Publications by authors named "Leander Beekman"

27 Publications

  • Page 1 of 1

Biallelic loss-of-function variants in PLD1 cause congenital right-sided cardiac valve defects and neonatal cardiomyopathy.

J Clin Invest 2021 03;131(5)

Amsterdam UMC, University of Amsterdam, Heart Center, Department of Clinical and Experimental Cardiology, Amsterdam Cardiovascular Sciences.

Congenital heart disease is the most common type of birth defect, accounting for one-third of all congenital anomalies. Using whole-exome sequencing of 2718 patients with congenital heart disease and a search in GeneMatcher, we identified 30 patients from 21 unrelated families of different ancestries with biallelic phospholipase D1 (PLD1) variants who presented predominantly with congenital cardiac valve defects. We also associated recessive PLD1 variants with isolated neonatal cardiomyopathy. Furthermore, we established that p.I668F is a founder variant among Ashkenazi Jews (allele frequency of ~2%) and describe the phenotypic spectrum of PLD1-associated congenital heart defects. PLD1 missense variants were overrepresented in regions of the protein critical for catalytic activity, and, correspondingly, we observed a strong reduction in enzymatic activity for most of the mutant proteins in an enzymatic assay. Finally, we demonstrate that PLD1 inhibition decreased endothelial-mesenchymal transition, an established pivotal early step in valvulogenesis. In conclusion, our study provides a more detailed understanding of disease mechanisms and phenotypic expression associated with PLD1 loss of function.
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March 2021

Systematic large-scale assessment of the genetic architecture of left ventricular noncompaction reveals diverse etiologies.

Genet Med 2021 Jan 26. Epub 2021 Jan 26.

Amsterdam UMC, University of Amsterdam, Department of Clinical and Experimental Cardiology, Heart Centre, Amsterdam, Netherlands.

Purpose: To characterize the genetic architecture of left ventricular noncompaction (LVNC) and investigate the extent to which it may represent a distinct pathology or a secondary phenotype associated with other cardiac diseases.

Methods: We performed rare variant association analysis with 840 LVNC cases and 125,748 gnomAD population controls, and compared results to similar analyses on dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM).

Results: We observed substantial genetic overlap indicating that LVNC often represents a phenotypic variation of DCM or HCM. In contrast, truncating variants in MYH7, ACTN2, and PRDM16 were uniquely associated with LVNC and may reflect a distinct LVNC etiology. In particular, MYH7 truncating variants (MYH7tv), generally considered nonpathogenic for cardiomyopathies, were 20-fold enriched in LVNC cases over controls. MYH7tv heterozygotes identified in the UK Biobank and healthy volunteer cohorts also displayed significantly greater noncompaction compared with matched controls. RYR2 exon deletions and HCN4 transmembrane variants were also enriched in LVNC, supporting prior reports of association with arrhythmogenic LVNC phenotypes.

Conclusion: LVNC is characterized by substantial genetic overlap with DCM/HCM but is also associated with distinct noncompaction and arrhythmia etiologies. These results will enable enhanced application of LVNC genetic testing and help to distinguish pathological from physiological noncompaction.
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January 2021

Shared genetic pathways contribute to risk of hypertrophic and dilated cardiomyopathies with opposite directions of effect.

Nat Genet 2021 02 25;53(2):128-134. Epub 2021 Jan 25.

Department of Clinical and Experimental Cardiology, Heart Center, Amsterdam Cardiovascular Sciences, University of Amsterdam, Amsterdam UMC, Amsterdam, the Netherlands.

The heart muscle diseases hypertrophic (HCM) and dilated (DCM) cardiomyopathies are leading causes of sudden death and heart failure in young, otherwise healthy, individuals. We conducted genome-wide association studies and multi-trait analyses in HCM (1,733 cases), DCM (5,521 cases) and nine left ventricular (LV) traits (19,260 UK Biobank participants with structurally normal hearts). We identified 16 loci associated with HCM, 13 with DCM and 23 with LV traits. We show strong genetic correlations between LV traits and cardiomyopathies, with opposing effects in HCM and DCM. Two-sample Mendelian randomization supports a causal association linking increased LV contractility with HCM risk. A polygenic risk score explains a significant portion of phenotypic variability in carriers of HCM-causing rare variants. Our findings thus provide evidence that polygenic risk score may account for variability in Mendelian diseases. More broadly, we provide insights into how genetic pathways may lead to distinct disorders through opposing genetic effects.
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February 2021

Functional modulation of atrio-ventricular conduction by enhanced late sodium current and calcium-dependent mechanisms in Scn5a1798insD/+ mice.

Europace 2020 10;22(10):1579-1589

Department of Clinical and Experimental Cardiology, Amsterdam UMC, Heart Center, Academic Medical Center, Room K2-104.2, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.

Aims: SCN5A mutations are associated with arrhythmia syndromes, including Brugada syndrome, long QT syndrome type 3 (LQT3), and cardiac conduction disease. Long QT syndrome type 3 patients display atrio-ventricular (AV) conduction slowing which may contribute to arrhythmogenesis. We here investigated the as yet unknown underlying mechanisms.

Methods And Results: We assessed electrophysiological and molecular alterations underlying AV-conduction abnormalities in mice carrying the Scn5a1798insD/+ mutation. Langendorff-perfused Scn5a1798insD/+ hearts showed prolonged AV-conduction compared to wild type (WT) without changes in atrial and His-ventricular (HV) conduction. The late sodium current (INa,L) inhibitor ranolazine (RAN) normalized AV-conduction in Scn5a1798insD/+ mice, likely by preventing the mutation-induced increase in intracellular sodium ([Na+]i) and calcium ([Ca2+]i) concentrations. Indeed, further enhancement of [Na+]i and [Ca2+]i by the Na+/K+-ATPase inhibitor ouabain caused excessive increase in AV-conduction time in Scn5a1798insD/+ hearts. Scn5a1798insD/+ mice from the 129P2 strain displayed more severe AV-conduction abnormalities than FVB/N-Scn5a1798insD/+ mice, in line with their larger mutation-induced INa,L. Transverse aortic constriction (TAC) caused excessive prolongation of AV-conduction in FVB/N-Scn5a1798insD/+ mice (while HV-intervals remained unchanged), which was prevented by chronic RAN treatment. Scn5a1798insD/+-TAC hearts showed decreased mRNA levels of conduction genes in the AV-nodal region, but no structural changes in the AV-node or His bundle. In Scn5a1798insD/+-TAC mice deficient for the transcription factor Nfatc2 (effector of the calcium-calcineurin pathway), AV-conduction and conduction gene expression were restored to WT levels.

Conclusions: Our findings indicate a detrimental role for enhanced INa,L and consequent calcium dysregulation on AV-conduction in Scn5a1798insD/+ mice, providing evidence for a functional mechanism underlying AV-conduction disturbances secondary to gain-of-function SCN5A mutations.
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October 2020

Transethnic Genome-Wide Association Study Provides Insights in the Genetic Architecture and Heritability of Long QT Syndrome.

Najim Lahrouchi Rafik Tadros Lia Crotti Yuka Mizusawa Pieter G Postema Leander Beekman Roddy Walsh Kanae Hasegawa Julien Barc Marko Ernsting Kari L Turkowski Andrea Mazzanti Britt M Beckmann Keiko Shimamoto Ulla-Britt Diamant Yanushi D Wijeyeratne Yu Kucho Tomas Robyns Taisuke Ishikawa Elena Arbelo Michael Christiansen Annika Winbo Reza Jabbari Steven A Lubitz Johannes Steinfurt Boris Rudic Bart Loeys M Ben Shoemaker Peter E Weeke Ryan Pfeiffer Brianna Davies Antoine Andorin Nynke Hofman Federica Dagradi Matteo Pedrazzini David J Tester J Martijn Bos Georgia Sarquella-Brugada Óscar Campuzano Pyotr G Platonov Birgit Stallmeyer Sven Zumhagen Eline A Nannenberg Jan H Veldink Leonard H van den Berg Ammar Al-Chalabi Christopher E Shaw Pamela J Shaw Karen E Morrison Peter M Andersen Martina Müller-Nurasyid Daniele Cusi Cristina Barlassina Pilar Galan Mark Lathrop Markus Munter Thomas Werge Marta Ribasés Tin Aung Chiea C Khor Mineo Ozaki Peter Lichtner Thomas Meitinger J Peter van Tintelen Yvonne Hoedemaekers Isabelle Denjoy Antoine Leenhardt Carlo Napolitano Wataru Shimizu Jean-Jacques Schott Jean-Baptiste Gourraud Takeru Makiyama Seiko Ohno Hideki Itoh Andrew D Krahn Charles Antzelevitch Dan M Roden Johan Saenen Martin Borggrefe Katja E Odening Patrick T Ellinor Jacob Tfelt-Hansen Jonathan R Skinner Maarten P van den Berg Morten Salling Olesen Josep Brugada Ramón Brugada Naomasa Makita Jeroen Breckpot Masao Yoshinaga Elijah R Behr Annika Rydberg Takeshi Aiba Stefan Kääb Silvia G Priori Pascale Guicheney Hanno L Tan Christopher Newton-Cheh Michael J Ackerman Peter J Schwartz Eric Schulze-Bahr Vincent Probst Minoru Horie Arthur A Wilde Michael W T Tanck Connie R Bezzina

Circulation 2020 Jul 20;142(4):324-338. Epub 2020 May 20.

Amsterdam UMC, University of Amsterdam, Heart Center; Department of Clinical and Experimental Cardiology, Amsterdam Cardiovascular Sciences, The Netherlands (N.L., R.T., Y.M., P.G.P., L.B., R.W., N.H., H.L.T., A.A.W., C.R.B.).

Background: Long QT syndrome (LQTS) is a rare genetic disorder and a major preventable cause of sudden cardiac death in the young. A causal rare genetic variant with large effect size is identified in up to 80% of probands (genotype positive) and cascade family screening shows incomplete penetrance of genetic variants. Furthermore, a proportion of cases meeting diagnostic criteria for LQTS remain genetically elusive despite genetic testing of established genes (genotype negative). These observations raise the possibility that common genetic variants with small effect size contribute to the clinical picture of LQTS. This study aimed to characterize and quantify the contribution of common genetic variation to LQTS disease susceptibility.

Methods: We conducted genome-wide association studies followed by transethnic meta-analysis in 1656 unrelated patients with LQTS of European or Japanese ancestry and 9890 controls to identify susceptibility single nucleotide polymorphisms. We estimated the common variant heritability of LQTS and tested the genetic correlation between LQTS susceptibility and other cardiac traits. Furthermore, we tested the aggregate effect of the 68 single nucleotide polymorphisms previously associated with the QT-interval in the general population using a polygenic risk score.

Results: Genome-wide association analysis identified 3 loci associated with LQTS at genome-wide statistical significance (<5×10) near , , and , and 1 missense variant in (p.Asp85Asn) at the suggestive threshold (<10). Heritability analyses showed that ≈15% of variance in overall LQTS susceptibility was attributable to common genetic variation ( 0.148; standard error 0.019). LQTS susceptibility showed a strong genome-wide genetic correlation with the QT-interval in the general population (r=0.40; =3.2×10). The polygenic risk score comprising common variants previously associated with the QT-interval in the general population was greater in LQTS cases compared with controls (<10-13), and it is notable that, among patients with LQTS, this polygenic risk score was greater in patients who were genotype negative compared with those who were genotype positive (<0.005).

Conclusions: This work establishes an important role for common genetic variation in susceptibility to LQTS. We demonstrate overlap between genetic control of the QT-interval in the general population and genetic factors contributing to LQTS susceptibility. Using polygenic risk score analyses aggregating common genetic variants that modulate the QT-interval in the general population, we provide evidence for a polygenic architecture in genotype negative LQTS.
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July 2020

Predicting cardiac electrical response to sodium-channel blockade and Brugada syndrome using polygenic risk scores.

Eur Heart J 2019 10;40(37):3097-3107

Department of Clinical and Experimental Cardiology, Amsterdam UMC, University of Amsterdam, Heart Center, Amsterdam Cardiovascular Sciences, Meibergdreef 9, AZ Amsterdam, The Netherlands.

Aims: Sodium-channel blockers (SCBs) are associated with arrhythmia, but variability of cardiac electrical response remains unexplained. We sought to identify predictors of ajmaline-induced PR and QRS changes and Type I Brugada syndrome (BrS) electrocardiogram (ECG).

Methods And Results: In 1368 patients that underwent ajmaline infusion for suspected BrS, we performed measurements of 26 721 ECGs, dose-response mixed modelling and genotyping. We calculated polygenic risk scores (PRS) for PR interval (PRSPR), QRS duration (PRSQRS), and Brugada syndrome (PRSBrS) derived from published genome-wide association studies and used regression analysis to identify predictors of ajmaline dose related PR change (slope) and QRS slope. We derived and validated using bootstrapping a predictive model for ajmaline-induced Type I BrS ECG. Higher PRSPR, baseline PR, and female sex are associated with more pronounced PR slope, while PRSQRS and age are positively associated with QRS slope (P < 0.01 for all). PRSBrS, baseline QRS duration, presence of Type II or III BrS ECG at baseline, and family history of BrS are independently associated with the occurrence of a Type I BrS ECG, with good predictive accuracy (optimism-corrected C-statistic 0.74).

Conclusion: We show for the first time that genetic factors underlie the variability of cardiac electrical response to SCB. PRSBrS, family history, and a baseline ECG can predict the development of a diagnostic drug-induced Type I BrS ECG with clinically relevant accuracy. These findings could lead to the use of PRS in the diagnosis of BrS and, if confirmed in population studies, to identify patients at risk for toxicity when given SCB.
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October 2019

GATA6 mutations: Characterization of two novel patients and a comprehensive overview of the GATA6 genotypic and phenotypic spectrum.

Am J Med Genet A 2019 09 12;179(9):1836-1845. Epub 2019 Jul 12.

Department of Clinical Genetics, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands.

The first human mutations in GATA6 were described in a cohort of patients with persistent truncus arteriosus, and the phenotypic spectrum has expanded since then. This study underscores the broad phenotypic spectrum by presenting two patients with de novo GATA6 mutations, both exhibiting complex cardiac defects, pancreatic, and other abnormalities. Furthermore, we provided a detailed overview of all published human genetic variation in/near GATA6 published to date and the associated phenotypes (n = 78). We conclude that the most common phenotypes associated with a mutation in GATA6 were structural cardiac and pancreatic abnormalities, with a penetrance of 87 and 60%, respectively. Other common malformations were gallbladder agenesis, congenital diaphragmatic hernia, and neurocognitive abnormalities, mostly developmental delay. Fifty-eight percent of the mutations were de novo, and these patients more often had an anomaly of intracardiac connections, an anomaly of the great arteries, and hypothyroidism, compared with those with inherited mutations. Functional studies mostly support loss-of-function as the pathophysiological mechanism. In conclusion, GATA6 mutations give a wide range of phenotypic defects, most frequently malformations of the heart and pancreas. This highlights the importance of detailed clinical evaluation of identified carriers to evaluate their full phenotypic spectrum.
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September 2019

Enhanced late sodium current underlies pro-arrhythmic intracellular sodium and calcium dysregulation in murine sodium channelopathy.

Int J Cardiol 2018 07;263:54-62

Heart Center, Department of Clinical and Experimental Cardiology, Academic Medical Center, Meibergdreef 15, 1105AZ Amsterdam, The Netherlands. Electronic address:

Background: Long QT syndrome mutations in the SCN5A gene are associated with an enhanced late sodium current (I) which may lead to pro-arrhythmic action potential prolongation and intracellular calcium dysregulation. We here investigated the dynamic relation between I, intracellular sodium ([Na]) and calcium ([Ca]) homeostasis and pro-arrhythmic events in the setting of a SCN5A mutation.

Methods And Results: Wild-type (WT) and Scn5a (MUT) mice (age 3-5 months) carrying the murine homolog of the SCN5A-1795insD mutation on two distinct genetic backgrounds (FVB/N and 129P2) were studied. [Na], [Ca] and Ca transient amplitude were significantly increased in 129P2-MUT myocytes as compared to WT, but not in FVB/N-MUT. Accordingly, I wassignificantly more enhanced in 129P2-MUT than in FVB/N-MUT myocytes, consistent with a dose-dependent correlation. Quantitative RT-PCR analysis revealed intrinsic differences in mRNA expression levels of the sodium/potassium pump, the sodium/hydrogen exchanger, and sodium‑calcium exchanger between the two mouse strains. The rate of increase in [Na], [Ca] and Ca transient amplitude following the application of the Na/K-ATPase inhibitor ouabain was significantly greater in 129P2-MUT than in 129P2-WT myocytes and was normalized by the I inhibitor ranolazine. Furthermore, ranolazine decreased the incidence of pro-arrhythmic calcium after-transients elicited in 129P2-MUT myocytes.

Conclusions: In this study we established a causal link between the magnitude of I, extent of Na and Ca dysregulation, and incidence of pro-arrhythmic events in murine Scn5a myocytes. Furthermore, our findings provide mechanistic insight into the anti-arrhythmic potential of pharmacological inhibition of I in patients with LQT3 syndrome.
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July 2018

The Brugada Syndrome Susceptibility Gene Modulates Cardiac Transmural Ion Channel Patterning and Electrical Heterogeneity.

Circ Res 2017 Aug 21;121(5):537-548. Epub 2017 Jun 21.

From the Department of Clinical and Experimental Cardiology, Heart Center, Academic Medical Center, Amsterdam, The Netherlands (C.C.V., S.P., R.T., E.M.L., I.M., L.B., A.A.M.W., R.C., A.O.V., C.A.R., C.R.B.); Department of Medicine, Cardiovascular Genetics Center, Montreal Heart Institute, Canada (R.T.); Université de Montréal, Canada (R.T.); Department of Medical Biology, Academic Medical Center, Amsterdam, The Netherlands (B.d.J., R.W., B.J.B., A.O.V.); INSERM, CNRS, Université de Nantes, L'institut du Thorax, Nantes, France (J.B.); Princess Al-Jawhara Al-Brahim Centre of Excellence in Research of Hereditary Disorders, Jeddah, Saudi Arabia (A.A.M.W.); and Electrophysiology and Heart Modeling Institute LIRYC, Université de Bordeaux, France (R.C.).

Rationale: Genome-wide association studies previously identified an association of rs9388451 at chromosome 6q22.3 (near ) with Brugada syndrome. The causal gene and underlying mechanism remain unresolved.

Objective: We used an integrative approach entailing transcriptomic studies in human hearts and electrophysiological studies in ( heterozygous knockout) mice to dissect the underpinnings of the 6q22.31 association with Brugada syndrome.

Methods And Results: We queried expression quantitative trait locus data acquired in 190 human left ventricular samples from the genotype-tissue expression consortium for -expression quantitative trait locus effects of rs9388451, which revealed an association between Brugada syndrome risk allele dosage and expression (β=+0.159; =0.0036). In the same transcriptomic data, we conducted genome-wide coexpression analysis for , which uncovered , encoding the β-subunit of the channel underlying the transient outward current (), as the transcript most robustly correlating with expression (β=+1.47; =2×10). Transcript abundance of and the subunits and , assessed by quantitative reverse transcription-polymerase chain reaction, was higher in subepicardium versus subendocardium in both left and right ventricles, with lower levels in mice compared with wild type. Surface ECG measurements showed less prominent J waves in mice compared with wild-type. In wild-type mice, patch-clamp electrophysiological studies on cardiomyocytes from right ventricle demonstrated a shorter action potential duration and a lower V in subepicardium compared with subendocardium cardiomyocytes, which was paralleled by a higher and a lower sodium current () density in subepicardium versus subendocardium. These transmural differences were diminished in mice because of changes in subepicardial cardiomyocytes.

Conclusions: This study uncovers a role of in the normal transmural electrophysiological gradient in the ventricle and provides compelling evidence that genetic variation at 6q22.31 (rs9388451) is associated with Brugada syndrome through a -dependent alteration of ion channel expression across the cardiac ventricular wall.
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August 2017

Gain-of-function mutation in SCN5A causes ventricular arrhythmias and early onset atrial fibrillation.

Int J Cardiol 2017 Jun 29;236:187-193. Epub 2017 Jan 29.

Heart Center, Department of Clinical and Experimental Cardiology, Academic Medical Center, Amsterdam, The Netherlands. Electronic address:

Background: Mutations in SCN5A, the gene encoding the α-subunit of the cardiac sodium channel (NaV1.5), are associated with a broad spectrum of inherited cardiac arrhythmia disorders. The purpose of this study was to identify the genetic and functional determinants underlying a Dutch family that presented with a combined phenotype of ventricular arrhythmias with a likely adrenergic component, either in isolation or in combination with a mildly decreased heart function and early onset (<55years) atrial fibrillation.

Methods And Results: We performed next generation sequencing in the proband of a two-generation Dutch family and demonstrated a novel missense mutation in SCN5A-(p.M1851V) which co-segregated with the clinical phenotype in the family. We functionally evaluated the putative genetic defect by patch clamp electrophysiological studies in human embryonic kidney cells transfected with mutant or wild-type Nav1.5. The current inactivation was slower and recovery from inactivation was faster in SCN5A-M1851V channels. The voltage dependence of inactivation was shifted towards more positive potentials and consequently, a larger TTX-sensitive window current was observed in SCN5A-M1851V channels. Furthermore, a higher upstroke velocity was observed for the SCN5A-M1851V channels, while the depolarization voltage was more negative, both indicating increased excitability.

Conclusions: This mutation leads to a gain-of-function mechanism based on increased channel availability and increased window current, fitting the observed clinical phenotype of (likely adrenergic-induced) ventricular arrhythmias and atrial fibrillation. These findings further expand the range of cardiac arrhythmias associated with mutations in SCN5A.
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June 2017

Cardiac activation-repolarization patterns and ion channel expression mapping in intact isolated normal human hearts.

Heart Rhythm 2017 02 11;14(2):265-272. Epub 2016 Oct 11.

Cardiology Service, Hospital de la Santa Creu i Sant Pau, IIb Sant Pau, Barcelona, Spain.

Background: The repolarization pattern of the human heart is unknown.

Objective: The purpose of this study was to perform a multisite analysis of the activation-repolarization patterns and mRNA expression patterns of ion channel subunits in isolated human hearts.

Methods: Hearts from 3 donors without reported cardiac disease were Langendorff perfused with the patient's own blood. A standard ECG was obtained before explantation. Up to 92 unipolar electrograms from 24 transmural needles were obtained during right atrial pacing. Local activation and repolarization times and activation-recovery intervals (ARI) were measured. The mRNA levels of subunits of the channels carrying the transient outward current and slow and rapid components of the delayed rectifier current were determined by quantitative reverse transcriptase polymerase chain reaction at up to 63 sites.

Results: The repolarization gradients in the 3 hearts were different and occurred along all axes without midmural late repolarization. A negative activation-repolarization relationship occurred along the epicardium, but this relationship was positive in the whole hearts. Coefficients of variation of mRNA levels (40%-80%) and of the Kv7.1 protein (alpha-subunit slow delayed rectifier channel) were larger than those of ARIs (7%-17%). The regional mRNA expression patterns were similar in the 3 hearts, unlike the ARI profiles. The expression level of individual mRNAs and of Kv7.1 did not correlate with local ARIs at the same sites.

Conclusion: In the normal human heart, repolarization gradients encompass all axes, without late midmural repolarization. Last activated areas do not repolarize first as previously assumed. Gradients of mRNAs of single ion channel subunits and of ARIs do not correlate.
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February 2017

GNB5 Mutations Cause an Autosomal-Recessive Multisystem Syndrome with Sinus Bradycardia and Cognitive Disability.

Am J Hum Genet 2016 09 11;99(3):704-710. Epub 2016 Aug 11.

Medical Genetics Unit, IRCCS Casa Sollievo della Sofferenza, viale Cappuccini, 71013 San Giovanni Rotondo, Foggia, Italy. Electronic address:

GNB5 encodes the G protein β subunit 5 and is involved in inhibitory G protein signaling. Here, we report mutations in GNB5 that are associated with heart-rate disturbance, eye disease, intellectual disability, gastric problems, hypotonia, and seizures in nine individuals from six families. We observed an association between the nature of the variants and clinical severity; individuals with loss-of-function alleles had more severe symptoms, including substantial developmental delay, speech defects, severe hypotonia, pathological gastro-esophageal reflux, retinal disease, and sinus-node dysfunction, whereas related heterozygotes harboring missense variants presented with a clinically milder phenotype. Zebrafish gnb5 knockouts recapitulated the phenotypic spectrum of affected individuals, including cardiac, neurological, and ophthalmological abnormalities, supporting a direct role of GNB5 in the control of heart rate, hypotonia, and vision.
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September 2016

Sudden Cardiac Arrest and Rare Genetic Variants in the Community.

Circ Cardiovasc Genet 2016 Apr 22;9(2):147-53. Epub 2016 Jan 22.

From the Department of Clinical & Experimental Cardiology, Heart Center, Amsterdam Medical Center, University of Amsterdam, Amsterdam, the Netherlands (A.M., M.T.B., E.M.L., D.A.v.H., J.B., T.T.K., A.B., L.B., A.A.M.W., C.R.B., H.L.T.); Institut für Humangenetik, Helmholtz Zentrum München, Munich, Germany; Institut für Humangenetik, Technische Universität München, Munich, Germany (P.L.); Department of Cardiology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands (M.P.v.d.B.); and Princess Al-Jawhara Al-Brahim Centre of Excellence in Research of Hereditary Disorders, Jeddah, Kingdom of Saudi Arabia (A.A.M.W.).

Background: Sudden cardiac arrest (SCA) ranks among the most common causes of death worldwide. Because SCA is most often lethal, yet mostly occurs in individuals without previously known cardiac disease, the identification of patients at risk for SCA could save many lives. In unselected SCA victims from the community, common genetic variants (which are not disease-causing per se, but may increase susceptibility to ventricular fibrillation) are found to be associated with increased SCA risk. However, whether rare genetic variants contribute to SCA risk in the community is largely unexplored.

Methods And Results: We here investigated the involvement of rare genetic variants in SCA risk at the population level by studying the prevalence of 6 founder genetic variants present in the Dutch population (PLN-p.Arg14del, MYBPC3-p.Trp792fsX17, MYBPC3-p.Arg943X, MYBPC3-p.Pro955fsX95, PKP2-p.Arg79X, and the Chr7q36 idiopathic ventricular fibrillation risk haplotype) in a cohort of 1440 unselected Dutch SCA victims included in the Amsterdam Resuscitation Study (ARREST). The six studied founder mutations were found to be more prevalent (1.1%) in the ARREST SCA cohort compared with an ethnically and geographically matched set of controls (0.4%, n=1379; P<0.05) or a set of Dutch individuals drawn from the Genome of the Netherlands (GoNL) study (0%, n=500; P<0.02).

Conclusions: This finding provides proof-of-concept for the notion that rare genetic variants contribute to some extent to SCA risk in the community.
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April 2016

Integrative genomic approach identifies multiple genes involved in cardiac collagen deposition.

Circ Cardiovasc Genet 2014 Dec 12;7(6):790-8. Epub 2014 Sep 12.

From the Department of Experimental Cardiology (E.M.L., B.P.S., L.B., M.E.A., C.R.B.), and Department of Clinical Epidemiology, Biostatistics and Bioinformatics (P.D.M., M.W.T.T.), University of Amsterdam, Academic Medical Center, Amsterdam, Netherlands; and Groningen Bioinformatics Centre, University of Groningen, Groningen, Netherlands (D.A.).

Background: With aging and in cardiac disease, fibrosis caused by collagen deposition is increased, impairing contractility and providing a substrate for arrhythmia. In this study, we set out to identify genetic modifiers of collagen deposition in the heart by exploiting the genetic variability among F2 progeny of 129P2 and FVBN/J mice carrying the Scn5a(tm1Care/+) mutation.

Methods And Results: Relative amounts of collagen were determined in left ventricular myocardium of 65 F2-mice and combined with genome-wide genotypic and cardiac expression data to identify collagen quantitative trait loci (QTLs) and overlapping expression QTLs (eQTLs). A significant collagen QTL was identified on mouse Chr8; an additional collagen QTL was identified on mouse Chr2 after correction for a genetic covariate uncovered on Chr18 using multiple QTL mapping. Of the 24 eQTLs colocalizing with the Chr8-collagen QTL, 6 transcripts were correlated with relative collagen amount. Similarly, of the 7 eQTLs colocalizing with the Chr2-collagen QTL, 1 transcript, Gpr158, correlated with relative collagen. Of the 12 transcripts with an eQTLs in the Chr18-covariate region, only Fgf1 correlated with relative collagen amount. Furthermore, 2 of the transcripts, Pdlim3 (Chr8) and Itga6 (Chr2), with eQTLs overlapping with collagen QTLs, had a genetic covariate on Chr18 that coincided with the Chr18 collagen covariate locus. Application of recombinant human FGF1 to isolated cardiac fibroblasts in culture affected the level of expression of Pdlim3, Itga6, and Gpr158.

Conclusions: We here mapped a possible novel genetic network modulating collagen deposition in mouse left ventricular myocardium.
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December 2014

A mutation in CALM1 encoding calmodulin in familial idiopathic ventricular fibrillation in childhood and adolescence.

J Am Coll Cardiol 2014 Jan 25;63(3):259-66. Epub 2013 Sep 25.

Department of Clinical and Experimental Cardiology, Academic Medical Center, Amsterdam, the Netherlands. Electronic address:

Objectives: This study aimed to identify the genetic defect in a family with idiopathic ventricular fibrillation (IVF) manifesting in childhood and adolescence.

Background: Although sudden cardiac death in the young is rare, it frequently presents as the first clinical manifestation of an underlying inherited arrhythmia syndrome. Gene discovery for IVF is important as it enables the identification of individuals at risk, because except for arrhythmia, IVF does not manifest with identifiable clinical abnormalities.

Methods: Exome sequencing was carried out on 2 family members who were both successfully resuscitated from a cardiac arrest.

Results: We characterized a family presenting with a history of ventricular fibrillation (VF) and sudden death without electrocardiographic or echocardiographic abnormalities at rest. Two siblings died suddenly at the ages of 9 and 10 years, and another 2 were resuscitated from out-of-hospital cardiac arrest with documented VF at ages 10 and 16 years, respectively. Exome sequencing identified a missense mutation affecting a highly conserved residue (p.F90L) in the CALM1 gene encoding calmodulin. This mutation was also carried by 1 of the siblings who died suddenly, from whom DNA was available. The mutation was present in the mother and in another sibling, both asymptomatic but displaying a marginally prolonged QT interval during exercise.

Conclusions: We identified a mutation in CALM1 underlying IVF manifesting in childhood and adolescence. The causality of the mutation is supported by previous studies demonstrating that F90 mediates the direct interaction of CaM with target peptides. Our approach highlights the utility of exome sequencing in uncovering the genetic defect even in families with a small number of affected individuals.
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January 2014

Sudden cardiac arrest associated with use of a non-cardiac drug that reduces cardiac excitability: evidence from bench, bedside, and community.

Eur Heart J 2013 May 20;34(20):1506-16. Epub 2013 Feb 20.

Heart Failure Research Center, University of Amsterdam, Amsterdam, The Netherlands.

Aims: Non-cardiac drugs that impair cardiac repolarization (electrocardiographic QT prolongation) are associated with an increased sudden cardiac arrest (SCA) risk. Emerging evidence suggests that non-cardiac drugs that impair cardiac depolarization and excitability (electrocardiographic QRS prolongation) also increase the risk for SCA. Nortriptyline, which blocks the SCN5A-encoded cardiac sodium channel, may exemplify such drugs. We aimed to study whether nortriptyline increases the risk for SCA, and to establish the underlying mechanisms.

Methods And Results: We studied QRS durations during rest/exercise in an index patient who experienced ventricular tachycardia during exercise while using nortriptyline, and compared them with those of 55 controls with/without nortriptyline and 24 controls with Brugada syndrome (BrS) without nortriptyline, who carried an SCN5A mutation. We performed molecular-genetic (exon-trapping) and functional (patch-clamp) experiments to unravel the mechanisms of QRS prolongation by nortriptyline and the SCN5A mutation found in the index patient. We conducted a prospective community-based study among 944 victims of ECG-documented SCA and 4354-matched controls to determine the risk for SCA associated with nortriptyline use. Multiple mechanisms may act in concert to increase the risk for SCA during nortriptyline use. Pharmacological (nortriptyline), genetic (loss-of-function SCN5A mutation), and/or functional (sodium channel inactivation at fast heart rates) factors conspire to reduce the cardiac sodium current and increase the risk for SCA. Nortriptyline use in the community was associated with a 4.5-fold increase in the risk for SCA [adjusted OR: 4.5 (95% CI: 1.1-19.5)], particularly when other sodium channel-blocking factors were present.

Conclusions: Nortriptyline increases the risk for SCA in the general population, particularly in the presence of genetic and/or non-genetic factors that decrease cardiac excitability by blocking the cardiac sodium channel.
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May 2013

Intercalated disc abnormalities, reduced Na(+) current density, and conduction slowing in desmoglein-2 mutant mice prior to cardiomyopathic changes.

Cardiovasc Res 2012 Sep 3;95(4):409-18. Epub 2012 Jul 3.

Department of Cardiac, Thoracic and Vascular Sciences, University of Padua, Padua 35121, Italy.

Aims: Mutations in genes encoding desmosomal proteins have been implicated in the pathogenesis of arrhythmogenic right ventricular cardiomyopathy (ARVC). However, the consequences of these mutations in early disease stages are unknown. We investigated whether mutation-induced intercalated disc remodelling impacts on electrophysiological properties before the onset of cell death and replacement fibrosis.

Methods And Results: Transgenic mice with cardiac overexpression of mutant Desmoglein2 (Dsg2) Dsg2-N271S (Tg-NS/L) were studied before and after the onset of cell death and replacement fibrosis. Mice with cardiac overexpression of wild-type Dsg2 and wild-type mice served as controls. Assessment by electron microscopy established that intercellular space widening at the desmosomes/adherens junctions occurred in Tg-NS/L mice before the onset of necrosis and fibrosis. At this stage, epicardial mapping in Langendorff-perfused hearts demonstrated prolonged ventricular activation time, reduced longitudinal and transversal conduction velocities, and increased arrhythmia inducibility. A reduced action potential (AP) upstroke velocity due to a lower Na(+) current density was also observed at this stage of the disease. Furthermore, co-immunoprecipitation demonstrated an in vivo interaction between Dsg2 and the Na(+) channel protein Na(V)1.5.

Conclusion: Intercellular space widening at the level of the intercalated disc (desmosomes/adherens junctions) and a concomitant reduction in AP upstroke velocity as a consequence of lower Na(+) current density lead to slowed conduction and increased arrhythmia susceptibility at disease stages preceding the onset of necrosis and replacement fibrosis. The demonstration of an in vivo interaction between Dsg2 and Na(V)1.5 provides a molecular pathway for the observed electrical disturbances during the early ARVC stages.
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September 2012

Electrophysiologic remodeling of the left ventricle in pressure overload-induced right ventricular failure.

J Am Coll Cardiol 2012 Jun;59(24):2193-202

Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Meibergdreef 9, Amsterdam, the Netherlands.

Objectives: The purpose of this study was to analyze the electrophysiologic remodeling of the atrophic left ventricle (LV) in right ventricular (RV) failure (RVF) after RV pressure overload.

Background: The LV in pressure-induced RVF develops dysfunction, reduction in mass, and altered gene expression, due to atrophic remodeling. LV atrophy is associated with electrophysiologic remodeling.

Methods: We conducted epicardial mapping in Langendorff-perfused hearts, patch-clamp studies, gene expression studies, and protein level studies of the LV in rats with pressure-induced RVF (monocrotaline [MCT] injection, n = 25; controls with saline injection, n = 18). We also performed epicardial mapping of the LV in patients with RVF after chronic thromboembolic pulmonary hypertension (CTEPH) (RVF, n = 10; no RVF, n = 16).

Results: The LV of rats with MCT-induced RVF exhibited electrophysiologic remodeling: longer action potentials (APs) at 90% repolarization and effective refractory periods (ERPs) (60 ± 1 ms vs. 44 ± 1 ms; p < 0.001), and slower longitudinal conduction velocity (62 ± 2 cm/s vs. 70 ± 1 cm/s; p = 0.003). AP/ERP prolongation agreed with reduced Kcnip2 expression, which encodes the repolarizing potassium channel subunit KChIP2 (0.07 ± 0.01 vs. 0.11 ± 0.02; p < 0.05). Conduction slowing was not explained by impaired impulse formation, as AP maximum upstroke velocity, whole-cell sodium current magnitude/properties, and mRNA levels of Scn5a were unaltered. Instead, impulse transmission in RVF was hampered by reduction in cell length (111.6 ± 0.7 μm vs. 122.0 ± 0.4 μm; p = 0.02) and width (21.9 ± 0.2 μm vs. 25.3 ± 0.3 μm; p = 0.002), and impaired cell-to-cell impulse transmission (24% reduction in Connexin-43 levels). The LV of patients with CTEPH with RVF also exhibited ERP prolongation (306 ± 8 ms vs. 268 ± 5 ms; p = 0.001) and conduction slowing (53 ± 3 cm/s vs. 64 ± 3 cm/s; p = 0.005).

Conclusions: Pressure-induced RVF is associated with electrophysiologic remodeling of the atrophic LV.
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June 2012

A complex double deletion in LMNA underlies progressive cardiac conduction disease, atrial arrhythmias, and sudden death.

Circ Cardiovasc Genet 2011 Jun 15;4(3):280-7. Epub 2011 Mar 15.

Heart Failure Research Center, Department of Experimental Cardiology, Amsterdam, The Netherlands.

Background: Cardiac conduction disease is a clinically and genetically heterogeneous disorder characterized by defects in electrical impulse generation and conduction and is associated with sudden cardiac death.

Methods And Results: We studied a 4-generation family with autosomal dominant progressive cardiac conduction disease, including atrioventricular conduction block and sinus bradycardia, atrial arrhythmias, and sudden death. Genome-wide linkage analysis mapped the disease locus to chromosome 1p22-q21. Multiplex ligation-dependent probe amplification analysis of the LMNA gene, which encodes the nuclear-envelope protein lamin A/C, revealed a novel gene rearrangement involving a 24-bp inversion flanked by a 3.8-kb deletion upstream and a 7.8-kb deletion downstream. The presence of short inverted sequence homologies at the breakpoint junctions suggested a mutational event involving serial replication slippage in trans during DNA replication.

Conclusions: We identified for the first time a complex LMNA gene rearrangement involving a double deletion in a 4-generation Dutch family with progressive conduction system disease. Our findings underscore the fact that if conventional polymerase chain reaction-based direct sequencing approaches for LMNA analysis are negative in suggestive pedigrees, mutation detection techniques capable of detecting gross genomic lesions involving deletions and insertions should be considered.
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June 2011

Right ventricular failure following chronic pressure overload is associated with reduction in left ventricular mass: evidence for atrophic remodeling.

J Am Coll Cardiol 2011 Feb;57(8):921-8

Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.

Objectives: We sought to study whether patients with right ventricular failure (RVF) secondary to chronic thromboembolic pulmonary hypertension (CTEPH) have reduced left ventricular (LV) mass, and whether LV mass reduction is caused by atrophy.

Background: The LV in patients with CTEPH is underfilled (unloaded). LV unloading may cause atrophic remodeling that is associated with diastolic and systolic dysfunction.

Methods: We studied LV mass using cardiac magnetic resonance imaging (MRI) in 36 consecutive CTEPH patients (before/after pulmonary endarterectomy [PEA]) and 11 healthy volunteers selected to match age and sex of patients. We studied whether LV atrophy is present in monocrotaline (MCT)-injected rats with RVF or controls by measuring myocyte dimensions and performing in situ hybridization.

Results: At baseline, CTEPH patients with RVF had significantly lower LV free wall mass indexes than patients without RVF (35 ± 6 g/m(2) vs. 44 ± 7 g/m(2), p = 0.007) or volunteers (42 ± 6 g/m(2), p = 0.006). After PEA, LV free wall mass index increased (from 38 ± 6 g/m(2) to 44 ± 9 g/m(2), p = 0.001), as right ventricular (RV) ejection fraction improved (from 31 ± 8% to 56 ± 12%, p < 0.001). Compared with controls, rats with RVF had reduced LV free wall mass and smaller LV free wall myocytes. Expression of atrial natriuretic peptide was higher, whereas that of α-myosin heavy chain and sarcoplasmic reticulum calcium ATPase-2 were lower in RVF than in controls, both in RV and LV.

Conclusions: RVF in patients with CTEPH is associated with reversible reduction in LV free wall mass. In a rat model of RVF, myocyte shrinkage due to atrophic remodeling contributed to reduction in LV free wall mass.
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February 2011

Quantitative trait loci for electrocardiographic parameters and arrhythmia in the mouse.

J Mol Cell Cardiol 2011 Mar 18;50(3):380-9. Epub 2010 Sep 18.

Heart Failure Research Center, Department of Experimental Cardiology, University of Amsterdam, Amsterdam, The Netherlands.

Cardiac arrhythmias associated with sudden death are influenced by multiple biological pathways and are modulated by numerous genetic and environmental factors. Elevated heart rate and prolonged ECG indices of conduction and repolarization have been associated with risk of sudden death. Insight into the genetic underpinnings of these parameters thus provides an important means to the dissection of the genetic components modulating risk of sudden cardiac death. In this study we mapped quantitative trait loci (QTL) modulating heart rate, ECG indices of conduction and repolarization, and susceptibility to arrhythmia, in a conduction disease-sensitized F(2) mouse population. Heart rate, P-duration, PR-, QRS- and QT-interval were measured at baseline (n=502) and after flecainide administration (n=370) in mutant F(2) progeny (F(2)-MUT) resulting from the FVB/NJ-Scn5a1798(insD/+) X 129P2-Scn5a1798(insD/+) mouse cross. Episodes of sinus arrhythmia and ventricular tachyarrhythmia occurring post-flecainide were treated as binary traits. F(2)-MUT mice were genotyped using a genome-wide 768 single nucleotide polymorphism (SNP) panel. Interval mapping uncovered multiple QTL for ECG parameters and arrhythmia. A sex-interacting scan identified QTL displaying sex-dependency, and a two-dimensional QTL scan unmasked locus-locus (epistasis) interactions influencing ECG traits. A number of QTL coincided at specific chromosomal locations, suggesting pleiotropic effects at these loci. Through transcript profiling in myocardium from the parental mouse strains we identified genes co-localizing at the identified QTL that constitute highly relevant candidates for the observed effects. The detection of QTL influencing ECG indices and arrhythmia is an essential step towards identifying genetic networks for sudden, arrhythmic, cardiac death.
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March 2011

Mechanism of right precordial ST-segment elevation in structural heart disease: excitation failure by current-to-load mismatch.

Heart Rhythm 2010 12;7(2):238-48. Epub 2009 Oct 12.

Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.

Background: The Brugada sign has been associated with mutations in SCN5A and with right ventricular structural abnormalities. Their role in the Brugada sign and the associated ventricular arrhythmias is unknown.

Objective: The purpose of this study was to delineate the role of structural abnormalities and sodium channel dysfunction in the Brugada sign.

Methods: Activation and repolarization characteristics of the explanted heart of a patient with a loss-of-function mutation in SCN5A (G752R) and dilated cardiomyopathy were determined after induction of right-sided ST-segment elevation by ajmaline. In addition, right ventricular structural discontinuities and sodium channel dysfunction were simulated in a computer model encompassing the heart and thorax.

Results: In the explanted heart, disappearance of local activation in unipolar electrograms at the basal right ventricular epicardium was followed by monophasic ST-segment elevation. The local origin of this phenomenon was confirmed by coaxial electrograms. Neither early repolarization nor late activation correlated with ST-segment elevation. At sites of local ST-segment elevation, the subepicardium was interspersed with adipose tissue and contained more fibrous tissue than either the left ventricle or control hearts. In computer simulations entailing right ventricular structural discontinuities, reduction of sodium channel conductance or size of the gaps between introduced barriers resulted in subepicardial excitation failure or delayed activation by current-to-load mismatch and in the Brugada sign on the ECG.

Conclusion: Right ventricular excitation failure and activation delay by current-to-load mismatch in the subepicardium can cause the Brugada sign. Therefore, current-to-load mismatch may underlie the ventricular arrhythmias in patients with the Brugada sign.
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May 2010

Genetically determined differences in sodium current characteristics modulate conduction disease severity in mice with cardiac sodium channelopathy.

Circ Res 2009 Jun 30;104(11):1283-92. Epub 2009 Apr 30.

Heart Failure Research Center, Department of Experimental Cardiology, Academic Medical Center, University of Amsterdam, Room K2-110, PO Box 22700, 1100 DE Amsterdam, The Netherlands.

Conduction slowing of the electric impulse that drives the heartbeat may evoke lethal cardiac arrhythmias. Mutations in SCN5A, which encodes the pore-forming cardiac sodium channel alpha subunit, are associated with familial arrhythmia syndromes based on conduction slowing. However, disease severity among mutation carriers is highly variable. We hypothesized that genetic modifiers underlie the variability in conduction slowing and disease severity. With the aim of identifying such modifiers, we studied the Scn5a(1798insD/+) mutation in 2 distinct mouse strains, FVB/N and 129P2. In 129P2 mice, the mutation resulted in more severe conduction slowing particularly in the right ventricle (RV) compared to FVB/N. Pan-genomic mRNA expression profiling in the 2 mouse strains uncovered a drastic reduction in mRNA encoding the sodium channel auxiliary subunit beta4 (Scn4b) in 129P2 mice compared to FVB/N. This corresponded to low to undetectable beta4 protein levels in 129P2 ventricular tissue, whereas abundant beta4 protein was detected in FVB/N. Sodium current measurements in isolated myocytes from the 2 mouse strains indicated that sodium channel activation in myocytes from 129P2 mice occurred at more positive potentials compared to FVB/N. Using computer simulations, this difference in activation kinetics was predicted to explain the observed differences in conduction disease severity between the 2 strains. In conclusion, genetically determined differences in sodium current characteristics on the myocyte level modulate disease severity in cardiac sodium channelopathies. In particular, the sodium channel subunit beta4 (SCN4B) may constitute a potential genetic modifier of conduction and cardiac sodium channel disease.
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June 2009

Haplotype-sharing analysis implicates chromosome 7q36 harboring DPP6 in familial idiopathic ventricular fibrillation.

Am J Hum Genet 2009 Apr 12;84(4):468-76. Epub 2009 Mar 12.

Department of Clinical Genetics, Academic Medical Center, Amsterdam, The Netherlands.

Idiopathic Ventricular Fibrillation (IVF) is defined as spontaneous VF without any known structural or electrical heart disease. A family history is present in up to 20% of probands with the disorder, suggesting that at least a subset of IVF is hereditary. A genome-wide haplotype-sharing analysis was performed for identification of the responsible gene in three distantly related families in which multiple individuals died suddenly or were successfully resuscitated at young age. We identified a haplotype, on chromosome 7q36, that was conserved in these three families and was also shared by 7 of 42 independent IVF patients. The shared chromosomal segment harbors part of the DPP6 gene, which encodes a putative component of the transient outward current in the heart. We demonstrated a 20-fold increase in DPP6 mRNA levels in the myocardium of carriers as compared to controls. Clinical evaluation of 84 risk-haplotype carriers and 71 noncarriers revealed no ECG or structural parameters indicative of cardiac disease. Penetrance of IVF was high; 50% of risk-haplotype carriers experienced (aborted) sudden cardiac death before the age of 58 years. We propose DPP6 as a gene for IVF and increased DPP6 expression as the likely pathogenetic mechanism.
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April 2009

Exclusion of multiple candidate genes and large genomic rearrangements in SCN5A in a Dutch Brugada syndrome cohort.

Heart Rhythm 2007 Jun 2;4(6):752-5. Epub 2007 Mar 2.

Center for Heart Failure Research, Experimental and Molecular Cardiology Group, University of Amsterdam, Amsterdam, The Netherlands.

Background: The Brugada syndrome is an inherited cardiac electrical disorder associated with a high incidence of life-threatening arrhythmias. Screening for mutations in the cardiac Na+ channel-encoding gene SCN5A uncovers a mutation in approximately 20% of Brugada syndrome cases. Genetic heterogeneity and/or undetected SCN5A mutations, such as exon duplications and deletions, could be involved in the remaining 80% mutation-negative patients.

Objectives: Thirty-eight SCN5A mutation-negative Dutch Brugada syndrome probands were studied. The SCN5A gene was investigated for exon duplication and deletion, and a number of candidate genes (Caveolin-3, Irx-3, Irx-4, Irx-5, Irx-6, Plakoglobin, Plakophilin-2, SCN1B, SCN2B, SCN3B, and SCN4B) were tested for the occurrence of point mutations and small insertions/deletions.

Methods: We used a quantitative multiplex approach to determine SCN5A exon copy numbers. Mutation analysis of the candidate genes was performed by direct sequencing of polymerase chain reaction-amplified coding regions.

Results: No large genomic rearrangements in SCN5A were identified. No mutations were found in the candidate genes. Twenty novel polymorphisms were identified in these genes.

Conclusion: Large genomic rearrangements in SCN5A are not a common cause of Brugada syndrome. Similarly, the studied candidate genes are unlikely to be major causal genes of Brugada syndrome. Further studies are required to identify other genes responsible for this syndrome.
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June 2007

Role of sequence variations in the human ether-a-go-go-related gene (HERG, KCNH2) in the Brugada syndrome.

Cardiovasc Res 2005 Dec 25;68(3):441-53. Epub 2005 Jul 25.

Department of Experimental Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.

Background: Brugada syndrome (BrS) is an inherited electrical disorder associated with a high incidence of sudden death. In a minority of patients, it has been linked to mutations in SCN5A, the gene encoding the pore-forming alpha-subunit of the cardiac Na(+) channel. Other causally related genes still await identification. We evaluated the role of HERG (KCNH2), which encodes the alpha-subunit of the rapid delayed rectifier K(+) channel (I(Kr)), in BrS.

Methods And Results: In two unrelated SCN5A mutation-negative patients, different amino acid changes in the C-terminal domain of the HERG channel (G873S and N985S) were identified. Voltage-clamp experiments on transfected HEK-293 cells show that these changes increase I(Kr) density and cause a negative shift of voltage-dependent inactivation, resulting in increased rectification. Action potential (AP) clamp experiments reveal increased transient HERG peak currents (I(peak)) during phase-0 and phase-1 of the ventricular AP, particularly at short cycle length. Computer simulations demonstrate that the increased I(peak) enhances the susceptibility to loss of the AP-dome typically in right ventricular subepicardial myocytes, thereby contributing to the BrS phenotype.

Conclusion: Our study reveals a modulatory role of I(Kr) in BrS. These findings may provide better understanding of BrS and have implications for diagnosis and therapy.
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December 2005