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Abstract
With recent advances in genetic diagnostics, many inherited diseases, which can cause life-threatening arrhythmias, are being better characterized. Many of these diseases are caused by genetic disorders that affect the function of the ion channels that regulate the action potential or the function of important cardiac muscle regulatory proteins. This article summarizes the diseases that we have learned about, such as the long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia. The article examines the diagnosis, genetic screening of patients and their relatives, management, and referral to a specialist for further therapy.
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Affiliation(s)
- Jessica Kline
- Cardiovascular Disease, Summa Health System, 95 Arch Street, Suite 300, Akron, OH 44304, USA
| | - Otto Costantini
- Cardiovascular Disease Fellowship, Summa Health Heart and Vascular Institute, Summa Health System, 95 Arch Street, Suite 350, Akron, OH 44304, USA.
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Han D, Tan H, Sun C, Li G. Dysfunctional Nav1.5 channels due to SCN5A mutations. Exp Biol Med (Maywood) 2018; 243:852-863. [PMID: 29806494 DOI: 10.1177/1535370218777972] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The voltage-gated sodium channel 1.5 (Nav1.5), encoded by the SCN5A gene, is responsible for the rising phase of the action potential of cardiomyocytes. The sodium current mediated by Nav1.5 consists of peak and late components (INa-P and INa-L). Mutant Nav1.5 causes alterations in the peak and late sodium current and is associated with an increasingly wide range of congenital arrhythmias. More than 400 mutations have been identified in the SCN5A gene. Although the mechanisms of SCN5A mutations leading to a variety of arrhythmias can be classified according to the alteration of INa-P and INa-L as gain-of-function, loss-of-function and both, few researchers have summarized the mechanisms in this way before. In this review article, we aim to review the mechanisms underlying dysfunctional Nav1.5 due to SCN5A mutations and to provide some new insights into further approaches in the treatment of arrhythmias. Impact statement The field of ion channelopathy caused by dysfunctional Nav1.5 due to SCN5A mutations is rapidly evolving as novel technologies of electrophysiology are introduced and our understanding of the mechanisms of various arrhythmias develops. In this review, we focus on the dysfunctional Nav1.5 related to arrhythmias and the underlying mechanisms. We update SCN5A mutations in a precise way since 2013 and presents novel classifications of SCN5A mutations responsible for the dysfunction of the peak (INa-P) and late (INa-L) sodium channels based on their phenotypes, including loss-, gain-, and coexistence of gain- and loss-of function mutations in INa-P, INa-L, respectively. We hope this review will provide a new comprehensive way to better understand the electrophysiological mechanisms underlying arrhythmias from cell to bedside, promoting the management of various arrhythmias in practice.
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Affiliation(s)
- Dan Han
- 1 Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an 710061, P.R. China
| | - Hui Tan
- 2 Department of Respiratory Medicine, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an 710061, P.R. China
| | - Chaofeng Sun
- 1 Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an 710061, P.R. China
| | - Guoliang Li
- 1 Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an 710061, P.R. China
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Kochenov АV, Poddubnaya YP, Makedonsky IA, Korogod SМ. Excitability Characteristics of a Urinary Bladder Detrusor Smooth Muscle Cell as a Basis for Choosing Parameters of Rehabilitation Electrostimulation: A Simulation Study. NEUROPHYSIOLOGY+ 2015. [DOI: 10.1007/s11062-015-9504-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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van Hoeijen DA, Blom MT, Tan HL. Cardiac sodium channels and inherited electrophysiological disorders: an update on the pharmacotherapy. Expert Opin Pharmacother 2014; 15:1875-87. [PMID: 24992280 DOI: 10.1517/14656566.2014.936380] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
INTRODUCTION Since the recognition of inherited sodium (Na(+)) channel disease, the cardiac Na(+) channel has been extensively studied. Both loss-of-function and gain-of-function mutations of the cardiac Na(+) channel are associated with cardiac arrhythmia and sudden cardiac death. Pathophysiological mechanisms that may induce arrhythmia are unravelled and include alterations in biophysical properties due to the mutation in SCN5A, drug use and circumstantial factors. Insights into the mechanisms of inherited Na(+) channel disease may result in tailored therapy. However, due to the complexity of cardiac electrical activity and pathophysiological mechanisms, pharmacotherapy in cardiac Na(+) channel disease remains challenging. AREAS COVERED This review discusses various mechanisms involved in inherited Na(+) channel disorders, focussing on Brugada syndrome (Brs) and long QT syndrome type 3 (LQTS3). It aims to provide an overview of developments in pharmacotherapy, discussing both treatment and which drugs to avoid to prevent arrhythmia. EXPERT OPINION Altered biophysical properties of cardiac Na(+) channels are the basis of arrhythmias in patients with inherited Na(+) channel diseases such as BrS and LQTS3. The effects of such biophysical derangements are strongly modulated by concomitant factors. Tailored drug therapy is required to prevent arrhythmia and is best achieved by educating patients affected by Na(+) channel disorders.
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Affiliation(s)
- Daniel A van Hoeijen
- University of Amsterdam, Academic Medical Center, Department of Cardiology , P.O. Box 22660, 1100 DD, Amsterdam , The Netherlands +0031 20 566 3264 ; +0031 20 566 9131 ;
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Bébarová M. Arrhythmogenesis in Brugada syndrome: impact and constrains of current concepts. Int J Cardiol 2013; 167:1760-71. [PMID: 23295036 DOI: 10.1016/j.ijcard.2012.12.019] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Revised: 11/15/2012] [Accepted: 12/06/2012] [Indexed: 01/13/2023]
Abstract
Brugada syndrome (BrS), an inherited arrhythmogenic disease first described in 1992, is characterized by ST segment elevations on the electrocardiogram in the right precordium and by a high occurrence of arrhythmias including the life-threatening ventricular tachycardia/fibrillation. Knowledge of the underlying mechanisms of formation of arrhythmogenic substrate in BrS is essential, namely for the risk stratification of BrS patients and their therapy which is still restrained almost exclusively to the implantation of cardioverter/defibrillator. In spite of many crucial findings in this field published within recent years, the final consistent view has not been established so far. Hence, BrS described 20 years ago remains an actual topic of both clinical and experimental studies. This review presents an overview of the current knowledge related to the pathogenesis of BrS arrhythmogenic substrate, namely of the genetic basis of BrS, functional consequences of mutations related to BrS, and arrhythmogenic mechanisms in BrS.
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Affiliation(s)
- Markéta Bébarová
- Department of Physiology, Faculty of Medicine, Masaryk University, Kamenice 5, 625 00 Brno, Bohunice, Czech Republic.
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Savio-Galimberti E, Gollob MH, Darbar D. Voltage-gated sodium channels: biophysics, pharmacology, and related channelopathies. Front Pharmacol 2012; 3:124. [PMID: 22798951 PMCID: PMC3394224 DOI: 10.3389/fphar.2012.00124] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2011] [Accepted: 06/11/2012] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated sodium channels (VGSC) are multi-molecular protein complexes expressed in both excitable and non-excitable cells. They are primarily formed by a pore-forming multi-spanning integral membrane glycoprotein (α-subunit) that can be associated with one or more regulatory β-subunits. The latter are single-span integral membrane proteins that modulate the sodium current (INa) and can also function as cell adhesion molecules. In vitro some of the cell-adhesive functions of the β-subunits may play important physiological roles independently of the α-subunits. Other endogenous regulatory proteins named “channel partners” or “channel interacting proteins” (ChiPs) like caveolin-3 and calmodulin/calmodulin kinase II (CaMKII) can also interact and modulate the expression and/or function of VGSC. In addition to their physiological roles in cell excitability and cell adhesion, VGSC are the site of action of toxins (like tetrodotoxin and saxitoxin), and pharmacologic agents (like antiarrhythmic drugs, local anesthetics, antiepileptic drugs, and newly developed analgesics). Mutations in genes that encode α- and/or β-subunits as well as the ChiPs can affect the structure and biophysical properties of VGSC, leading to the development of diseases termed sodium “channelopathies”. This review will outline the structure, function, and biophysical properties of VGSC as well as their pharmacology and associated channelopathies and highlight some of the recent advances in this field.
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Affiliation(s)
- Eleonora Savio-Galimberti
- Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University Nashville, TN, USA
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Kim AS, Huffer L. Atrial Fibrillation and Brugada Syndrome. Card Electrophysiol Clin 2012; 4:249-257. [PMID: 26939822 DOI: 10.1016/j.ccep.2012.02.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Since its first description in 1992, the Brugada syndrome (BrS) has attracted significant attention from the cardiology community because of its association with malignant ventricular arrhythmias and sudden cardiac death. Supraventricular tachyarrhythmias in BrS represent a unique and seemingly higher-risk clinical subgroup of patients with BrS. Atrial fibrillation represents the most common supraventricular arrhythmia in patients with BrS, with average ranges reported in the literature of 20% to 40%. This article summarizes the current literature regarding the patient with BrS with atrial fibrillation and discusses the management of these clinically challenging and potentially higher-risk individuals.
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Affiliation(s)
- Andrew S Kim
- Cardiology Service, Department of Medicine, Walter Reed National Military Medical Center, 8901 Rockville Pike, Bethesda, MD 20889, USA
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Wilde AA, Brugada R. Phenotypical Manifestations of Mutations in the Genes Encoding Subunits of the Cardiac Sodium Channel. Circ Res 2011; 108:884-97. [DOI: 10.1161/circresaha.110.238469] [Citation(s) in RCA: 171] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Arthur A.M. Wilde
- From the Heart Research Centre (A.A.M.W.), Department of Clinical and Experimental Cardiology, Academic Medical Center, University Medical Center, University of Amsterdam, The Netherlands; and the Institut d'Investigació Biomèdica Girona-IdIBGi (R.B.), Universitat de Girona, Giona Spain
| | - Ramon Brugada
- From the Heart Research Centre (A.A.M.W.), Department of Clinical and Experimental Cardiology, Academic Medical Center, University Medical Center, University of Amsterdam, The Netherlands; and the Institut d'Investigació Biomèdica Girona-IdIBGi (R.B.), Universitat de Girona, Giona Spain
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Nishii N, Ogawa M, Morita H, Nakamura K, Banba K, Miura D, Kumagai N, Matsunaga A, Kawamura H, Urakawa S, Miyaji K, Nagai M, Satoh K, Nakagawa K, Tanaka M, Hiramatsu S, Tada T, Murakami M, Nagase S, Kohno K, Kusano KF, Saku K, Ohe T, Ito H. SCN5A mutation is associated with early and frequent recurrence of ventricular fibrillation in patients with Brugada syndrome. Circ J 2010; 74:2572-8. [PMID: 21048329 DOI: 10.1253/circj.cj-10-0445] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND Mutations in SCN5A are reportedly linked to Brugada syndrome (BS), but recent observations suggest that they are not necessarily associated with ventricular fibrillation (VF) in BS patients. Therefore, the clinical importance of SCN5A mutations in BS patients was examined in the present study. METHODS AND RESULTS The 108 BS patients were examined for SCN5A mutations and various parameters were compared between patients with and without mutations. An implantable cardioverter defibrillator (ICD) was implanted in 49 patients and a predictor of appropriate ICD shock was investigated. The existence of a SCN5A mutation was not associated with initial VF episodes (21.7% vs 20.0%, P=0.373). In the secondary prevention group, appropriate shock-free survival rate was significantly lower in patients with spontaneous type 1 ECG than in those without (41.1% vs 85.7% at 2 years, P=0.014). The appropriate shock-free survival rate was also significantly lower in patients with SCN5A mutations than in those without (28.6% vs 83.3% at 1 year, P=0.040). Appropriate shock was more frequent in patients with SCN5A mutations than in those without (6.6±6.2 vs 1.7±3.0, P=0.007). CONCLUSIONS SCN5A mutations are associated with early and frequent VF recurrence, but not with initial VF episodes. This is the first report on the genotype-phenotype interaction and clinical significance of this mutation.
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Affiliation(s)
- Nobuhiro Nishii
- Department of Cardiovascular Medicine, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan.
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Wilde AAM, Postema PG, Di Diego JM, Viskin S, Morita H, Fish JM, Antzelevitch C. The pathophysiological mechanism underlying Brugada syndrome: depolarization versus repolarization. J Mol Cell Cardiol 2010; 49:543-53. [PMID: 20659475 DOI: 10.1016/j.yjmcc.2010.07.012] [Citation(s) in RCA: 253] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2010] [Revised: 07/13/2010] [Accepted: 07/19/2010] [Indexed: 12/29/2022]
Abstract
This Point/Counterpoint presents a scholarly debate of the mechanisms underlying the electrocardiographic and arrhythmic manifestations of Brugada syndrome (BrS), exploring in detail the available evidence in support of the repolarization vs. depolarization hypothesis.
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Affiliation(s)
- Arthur A M Wilde
- Department of Cardiology, Academic Medical Center Amsterdam, Amsterdam, The Netherlands
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Casini S, Tan HL, Demirayak I, Remme CA, Amin AS, Scicluna BP, Chatyan H, Ruijter JM, Bezzina CR, van Ginneken ACG, Veldkamp MW. Tubulin polymerization modifies cardiac sodium channel expression and gating. Cardiovasc Res 2009; 85:691-700. [PMID: 19861310 DOI: 10.1093/cvr/cvp352] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
AIMS Treatment with the anticancer drug taxol (TXL), which polymerizes the cytoskeleton protein tubulin, may evoke cardiac arrhythmias based on reduced human cardiac sodium channel (Na(v)1.5) function. Therefore, we investigated whether enhanced tubulin polymerization by TXL affects Na(v)1.5 function and expression and whether these effects are beta1-subunit-mediated. METHODS AND RESULTS Human embryonic kidney (HEK293) cells, transfected with SCN5A cDNA alone (Na(v)1.5) or together with SCN1B cDNA (Na(v)1.5 + beta1), and neonatal rat cardiomyocytes (NRCs) were incubated in the presence and in the absence of 100 microM TXL. Sodium current (I(Na)) characteristics were studied using patch-clamp techniques. Na(v)1.5 membrane expression was determined by immunocytochemistry and confocal microscopy. Pre-treatment with TXL reduced peak I(Na) amplitude nearly two-fold in both Na(v)1.5 and Na(v)1.5 + beta1, as well as in NRCs, compared with untreated cells. Accordingly, HEK293 cells and NRCs stained with anti-Na(v)1.5 antibody revealed a reduced membrane-labelling intensity in the TXL-treated groups. In addition, TXL accelerated I(Na) decay of Na(v)1.5 + beta1, whereas I(Na) decay of Na(v)1.5 remained unaltered. Finally, TXL reduced the fraction of channels that slow inactivated from 31% to 18%, and increased the time constant of slow inactivation by two-fold in Na(v)1.5. Conversely, slow inactivation properties of Na(v)1.5 + beta1 were unchanged by TXL. CONCLUSION Enhanced tubulin polymerization reduces sarcolemmal Na(v)1.5 expression and I(Na) amplitude in a beta1-subunit-independent fashion and causes I(Na) fast and slow inactivation impairment in a beta1-subunit-dependent way. These changes may underlie conduction-slowing-dependent cardiac arrhythmias under conditions of enhanced tubulin polymerization, e.g. TXL treatment and heart failure.
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Affiliation(s)
- Simona Casini
- Department of Clinical and Experimental Cardiology, Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands
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Atrial standstill associated with loss of atrial myocytes: A rare cause of fetal bradyarrhythmia. Heart Rhythm 2009; 6:1370-2. [DOI: 10.1016/j.hrthm.2009.04.026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Accepted: 04/20/2009] [Indexed: 11/19/2022]
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Gargus JJ. Genetic calcium signaling abnormalities in the central nervous system: seizures, migraine, and autism. Ann N Y Acad Sci 2009; 1151:133-56. [PMID: 19154521 DOI: 10.1111/j.1749-6632.2008.03572.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The calcium ion is one of the most versatile, ancient, and universal of biological signaling molecules, known to regulate physiological systems at every level from membrane potential and ion transporters to kinases and transcription factors. Disruptions of intracellular calcium homeostasis underlie a host of emerging diseases, the calciumopathies. Cytosolic calcium signals originate either as extracellular calcium enters through plasma membrane ion channels or from the release of an intracellular store in the endoplasmic reticulum (ER) via inositol triphosphate receptor and ryanodine receptor channels. Therefore, to a large extent, calciumopathies represent a subset of the channelopathies, but include regulatory pathways and the mitochondria, the major intracellular calcium repository that dynamically participates with the ER stores in calcium signaling, thereby integrating cellular energy metabolism into these pathways, a process of emerging importance in the analysis of the neurodegenerative and neuropsychiatric diseases. Many of the calciumopathies are common complex polygenic diseases, but leads to their understanding come most prominently from rare monogenic channelopathy paradigms. Monogenic forms of common neuronal disease phenotypes-such as seizures, ataxia, and migraine-produce a constitutionally hyperexcitable tissue that is susceptible to periodic decompensations. The gene families and genetic lesions underlying familial hemiplegic migraine, FHM1/CACNA1A, FHM2/ATP1A2, and FHM3/SCN1A, and monogenic mitochondrial migraine syndromes, provide a robust platform from which genes, such as CACNA1C, which encodes the calcium channel mutated in Timothy syndrome, can be evaluated for their role in autism and bipolar disease.
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Affiliation(s)
- J Jay Gargus
- Department of Physiology & Biophysics, Section of Human Genetics, School of Medicine, University of California-Irvine, Irvine, CA 92697, USA.
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Abstract
The Brugada syndrome, first described as a new clinical entity in 1992, is widely recognized today as a form of inherited sudden cardiac arrest. The past 16 years witnessed a progressive increase in the number of reported cases and a dramatic proliferation of articles serving to define the clinical, genetic, cellular, ionic, and molecular aspects of the disease. This article provides a brief overview of recent advances in our understanding of the clinical presentation and molecular and cellular mechanisms and an update of existing controversies.
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Meregalli PG, Tan HL, Probst V, Koopmann TT, Tanck MW, Bhuiyan ZA, Sacher F, Kyndt F, Schott JJ, Albuisson J, Mabo P, Bezzina CR, Le Marec H, Wilde AAM. Type of SCN5A mutation determines clinical severity and degree of conduction slowing in loss-of-function sodium channelopathies. Heart Rhythm 2008; 6:341-8. [PMID: 19251209 DOI: 10.1016/j.hrthm.2008.11.009] [Citation(s) in RCA: 162] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2008] [Accepted: 11/07/2008] [Indexed: 11/25/2022]
Abstract
BACKGROUND Patients carrying loss-of-function SCN5A mutations linked to Brugada syndrome (BrS) or progressive cardiac conduction disease (PCCD) are at risk of sudden cardiac death at a young age. The penetrance and expressivity of the disease are highly variable, and new tools for risk stratification are needed. OBJECTIVES We aimed to establish whether the type of SCN5A mutation correlates with the clinical and electrocardiographic phenotype. METHODS We studied BrS or PCCD probands and their relatives who carried a SCN5A mutation. Mutations were divided into 2 main groups: missense mutations (M) or mutations leading to premature truncation of the protein (T). The M group was subdivided according to available biophysical properties: M mutations with <or=90% (M(active)) or >90% (M(inactive)) peak I(Na) reduction were analyzed separately. RESULTS The study group was composed of 147 individuals with 32 different mutations. No differences in age and sex distribution were found between the groups. Subjects carrying a T mutation had significantly more syncopes than those with an M(active) mutation (19 of 75 versus 2 of 35, P = .03). Also, mutations associated with drastic peak I(Na) reduction (T and M(inactive) mutants) had a significantly longer PR interval, compared with M(active) mutations. All other electrocardiographic parameters were comparable. After drug provocation testing, both PR and QRS intervals were significantly longer in the T and M(inactive) groups than in the M(active) group. CONCLUSION In loss-of-function SCN5A channelopathies, patients carrying T and M(inactive) mutations develop a more severe phenotype than those with M(active) mutations. This is associated with more severe conduction disorders. This is the first time that genetic data are proposed for risk stratification in BrS.
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Affiliation(s)
- Paola G Meregalli
- Department of Cardiology, Academic Medical Centre, University of Amsterdam, Amsterdam, the Netherlands
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SCN5A channelopathies--an update on mutations and mechanisms. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 98:120-36. [PMID: 19027780 DOI: 10.1016/j.pbiomolbio.2008.10.005] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Voltage-gated Na+ channels mediate the rapid upstroke of the action potential in excitable tissues. Na(v)1.5, encoded by the SCN5A gene, is the predominant isoform in the heart. Mutations in SCN5A are associated with distinct cardiac excitation disorders often resulting in life-threatening arrhythmias. This review outlines the currently known SCN5A mutations linked to three distinct cardiac rhythm disorders: long QT syndrome subtype 3 (LQT3), Brugada syndrome (BS), and cardiac conduction disease (CCD). Electrophysiological properties of the mutant channels are summarized and discussed in terms of Na+ channel structure-function relationships and regarding molecular mechanisms underlying the respective cardiac dysfunction. Possible reasons for less convincing genotype-phenotype correlations are suggested.
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Lin MT, Wu MH, Chang CC, Chiu SN, Thériault O, Huang H, Christé G, Ficker E, Chahine M. In utero onset of long QT syndrome with atrioventricular block and spontaneous or lidocaine-induced ventricular tachycardia: compound effects of hERG pore region mutation and SCN5A N-terminus variant. Heart Rhythm 2008; 5:1567-74. [PMID: 18848812 DOI: 10.1016/j.hrthm.2008.08.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2008] [Accepted: 08/08/2008] [Indexed: 02/07/2023]
Abstract
BACKGROUND Mexiletine may protect patients with long QT syndrome (LQTS) type 3 from arrhythmias. However, we found an unusual in utero presentation of intermittent atrioventricular block and ventricular tachycardia (spontaneous or lidocaine-induced) in a fetus and his sibling with LQTS. OBJECTIVE The purpose of this study was to investigate the underlying channelopathy and functional alteration. METHODS Mutations were searched in KCNQ1, HERG, KCNE1, KCNE2, and SCN5A genes. In expressed mutants, whole-cell voltage clamp defined the electrophysiologic properties. RESULTS Novel missense mutations involving hERG (F627L) at the pore region and SCN5A (R43Q) at the N-terminus were found in the proband and in family members with prolonged QT interval. In oocytes injected with mRNA encoding hERG/ F627L, almost zero K(+) currents were elicited. In coinjected oocytes, the currents were decreased to half. In tsA201 cells transfected with SCN5A/R43Q, although the baseline kinetics of the Na current were similar to wild type, lidocaine caused a unique hyperpolarizing shift of the activation and increased the availability of Na currents at resting voltages. Window currents were enhanced due to a right shift of steady-state inactivation. These electrophysiologic alterations after lidocaine may lead to the development of ventricular tachycardia. CONCLUSION We identified a novel hERG/F627L mutation that results in LQTS with fetal onset of atrioventricular block and ventricular tachycardia. A coexisting SCN5A/R43Q variant, although it per se does not prolong repolarization, contributes to the development of ventricular tachyarrhythmias after lidocaine. Patients with such latent lidocaine-induced phenotype who are given lidocaine or mexiletine may be at risk.
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Affiliation(s)
- Ming-Tai Lin
- Department of Pediatrics, National Taiwan University Hospital and College of Medicine, National Taiwan University, Taipei, Taiwan
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Shi R, Zhang Y, Yang C, Huang C, Zhou X, Qiang H, Grace AA, Huang CLH, Ma A. The cardiac sodium channel mutation delQKP 1507-1509 is associated with the expanding phenotypic spectrum of LQT3, conduction disorder, dilated cardiomyopathy, and high incidence of youth sudden death. Europace 2008; 10:1329-35. [PMID: 18697752 PMCID: PMC2573028 DOI: 10.1093/europace/eun202] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Aim We report diverse phenotypic consequences of the delQKP-1507–1509 cardiac sodium channel mutation in three generations of a Chinese family. Methods and results Clinical and electrocardiographic (ECG), echocardiographic examination was followed by direct sequencing of SCN5A, KCNQ1, HERG, and LAMIN A/C to screen genomic DNA from blood samples. Of two mutation carriers, the proband was born with conduction disorders including second-degree atrioventricular (AV) block with prolonged QTc interval, additionally showing left anterior fascicular block (LAFB), incomplete right bundle-branch block (IRBBB), and intermittent third-degree AV block at 2 years, and clinical presentations of multiple syncope despite normal electroencephalograms at 8 years. Continuous ECG monitoring following presentation at 13 years revealed prolonged QTc and biphasic T-waves, multiple episodes of ventricular tachycardia, ventricular fibrillation, and torsades de pointes. Transthoracal echocardiography then revealed left ventricular dilatation and reduced systolic function. Another mutation carrier showed features of long QT syndrome type 3 (LQT3), LAFB, and dilated cardiomyopathy (DCM). Two additional subjects died suddenly at 13 and 33 years. Conclusion This data compliments and expands the spectrum of phenotypes resulting from this known gain-of-function mutation, including not only LQT3, cardiac conduction defects, and sudden death but also DCM, hitherto associated with loss-of-function mutations, for the first time.
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Affiliation(s)
- Ruiming Shi
- 1Department of Paediatrics, First Affiliated Hospital, Cardiovascular Ion Channel Disease Laboratory, Medical College of Xi'an Jiaotong University, Xi'an, Peoples Republic of China
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Cordeiro JM, Mazza M, Goodrow R, Ulahannan N, Antzelevitch C, Di Diego JM. Functionally distinct sodium channels in ventricular epicardial and endocardial cells contribute to a greater sensitivity of the epicardium to electrical depression. Am J Physiol Heart Circ Physiol 2008; 295:H154-62. [PMID: 18456729 DOI: 10.1152/ajpheart.01327.2007] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A greater depression of the action potential (AP) of the ventricular epicardium (Epi) versus endocardium (Endo) is readily observed in experimental models of acute ischemia and Brugada syndrome. Endo and Epi differences in transient outward K(+) current and/or ATP-sensitive K(+) channel current are believed to contribute to the differential response. The present study tested the hypothesis that the greater sensitivity of Epi is due in part to its functionally distinct early fast Na(+) current (I(Na)). APs were recorded from isolated Epi and Endo tissue slices and coronary-perfused wedge preparations before and after exposures to elevated extracellular K(+) concentration ([K(+)](o); 6-12 mM). I(Na) was recorded from Epi and Endo myocytes using whole cell patch-clamp techniques. In tissue slices, increasing [K(+)](o) to 12 mM reduced V(max) to 51.1 +/- 5.3% and 26.8 +/- 9.6% of control in Endo (n = 9) and Epi (n = 14), respectively (P < 0.05). In wedge preparations (n = 12), the increase in [K(+)](o) caused selective depression of Epi APs and transmural conduction slowing and block. I(Na) density was not significantly different between Epi (n = 14) and Endo (n = 15) cells, but Epi cells displayed a more negative half-inactivation voltage [-83.6 +/- 0.1 and -75.5 +/- 0.3 mV for Epi (n = 16) and Endo (n = 16), respectively, P < 0.05]. Our data suggest that reduced I(Na) availability in ventricular Epi may contribute to its greater sensitivity to electrical depression and thus may contribute to the R-ST segment changes observed under a variety of clinical conditions including acute myocardial ischemia, severe hyperkalemia, and Brugada syndrome.
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Affiliation(s)
- J M Cordeiro
- Masonic Medical Research Laboratory, Utica, NY 13504, USA
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Atrial fibrillation and Brugada syndrome. J Am Coll Cardiol 2008; 51:1149-53. [PMID: 18355651 DOI: 10.1016/j.jacc.2007.10.062] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2007] [Revised: 10/19/2007] [Accepted: 10/29/2007] [Indexed: 11/24/2022]
Abstract
Brugada syndrome is characterized by right bundle branch block pattern with ST-segment elevation in leads V(1) to V(3) and a propensity for sudden cardiac death due to ventricular arrhythmias. The arrhythmogenic substrate in Brugada syndrome may not be restricted to the ventricles, and atrial arrhythmias are being increasingly reported. Incidences of spontaneous atrial arrhythmias vary from 6% to 38% and those of inducible atrial arrhythmias from 3% to 100%. Atrial fibrillation (AF) is the most common atrial arrhythmia found in Brugada syndrome. Enhanced duration of atrial action potential and increased intra-atrial conduction time may contribute to the genesis of atrial arrhythmias in Brugada syndrome. Atrial arrhythmias are an important cause of inappropriate discharge of implantable defibrillators in patients with Brugada syndrome. Hence, implantation of dual-chamber defibrillators and careful programming of single-chamber devices have been recommended. Atrial fibrillation has been associated with mutations in both the sodium and calcium channels of the heart, as well as with cases of Brugada syndrome that could not genotyped to any of the known genes associated with the disease. This observation suggests that the substrate responsible for the development of ventricular arrhythmias also may contribute to arrhythmogenesis in the atria of the heart. The presence of a prominent transient outward current in atria and the observation that episodes of AF are triggered by closely coupled atrial extrasystoles point to the possibility that a substrate similar to that responsible for ventricular arrhythmogenesis underlies the development of AF in patients with Brugada syndrome.
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Smits JPP, Blom MT, Wilde AAM, Tan HL. Cardiac sodium channels and inherited electrophysiologic disorders: a pharmacogenetic overview. Expert Opin Pharmacother 2008; 9:537-49. [DOI: 10.1517/14656566.9.4.537] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Arab S, Liu PP, Emili A. Lost in translation: five grand challenges for proteomic biomarker discovery. EXPERT OPINION ON MEDICAL DIAGNOSTICS 2007; 1:325-336. [PMID: 23489353 DOI: 10.1517/17530059.1.3.325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The biomedical community has the imperative to develop reliable, clinically relevant and generalizable bioassays that can be used to accurately recognize those individuals with early-stage disease or those patients who will respond to therapy, with the ultimate aim of achieving individualized medicine. In recent years, increasingly sophisticated proteomic screening technologies have been introduced, providing the biomedical community with a valuable new approach for the systematic discovery and validation of novel diagnostic, prognostic and therapeutic tools. Nevertheless, the complexity of the cellular milieu wherein a variety of macromolecules interact in dynamic fashion, combined with the complex clinical manifestation of chronic pathologies and widespread diversity of patient populations, mean that universal biomarkers will not be easily developed. In this review, the five key challenges that must be surmounted in order to advance the clinical impact of this nascent field are described, and plausible solutions based on the authors' own ongoing proteomic profiling of cardiovascular disease is outlined.
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Affiliation(s)
- Sara Arab
- University of Toronto, Toronto General Hospital, 610 University Avenue, Toronto, Ontario, M5G 2M9, Canada
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Gautier M, Zhang H, Fearon IM. Peroxynitrite formation mediates LPC-induced augmentation of cardiac late sodium currents. J Mol Cell Cardiol 2007; 44:241-51. [PMID: 17961592 DOI: 10.1016/j.yjmcc.2007.09.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2007] [Revised: 08/31/2007] [Accepted: 09/10/2007] [Indexed: 12/17/2022]
Abstract
Lysophosphatidylcholine (LPC) accumulates in the ischaemic myocardium and is arrhythmogenic. We have examined the mechanisms underlying the effects of LPC on the late cardiac Na(+) current (I(L)Na). Na(+) currents were recorded in HEK293 cells expressing Na(V)1.5 and isolated rat ventricular myocytes. LPC enhanced recombinant I(L)Na, while it reduced peak Na(+) current. Computer modeling of human ventricular myocyte action potentials predicted a marked duration prolonging effect and arrhythmogenic potential due to these effects of LPC on peak and late currents. Enhancement of recombinant I(L)Na was suppressed by the antioxidant ascorbic acid and by the NADPH oxidase inhibitor DPI. Inhibitors of the mitochondrial electron transport chain (rotenone, TTFA and myxothiazol) were without effect on LPC responses. The superoxide donor pyrogallol was without effect on I(L)Na. Enhancement of I(L)Na was abrogated by the NOS inhibitors l-NAME and 7-nitroindazole, while LPC induced an l-NAME-sensitive production of NO, measured as enhanced DAF-FM fluorescence, in both HEK293 cells and ventricular myocytes. Despite this, the NO donors SNAP and SNP caused no change in I(L)Na. However, SNAP enhanced TTX-sensitive recombinant and native I(L)Na in the presence of pyrogallol, suggesting peroxynitrite formation as a mediator of the response to LPC. In support of this, the peroxynitrite scavenger FeTPPS prevented the response of I(L)Na to LPC. Peroxynitrite formation provides a novel mechanism by which LPC regulates the late cardiac Na(+) current.
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Affiliation(s)
- Mathieu Gautier
- Faculty of Life Sciences, The University of Manchester, Floor 2, Core Technology Facility, 46 Grafton Street, Manchester, M13 9NT, UK
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Grandi E, Puglisi JL, Wagner S, Maier LS, Severi S, Bers DM. Simulation of Ca-calmodulin-dependent protein kinase II on rabbit ventricular myocyte ion currents and action potentials. Biophys J 2007; 93:3835-47. [PMID: 17704163 PMCID: PMC2084250 DOI: 10.1529/biophysj.107.114868] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Ca-calmodulin-dependent protein kinase II (CaMKII) was recently shown to alter Na(+) channel gating and recapitulate a human Na(+) channel genetic mutation that causes an unusual combined arrhythmogenic phenotype in patients: simultaneous long QT syndrome and Brugada syndrome. CaMKII is upregulated in heart failure where arrhythmias are common, and CaMKII inhibition can reduce arrhythmias. Thus, CaMKII-dependent channel modulation may contribute to acquired arrhythmic disease. We developed a Markovian Na(+) channel model including CaMKII-dependent changes, and incorporated it into a comprehensive myocyte action potential (AP) model with Na(+) and Ca(2+) transport. CaMKII shifts Na(+) current (I(Na)) availability to more negative voltage, enhances intermediate inactivation, and slows recovery from inactivation (all loss-of-function effects), but also enhances late noninactivating I(Na) (gain of function). At slow heart rates, with long diastolic time for I(Na) recovery, late I(Na) is the predominant effect, leading to AP prolongation (long QT syndrome). At fast heart rates, where recovery time is limited and APs are shorter, there is little effect on AP duration, but reduced availability decreases I(Na), AP upstroke velocity, and conduction (Brugada syndrome). CaMKII also increases cardiac Ca(2+) and K(+) currents (I(Ca) and I(to)), complicating CaMKII-dependent AP changes. Incorporating I(Ca) and I(to) effects individually prolongs and shortens AP duration. Combining I(Na), I(Ca), and I(to) effects results in shortening of AP duration with CaMKII. With transmural heterogeneity of I(to) and I(to) downregulation in heart failure, CaMKII may accentuate dispersion of repolarization. This provides a useful initial framework to consider pathways by which CaMKII may contribute to arrhythmogenesis.
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Affiliation(s)
- Eleonora Grandi
- Biomedical Engineering Laboratory, Department of Electronics, Computer Science and Systems, University of Bologna, Bologna, Italy
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Jespersen T, Gavillet B, van Bemmelen MX, Cordonier S, Thomas MA, Staub O, Abriel H. Cardiac sodium channel Na(v)1.5 interacts with and is regulated by the protein tyrosine phosphatase PTPH1. Biochem Biophys Res Commun 2006; 348:1455-62. [PMID: 16930557 DOI: 10.1016/j.bbrc.2006.08.014] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2006] [Accepted: 08/04/2006] [Indexed: 10/24/2022]
Abstract
In order to identify proteins interacting with the cardiac voltage-gated sodium channel Na(v)1.5, we used the last 66 amino acids of the C-terminus of the channel as bait to screen a human cardiac cDNA library. We identified the protein tyrosine phosphatase PTPH1 as an interacting protein. Pull-down experiments confirmed the interaction, and indicated that it depends on the PDZ-domain binding motif of Na(v)1.5. Co-expression experiments in HEK293 cells showed that PTPH1 shifts the Na(v)1.5 availability relationship toward hyperpolarized potentials, whereas an inactive PTPH1 or the tyrosine kinase Fyn does the opposite. The results of this study suggest that tyrosine phosphorylation destabilizes the inactivated state of Na(v)1.5.
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Affiliation(s)
- Thomas Jespersen
- Department of Pharmacology and Toxicology, University of Lausanne, Switzerland
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