux KATP. Ainsi, 5 variants ont été identifiés dans le gène ABCC9 : 4 variants faux-sens et une substitution d'un nucléotide dans un site d'epissage. L'enquête familiale et l'analyse fonctionnelle sont en cours pour ces patients. Plusieurs hypothèses physiopathologiques (augmentation du trafic membranaire, diminution de la sensibilité à l'ATP…) vont être testées afin de comprendre l'implication de ces variants sur le potentiel d'action ventriculaire. L'identification de 6 patients sur 96 (6.25 %) porteurs de variant dans les gènes codant les canaux KATP conforte l'hypothèse du rôle de ce courant dans le syndrome de repolarisation précoce.

BACKGROUND:Although it is known that cardiac resynchronization therapy (CRT) in heart failure (HF) patients improves systemic circulation, its acute effects on microcirculation are as yet unknown. Therefore we investigated the sublingual microcirculatory changes in HF patients from CRT and right ventricular (RV) pacing by use of orthogonal polarization spectral (OPS) imaging. METHODS AND RESULTS:Twelve consecutive HF patients with a CRT device and 20 healthy individuals (HI) were included. Acute microcirculatory changes were assessed by functional capillary density (FCD) and capillary velocity (CV) measurement 6 months after CRT. FCD and CV were measured in HF patients sublingually after 15 minutes of programming 1 of 3 pacing modalities in random order (no pacing, RV pacing, and CRT). FCD was significantly higher in HI (11.2 +/- 2.1 cm/cm(2)) compared with HF patients with RV pacing (8.9 +/- 1.9 cm/cm(2); P = .03) and no pacing (8.3 +/- 2.4 cm/cm(2); P = .02). CRT (12.1 +/- 2.2 cm/cm(2)) significantly increased FCD in HF patients compared with RV pacing (8.9 +/- 1.9 cm/cm(2); P = .006) and no pacing (8.3 +/- 2.4 cm/cm(2); P = .008). CV was normal in all patients with or without pacing. CONCLUSIONS:CRT improves microcirculatory function as assessed by OPS imaging.

Aims Hypertrophic cardiomyopathy (HCM) is caused by mutations in genes that encode sarcomeric proteins. In this study we investigated the involvement of the sarcomeric myosin binding protein C in the Dutch HCM population.Methods and results We initially. screened 22 Dutch index patients for mutations in the MYBPC3 gene, which revealed four different mutations in 14 patients. The 2373insG mutation was identified in 10 apparently unrelated patients. A subsequent screening for the 2373insG mutation in a group of another 237 unrelated HCM patients revealed 50 additional carriers of the same genetic defect. Genotyping with polymorphic repeat markers and intragenic SNPs of the 60 Dutch as well as two German and five North American 2373insG carriers indicated they all share the same haplotype.Conclusion The 2373insG mutation accounts for almost one-fourth of all HCM cases in the Netherlands (60/259), which is predominantly present in the northwestern part of the country (22/66) and is a founder mutation probably originating from the Netherlands. (C) 2003 Published by Elsevier Ltd on behalf of The European Society of Cardiology.

Objectives: The KCNQ1 gene encodes the KvLQT1 potassium channel, which generates in the human heart the slow component of the cardiac delayed rectifier current, I-Kc. Mutations in KCNQ1 are the most frequent cause of the congenital long QT syndrome. We have previously cloned a cardiac KCNQ1 human isoform, which exerts a strong dominant-negative effect on KvLQT1 channels. We took advantage of this dominant-negative isoform to engineer an in vivo model of KvLQT1 disruption, obtained by overexpressing the dominant-negative subunit under the control of the a-myosin heavy chain promoter. Results: Three different transgenic lines demonstrated a phenotype with increasing severity. Functional suppression of KvLQT1 in transgenic mice led to a markedly prolonged QT interval associated with sinus node dysfunction. Transgenic mice also demonstrated atrio-ventricular block leading to occasional Wenckebach phenomenon. The atrio-ventricular block was associated with prolonged AH but normal HV interval in His recordings. Prolonged QT interval correlated with prolonged action potential duration and with reduced K+ current density in patch-clamp experiments. RNase protection assay revealed remodeling of K+ channel expression in transgenic mice. Conclusions: Our transgenic mouse model suggests a role for KvLQT1 channels not only in the mouse cardiac repolarisation but also in the sinus node automaticity and in the propagation of the impulse through the AV node. (C) 2001 Elsevier Science B.V. All rights reserved.

Mutations in the KvLQT1 gene are the cause of the long QT syndrome I, KvLQT1 gene product is associated with the regulator protein IsK to produce a component of the delayed rectifier K+ current in cardiac myocytes, We identified an N-terminal truncated isoform of the KvLQT1 gene product, referred to as isoform 2, In RNase protection assays, isoform 2 represented 28.1 +/- 0.6% of the total KvLQT1 expression in the human adult ventricle, COS-7 cells injected intranuclearly with KvLQT1 isoform 1 cDNA exhibited a fast-activating K+ current, whereas those injected with a KvLQT1 isoform 1 plus IsK cDNA showed a slow-activating K+ current, Cells injected with KvLQT1 isoform 2 plasmid showed no detectable K+ current, Those injected with a 1/1 isoform 2/isoform 1 ratio showed no detectable H+ current, Those injected with 1/5 and 2/5 ratios showed a K+ current with markedly reduced amplitude, Coexpression of the IsK regulator consistently reduced the dominant negative effects of isoform 2, Our results indicate that KvLQT1 isoform 2 exerts a pronounced negative dominance on isoform 1 channels and that the cardiac KvLQT1 K+ channel complex is composed of at least three different proteins as follows: isoform 1, isoform 2, and IsK.