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Osorio LA, Lozano M, Soto P, Moreno-Hidalgo V, Arévalo-Gil A, Ramírez-Balaguera A, Hevia D, Cifuentes J, Hidalgo Y, Alcayaga-Miranda F, Pasten C, Morales D, Varela D, Urquidi C, Iturriaga A, Rivera-Palma A, Larrea-Gómez R, Irarrázabal CE. Levels of Small Extracellular Vesicles Containing hERG-1 and Hsp47 as Potential Biomarkers for Cardiovascular Diseases. Int J Mol Sci 2024; 25:4913. [PMID: 38732154 PMCID: PMC11084293 DOI: 10.3390/ijms25094913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2024] [Revised: 04/03/2024] [Accepted: 04/07/2024] [Indexed: 05/13/2024] Open
Abstract
The diagnosis of cardiovascular disease (CVD) is still limited. Therefore, this study demonstrates the presence of human ether-a-go-go-related gene 1 (hERG1) and heat shock protein 47 (Hsp47) on the surface of small extracellular vesicles (sEVs) in human peripheral blood and their association with CVD. In this research, 20 individuals with heart failure and 26 participants subjected to cardiac stress tests were enrolled. The associations between hERG1 and/or Hsp47 in sEVs and CVD were established using Western blot, flow cytometry, electron microscopy, ELISA, and nanoparticle tracking analysis. The results show that hERG1 and Hsp47 were present in sEV membranes, extravesicularly exposing the sequences 430AFLLKETEEGPPATE445 for hERG1 and 169ALQSINEWAAQTT- DGKLPEVTKDVERTD196 for Hsp47. In addition, upon exposure to hypoxia, rat primary cardiomyocytes released sEVs into the media, and human cardiomyocytes in culture also released sEVs containing hERG1 (EV-hERG1) and/or Hsp47 (EV-Hsp47). Moreover, the levels of sEVs increased in the blood when cardiac ischemia was induced during the stress test, as well as the concentrations of EV-hERG1 and EV-Hsp47. Additionally, the plasma levels of EV-hERG1 and EV-Hsp47 decreased in patients with decompensated heart failure (DHF). Our data provide the first evidence that hERG1 and Hsp47 are present in the membranes of sEVs derived from the human cardiomyocyte cell line, and also in those isolated from human peripheral blood. Total sEVs, EV-hERG1, and EV-Hsp47 may be explored as biomarkers for heart diseases such as heart failure and cardiac ischemia.
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Affiliation(s)
- Luis A. Osorio
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
| | - Mauricio Lozano
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
| | - Paola Soto
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
| | - Viviana Moreno-Hidalgo
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
| | - Angely Arévalo-Gil
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
| | - Angie Ramírez-Balaguera
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
| | - Daniel Hevia
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
| | - Jorge Cifuentes
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
| | - Yessia Hidalgo
- Laboratory of Nano-Regenerative Medicine, Center of Interventional Medicine for Precision and Advanced Cellular Therapy (IMPACT), Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile
| | - Francisca Alcayaga-Miranda
- Laboratory of Nano-Regenerative Medicine, Center of Interventional Medicine for Precision and Advanced Cellular Therapy (IMPACT), Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile
| | - Consuelo Pasten
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
- Faculty of Medicine, Universidad de los Andes, Santiago 7620001, Chile
| | - Danna Morales
- Faculty of Medicine, Universidad de Chile, Santiago 8380453, Chile
| | - Diego Varela
- Faculty of Medicine, Universidad de Chile, Santiago 8380453, Chile
| | - Cinthya Urquidi
- Department of Epidemiology and Health Studies, Facultad de Medicina, Universidad de los Andes, Santiago 7620001, Chile
| | - Andrés Iturriaga
- Departamento de Matemática y Ciencia de la Computación, Facultad de Ciencia, Universidad de Santiago de Chile, Santiago 9170020, Chile
| | | | | | - Carlos E. Irarrázabal
- Laboratory of Molecular and Integrative Physiology, Physiology Program, Centro de Investigación e Innovación Biomédica (CiiB), Universidad de los Andes, Santiago 7620001, Chile; (L.A.O.); (C.P.)
- Faculty of Medicine, Universidad de los Andes, Santiago 7620001, Chile
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Cheng YJ, Wu Y, Wei HQ, Liao YJ, Qu LP, Pan YH, Liu LJ, Bi WT. A novel mutation in hERG gene associated with azithromycin-induced acquired long QT syndrome. Mol Biol Rep 2024; 51:520. [PMID: 38625436 DOI: 10.1007/s11033-024-09421-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Accepted: 03/06/2024] [Indexed: 04/17/2024]
Abstract
BACKGROUND Mutations in human ether-à-go-go-related gene (hERG) potassium channels are closely associated with long QT syndrome (LQTS). Previous studies have demonstrated that macrolide antibiotics increase the risk of cardiovascular diseases. To date, the mechanisms underlying acquired LQTS remain elusive. METHODS A novel hERG mutation I1025N was identified in an azithromycin-treated patient with acquired long QT syndrome via Sanger sequencing. The mutant I1025N plasmid was transfected into HEK-293 cells, which were subsequently incubated with azithromycin. The effect of azithromycin and mutant I1025N on the hERG channel was evaluated via western blot, immunofluorescence, and electrophysiology techniques. RESULTS The protein expression of the mature hERG protein was down-regulated, whereas that of the immature hERG protein was up-regulated in mutant I1025N HEK-293 cells. Azithromycin administration resulted in a negative effect on the maturation of the hERG protein. Additionally, the I1025N mutation exerted an inhibitory effect on hERG channel current. Moreover, azithromycin inhibited hERG channel current in a concentration-dependent manner. The I1025N mutation and azithromycin synergistically decreased hERG channel expression and hERG current. However, the I1025N mutation and azithromycin did not alter channel gating dynamics. CONCLUSIONS These findings suggest that hERG gene mutations might be involved in the genetic susceptibility mechanism underlying acquired LQTS induced by azithromycin.
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Affiliation(s)
- Yun-Jiu Cheng
- Department of Guangdong Cardiovascular Institute, Guangdong Provincial People's Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, Guangzhou, China
- The Second School of Clinical Medicine, Southern Medical University, Guangzhou, China
| | - Yang Wu
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
- NHC Key Laboratory of Assisted Circulation and Vascular Diseases, Sun Yat-sen University, Guangzhou, China
| | - Hui-Qiang Wei
- Department of Guangdong Cardiovascular Institute, Guangdong Provincial People's Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, Guangzhou, China
| | - Yi-Jian Liao
- The First Clinical Medical College, Guangdong Medical University, Zhanjiang, China
| | - Li-Ping Qu
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
- NHC Key Laboratory of Assisted Circulation and Vascular Diseases, Sun Yat-sen University, Guangzhou, China
| | - Yue-Han Pan
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
- NHC Key Laboratory of Assisted Circulation and Vascular Diseases, Sun Yat-sen University, Guangzhou, China
| | - Li-Juan Liu
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
- NHC Key Laboratory of Assisted Circulation and Vascular Diseases, Sun Yat-sen University, Guangzhou, China.
| | - Wen-Tao Bi
- Department of Cardiovascular Medicine, People's Hospital of Macheng City, Macheng, China.
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A Case Series of Concomitant Cardiac Electrical Disease among Takotsubo Syndrome Patients and Literature Review. J Cardiovasc Dev Dis 2022; 9:jcdd9030079. [PMID: 35323627 PMCID: PMC8955983 DOI: 10.3390/jcdd9030079] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Revised: 02/21/2022] [Accepted: 03/01/2022] [Indexed: 01/06/2023] Open
Abstract
The pathophysiology of Takotsubo Syndrome (TTS) is not completely understood and the trigger of sudden cardiac death (SCD) in TTS is not clear either. We therefore sought to find an association between TTS and primary electrical diseases. A total of 148 TTS patients were analyzed between 2003 and 2017 in a bi-centric manner. Additionally, a literature review was performed. The patients were included in an ongoing retrospective cohort database. The coexistence of TTS and primary electrical diseases was confirmed in five cases as the following: catecholaminergic polymorphic ventricular tachycardia (CPVT, 18-year-old female) (n = 1), LQTS 1 (72-year-old female and 65-year-old female) (n = 2), LQTS 2 (17-year-old female) (n = 1), and LQTS in the absence of mutations (22-year-old female). Four patients suffered from malignant tachyarrhythmia and recurrent syncope after TTS. Except for the CPVT patient and one LQTS 1 patient, all other cases underwent subcutaneous ICD implantation. An event recorder of the CPVT patient after starting beta-blocker did not detect arrhythmias. The diagnosis of primary electrical disease was in 80% of cases unmasked on a TTS event. This diagnosis triggered a family clinical and genetic screening confirming the diagnosis of primary electrical disease. A subsequent literature review identified five cases as the following: a congenital atrioventricular block (n = 1), a Jervell and Lange-Nielsen Syndrome (n = 1), and a family LQTS in the absence of a mutation (n = 2), LQTS 2 (n = 1). A primary electrical disease should be suspected in young and old TTS patients with a family history of sudden cardiac death. In suspected cases, e.g., ongoing QT interval prolongation, despite recovery of left ventricular ejection fraction a family screening is recommended.
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Tse G, Li KHC, Cheung CKY, Letsas KP, Bhardwaj A, Sawant AC, Liu T, Yan GX, Zhang H, Jeevaratnam K, Sayed N, Cheng SH, Wong WT. Arrhythmogenic Mechanisms in Hypokalaemia: Insights From Pre-clinical Models. Front Cardiovasc Med 2021; 8:620539. [PMID: 33614751 PMCID: PMC7887296 DOI: 10.3389/fcvm.2021.620539] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 01/13/2021] [Indexed: 12/21/2022] Open
Abstract
Potassium is the predominant intracellular cation, with its extracellular concentrations maintained between 3. 5 and 5 mM. Among the different potassium disorders, hypokalaemia is a common clinical condition that increases the risk of life-threatening ventricular arrhythmias. This review aims to consolidate pre-clinical findings on the electrophysiological mechanisms underlying hypokalaemia-induced arrhythmogenicity. Both triggers and substrates are required for the induction and maintenance of ventricular arrhythmias. Triggered activity can arise from either early afterdepolarizations (EADs) or delayed afterdepolarizations (DADs). Action potential duration (APD) prolongation can predispose to EADs, whereas intracellular Ca2+ overload can cause both EADs and DADs. Substrates on the other hand can either be static or dynamic. Static substrates include action potential triangulation, non-uniform APD prolongation, abnormal transmural repolarization gradients, reduced conduction velocity (CV), shortened effective refractory period (ERP), reduced excitation wavelength (CV × ERP) and increased critical intervals for re-excitation (APD-ERP). In contrast, dynamic substrates comprise increased amplitude of APD alternans, steeper APD restitution gradients, transient reversal of transmural repolarization gradients and impaired depolarization-repolarization coupling. The following review article will summarize the molecular mechanisms that generate these electrophysiological abnormalities and subsequent arrhythmogenesis.
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Affiliation(s)
- Gary Tse
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin, China.,Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom
| | - Ka Hou Christien Li
- Faculty of Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom
| | | | - Konstantinos P Letsas
- Second Department of Cardiology, Laboratory of Cardiac Electrophysiology, Evangelismos General Hospital of Athens, Athens, Greece
| | - Aishwarya Bhardwaj
- Division of Cardiology, Department of Internal Medicine, State University of New York at Buffalo, Buffalo, NY, United States
| | - Abhishek C Sawant
- Division of Cardiology, Department of Internal Medicine, State University of New York at Buffalo, Buffalo, NY, United States
| | - Tong Liu
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin, China
| | - Gan-Xin Yan
- Lankenau Institute for Medical Research and Lankenau Medical Center, Wynnewood, PA, United States
| | - Henggui Zhang
- School of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom
| | - Kamalan Jeevaratnam
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom
| | - Nazish Sayed
- Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA, United States.,Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA, United States.,Department of Medicine, Division of Cardiology, Stanford University School of Medicine, Stanford, CA, United States
| | - Shuk Han Cheng
- Department of Biomedical Sciences, College of Veterinary Medicine and Life Science, City University of Hong Kong, Hong Kong, China.,State Key Laboratory of Marine Pollution (SKLMP), City University of Hong Kong, Hong Kong, China.,Department of Materials Science and Engineering, College of Science and Engineering, City University of Hong Kong, Hong Kong, China
| | - Wing Tak Wong
- School of Life Sciences, Chinese University of Hong Kong, Hong Kong, China
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5
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Wolf F, Homiedi M, Elias M, Freedberg N, Goldstein LH. Does infection prolong the QT interval? Intern Med J 2020; 50:1078-1084. [DOI: 10.1111/imj.14741] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Revised: 12/19/2019] [Accepted: 12/28/2019] [Indexed: 01/08/2023]
Affiliation(s)
- Frieda Wolf
- Internal Medicine C Emek Medical Center Afula Iran
| | | | - Mazen Elias
- Internal Medicine C Emek Medical Center Afula Iran
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6
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Pro-arrhythmic effects of low plasma [K +] in human ventricle: An illustrated review. Trends Cardiovasc Med 2017; 28:233-242. [PMID: 29203397 DOI: 10.1016/j.tcm.2017.11.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Revised: 10/18/2017] [Accepted: 11/05/2017] [Indexed: 12/25/2022]
Abstract
Potassium levels in the plasma, [K+]o, are regulated precisely under physiological conditions. However, increases (from approx. 4.5 to 8.0mM) can occur as a consequence of, e.g., endurance exercise, ischemic insult or kidney failure. This hyperkalemic modulation of ventricular electrophysiology has been studied extensively. Hypokalemia is also common. It can occur in response to diuretic therapy, following renal dialysis, or during recovery from endurance exercise. In the human ventricle, clinical hypokalemia (e.g., [K+]o levels of approx. 3.0mM) can cause marked changes in both the resting potential and the action potential waveform, and these may promote arrhythmias. Here, we provide essential background information concerning the main K+-sensitive ion channel mechanisms that act in concert to produce prominent short-term ventricular electrophysiological changes, and illustrate these by implementing recent mathematical models of the human ventricular action potential. Even small changes (~1mM) in [K+]o result in significant alterations in two different K+ currents, IK1 and HERG. These changes can markedly alter in resting membrane potential and/or action potential waveform in human ventricle. Specifically, a reduction in net outward transmembrane K+ currents (repolarization reserve) and an increased substrate input resistance contribute to electrophysiological instability during the plateau of the action potential and may promote pro-arrhythmic early after-depolarizations (EADs). Translational settings where these insights apply include: optimal diuretic therapy, and the interpretation of data from Phase II and III trials for anti-arrhythmic drug candidates.
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7
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Fujii Y, Matsumoto Y, Hayashi K, Ding WG, Tomita Y, Fukumoto D, Wada Y, Ichikawa M, Sonoda K, Ozawa J, Makiyama T, Ohno S, Yamagishi M, Matsuura H, Horie M, Itoh H. Contribution of a KCNH2 variant in genotyped long QT syndrome: Romano–Ward syndrome under double mutations and acquired long QT syndrome under heterozygote. J Cardiol 2017; 70:74-79. [DOI: 10.1016/j.jjcc.2016.09.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Revised: 09/09/2016] [Accepted: 09/23/2016] [Indexed: 01/08/2023]
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8
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Omar A, Zhou M, Berman A, Sorrentino RA, Yar N, Weintraub NL, Kim IM, Lei W, Tang Y. Genomic-based diagnosis of arrhythmia disease in a personalized medicine era. EXPERT REVIEW OF PRECISION MEDICINE AND DRUG DEVELOPMENT 2016; 1:497-504. [PMID: 28944294 PMCID: PMC5606339 DOI: 10.1080/23808993.2016.1264258] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
INTRODUCTION Although thousands of potentially disease-causing mutations have been identified in a handful of genes, the genetic heterogeneity has led to diagnostic confusions, stemming directly from the limitations in our arsenal of genetic tools. AREAS COVERED We discuss the genetic basis of cardiac ion channelopathies, the gaps in our knowledge and how Next-generation sequencing technology (NGS) and can be used to bridge them, and how induced pluripotent stem cell (iPSC) derived-cardiomyocytes can be used for drug discovery. EXPERT COMMENTARY Univariate, arrhythmogenic arrhythmias can explain some congenital arrhythmias, however, it is far from a comprehensive understanding of the complexity of many arrhythmias. Mutational screening is a critical step in personalized medicine and is critical to the management of patients with arrhythmias. The success of personalized medicine requires a more efficient way to identify a high number of genetic variants potentially implicated in cardiac arrhythmogenic diseases than traditional sequencing methods (eg, Sanger sequencing). Next-generation sequencing technology provides us with unprecedented opportunities to achieve high-throughput, rapid, and cost-effective detection of congenital arrhythmias in patients. Moreover, in personalized medicine era, IPSC derived-cardiomyocytes can be used as 'cardiac arrhythmia in a dish' model for drug discovery, and help us improve management of arrhythmias in patients by developing patient-specific drug therapies with target specificity.
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Affiliation(s)
- Abdullah Omar
- Department of Medicine, Medical College of Georgia, Augusta University, Augusta, GA, USA
| | - Mi Zhou
- Cardiac Surgery department, Ruijin Hospital, Shanghai Jiao Tong University, Shanghai, China
| | - Adam Berman
- Department of Medicine, Medical College of Georgia, Augusta University, Augusta, GA, USA
| | - Robert A. Sorrentino
- Department of Medicine, Medical College of Georgia, Augusta University, Augusta, GA, USA
| | - Neela Yar
- Purdue University, West Lafayette, IN, USA
| | - Neal L. Weintraub
- Department of Medicine, Medical College of Georgia, Augusta University, Augusta, GA, USA
| | - Il-man Kim
- Department of Medicine, Medical College of Georgia, Augusta University, Augusta, GA, USA
| | - Wei Lei
- Cardiovascular Medicine Center, Affiliated Hospital of Guangdong Medical University, Zhanjiang, China
| | - Yaoliang Tang
- Department of Medicine, Medical College of Georgia, Augusta University, Augusta, GA, USA
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9
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El‐Battrawy I, Behnes M, Borggrefe M, Akin I. Association of a congenital long QT syndrome type 1 with Takotsubo cardiomyopathy. Clin Case Rep 2016; 4:789-92. [PMID: 27525086 PMCID: PMC4974430 DOI: 10.1002/ccr3.567] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2015] [Revised: 03/17/2016] [Accepted: 04/03/2016] [Indexed: 11/07/2022] Open
Abstract
The occurrence of takotsubo cardiomyopathy in a patient with congenital long QT syndrome has rarely been described. This case report discusses the occurrence of a clinically overt takotsubo cardiomyopathy accompanied by congenital long QT syndrome type 1 in a female patient.
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Affiliation(s)
- Ibrahim El‐Battrawy
- First Department of MedicineUniversity Medical Centre Mannheim (UMM)Faculty of Medicine MannheimUniversity of HeidelbergMannheimGermany
- DZHK (German Center for Cardiovascular Research) partner site MannheimMannheimGermany
| | - Michael Behnes
- First Department of MedicineUniversity Medical Centre Mannheim (UMM)Faculty of Medicine MannheimUniversity of HeidelbergMannheimGermany
- DZHK (German Center for Cardiovascular Research) partner site MannheimMannheimGermany
| | - Martin Borggrefe
- First Department of MedicineUniversity Medical Centre Mannheim (UMM)Faculty of Medicine MannheimUniversity of HeidelbergMannheimGermany
- DZHK (German Center for Cardiovascular Research) partner site MannheimMannheimGermany
| | - Ibrahim Akin
- First Department of MedicineUniversity Medical Centre Mannheim (UMM)Faculty of Medicine MannheimUniversity of HeidelbergMannheimGermany
- DZHK (German Center for Cardiovascular Research) partner site MannheimMannheimGermany
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10
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Zhao Y, Wang T, Guo J, Yang T, Li W, Koichopolos J, Lamothe SM, Kang Y, Ma A, Zhang S. Febrile temperature facilitates hERG/IKr degradation through an altered K(+) dependence. Heart Rhythm 2016; 13:2004-11. [PMID: 27321242 DOI: 10.1016/j.hrthm.2016.06.019] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Indexed: 12/28/2022]
Abstract
BACKGROUND Dysfunction of the rapidly activating delayed rectifier K(+) channel (IKr) encoded by the human ether-à-go-go-related gene (hERG) is the primary cause of acquired long QT syndrome (LQTS). Fever has been reported to trigger LQTS in various conditions. OBJECTIVE We aim to clarify the effect and underlying mechanisms of febrile temperature on hERG expressed in HEK cells, IKr in neonatal rat ventricular myocytes, and the QT interval in rabbits. METHODS Western blot analysis was used to determine the expression of hERG channel protein in stably transfected HEK 293 cells. Immunocytochemistry was used to visualize the localization of hERG channels. The whole-cell patch clamp technique was used to record hERG K(+) current (IhERG) in hERG expressing HEK 293 cells, as well as IKr, transient outward K(+) current (Ito), and L-type Ca(2+) current (ICa) in neonatal rat ventricular myocytes. Electrocardiographic recordings were performed in an in vivo rabbit model. RESULTS Compared with culture at 37°C, culture at 40°C reduced the mature hERG expression and IhERG in an extracellular K(+) concentration-dependent manner. Point mutations that remove the K(+) dependence of hERG-S624T and F627Y-also abolished the febrile temperature-induced hERG reduction. In neonatal rat ventricular myocytes, febrile temperature prolonged the action potential duration and selectively reduced IKr in a manner similar to low K(+) culture. In an in vivo rabbit model, fever and hypokalemia synergistically prolonged the QT interval. CONCLUSION Febrile temperature facilitates the development of LQTS by expediting hERG degradation through altered K(+) dependence.
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Affiliation(s)
- Yan Zhao
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Tingzhong Wang
- Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University School of Medicine, Xi'an, China
| | - Jun Guo
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Tonghua Yang
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Wentao Li
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Jennifer Koichopolos
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Shawn M Lamothe
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Yudi Kang
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Aiqun Ma
- Department of Cardiovascular Medicine, First Affiliated Hospital of Xi'an Jiaotong University School of Medicine, Xi'an, China
| | - Shetuan Zhang
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada,.
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Itoh H, Crotti L, Aiba T, Spazzolini C, Denjoy I, Fressart V, Hayashi K, Nakajima T, Ohno S, Makiyama T, Wu J, Hasegawa K, Mastantuono E, Dagradi F, Pedrazzini M, Yamagishi M, Berthet M, Murakami Y, Shimizu W, Guicheney P, Schwartz PJ, Horie M. The genetics underlying acquired long QT syndrome: impact for genetic screening. Eur Heart J 2015; 37:1456-64. [PMID: 26715165 DOI: 10.1093/eurheartj/ehv695] [Citation(s) in RCA: 127] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Accepted: 12/01/2015] [Indexed: 12/19/2022] Open
Abstract
AIMS Acquired long QT syndrome (aLQTS) exhibits QT prolongation and Torsades de Pointes ventricular tachycardia triggered by drugs, hypokalaemia, or bradycardia. Sometimes, QTc remains prolonged despite elimination of triggers, suggesting the presence of an underlying genetic substrate. In aLQTS subjects, we assessed the prevalence of mutations in major LQTS genes and their probability of being carriers of a disease-causing genetic variant based on clinical factors. METHODS AND RESULTS We screened for the five major LQTS genes among 188 aLQTS probands (55 ± 20 years, 140 females) from Japan, France, and Italy. Based on control QTc (without triggers), subjects were designated 'true aLQTS' (QTc within normal limits) or 'unmasked cLQTS' (all others) and compared for QTc and genetics with 2379 members of 1010 genotyped congenital long QT syndrome (cLQTS) families. Cardiac symptoms were present in 86% of aLQTS subjects. Control QTc of aLQTS was 453 ± 39 ms, shorter than in cLQTS (478 ± 46 ms, P < 0.001) and longer than in non-carriers (406 ± 26 ms, P < 0.001). In 53 (28%) aLQTS subjects, 47 disease-causing mutations were identified. Compared with cLQTS, in 'true aLQTS', KCNQ1 mutations were much less frequent than KCNH2 (20% [95% CI 7-41%] vs. 64% [95% CI 43-82%], P < 0.01). A clinical score based on control QTc, age, and symptoms allowed identification of patients more likely to carry LQTS mutations. CONCLUSION A third of aLQTS patients carry cLQTS mutations, those on KCNH2 being more common. The probability of being a carrier of cLQTS disease-causing mutations can be predicted by simple clinical parameters, thus allowing possibly cost-effective genetic testing leading to cascade screening for identification of additional at-risk family members.
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Affiliation(s)
- Hideki Itoh
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192, Japan Inserm, UMR_S1166, Paris, France Sorbonne Universités, UPMC Univ Paris 06, UMR_S1166, Institut de recherche sur les maladies cardiovasculaires, du métabolisme et de la nutrition, Paris, France Institute of Cardiometabolism and Nutrition (ICAN), Paris, France
| | - Lia Crotti
- IRCCS Istituto Auxologico Italiano, Center for Cardiac Arrhythmias of Genetic Origin and Laboratory of Cardiovascular Genetics, Milan, Italy Department of Molecular Medicine, University of Pavia, Pavia, Italy
| | - Takeshi Aiba
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center, Osaka, Japan
| | - Carla Spazzolini
- IRCCS Istituto Auxologico Italiano, Center for Cardiac Arrhythmias of Genetic Origin and Laboratory of Cardiovascular Genetics, Milan, Italy
| | - Isabelle Denjoy
- AP-HP, Hôpital Bichat, Service de Cardiologie, Centre de Référence des Maladies Cardiaques Héréditaires, Université Denis Diderot, Paris 7, Paris, France
| | - Véronique Fressart
- Inserm, UMR_S1166, Paris, France Sorbonne Universités, UPMC Univ Paris 06, UMR_S1166, Institut de recherche sur les maladies cardiovasculaires, du métabolisme et de la nutrition, Paris, France Institute of Cardiometabolism and Nutrition (ICAN), Paris, France AP-HP, Groupe Hospitalier Pitié-Salpétrière, Service de Biochimie Métabolique, UF Cardiogénétique et Myogénétique Moléculaire et Cellulaire, Paris, France
| | - Kenshi Hayashi
- Division of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Science, Kanazawa, Japan
| | - Tadashi Nakajima
- Department of Medicine and Biological Science, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Seiko Ohno
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192, Japan
| | - Takeru Makiyama
- Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Jie Wu
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192, Japan Department of Pharmacology, Medical School of Xi'an Jiaotong University, Xi'an, China
| | - Kanae Hasegawa
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192, Japan
| | - Elisa Mastantuono
- Institute of Human Genetics, Helmholtz Zentrum München, Neuherberg, Germany
| | - Federica Dagradi
- IRCCS Istituto Auxologico Italiano, Center for Cardiac Arrhythmias of Genetic Origin and Laboratory of Cardiovascular Genetics, Milan, Italy
| | - Matteo Pedrazzini
- IRCCS Istituto Auxologico Italiano, Center for Cardiac Arrhythmias of Genetic Origin and Laboratory of Cardiovascular Genetics, Milan, Italy
| | - Masakazu Yamagishi
- Division of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Science, Kanazawa, Japan
| | - Myriam Berthet
- Inserm, UMR_S1166, Paris, France Sorbonne Universités, UPMC Univ Paris 06, UMR_S1166, Institut de recherche sur les maladies cardiovasculaires, du métabolisme et de la nutrition, Paris, France Institute of Cardiometabolism and Nutrition (ICAN), Paris, France
| | - Yoshitaka Murakami
- Medical Statistics, Shiga University of Medical Science, Otsu, Shiga, Japan
| | - Wataru Shimizu
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center, Osaka, Japan Department of Cardiovascular Medicine, Nippon Medical School, Tokyo, Japan
| | - Pascale Guicheney
- Inserm, UMR_S1166, Paris, France Sorbonne Universités, UPMC Univ Paris 06, UMR_S1166, Institut de recherche sur les maladies cardiovasculaires, du métabolisme et de la nutrition, Paris, France Institute of Cardiometabolism and Nutrition (ICAN), Paris, France
| | - Peter J Schwartz
- IRCCS Istituto Auxologico Italiano, Center for Cardiac Arrhythmias of Genetic Origin and Laboratory of Cardiovascular Genetics, Milan, Italy
| | - Minoru Horie
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192, Japan
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12
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Yang KC, Nerbonne JM. Mechanisms contributing to myocardial potassium channel diversity, regulation and remodeling. Trends Cardiovasc Med 2015; 26:209-18. [PMID: 26391345 DOI: 10.1016/j.tcm.2015.07.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Revised: 07/11/2015] [Accepted: 07/12/2015] [Indexed: 01/19/2023]
Abstract
In the mammalian heart, multiple types of K(+) channels contribute to the control of cardiac electrical and mechanical functioning through the regulation of resting membrane potentials, action potential waveforms and refractoriness. There are similarly vast arrays of K(+) channel pore-forming and accessory subunits that contribute to the generation of functional myocardial K(+) channel diversity. Maladaptive remodeling of K(+) channels associated with cardiac and systemic diseases results in impaired repolarization and increased propensity for arrhythmias. Here, we review the diverse transcriptional, post-transcriptional, post-translational, and epigenetic mechanisms contributing to regulating the expression, distribution, and remodeling of cardiac K(+) channels under physiological and pathological conditions.
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Affiliation(s)
- Kai-Chien Yang
- Department of Pharmacology, National Taiwan University, Taipei, Taiwan; Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
| | - Jeanne M Nerbonne
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO; Internal Medicine, Washington University School of Medicine, St. Louis, MO; Cardiovascular Division, Washington University School of Medicine, St. Louis, MO.
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13
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Nachimuthu S, Assar MD, Schussler JM. Drug-induced QT interval prolongation: mechanisms and clinical management. Ther Adv Drug Saf 2014; 3:241-53. [PMID: 25083239 DOI: 10.1177/2042098612454283] [Citation(s) in RCA: 188] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The prolonged QT interval is both widely seen and associated with the potentially deadly rhythm, Torsades de Pointes (TdP). While it can occur spontaneously in the congenital form, there is a wide array of drugs that have been implicated in the prolongation of the QT interval. Some of these drugs have either been restricted or withdrawn from the market due to the increased incidence of fatal polymorphic ventricular tachycardia. The list of drugs that cause QT prolongation continues to grow, and an updated list of specific drugs that prolong the QT interval can be found at www.qtdrugs.org. This review focuses on the mechanism of drug-induced QT prolongation, risk factors for TdP, culprit drugs, prevention and monitoring of prolonged drug-induced QT prolongation and treatment strategies.
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Affiliation(s)
- Senthil Nachimuthu
- Baylor University Medical Center, Jack and Jane Hamilton, Heart and Vascular Hospital Dallas, TX, USA
| | - Manish D Assar
- Baylor University Medical Center, Jack and Jane Hamilton, Heart and Vascular Hospital Dallas, TX, USA
| | - Jeffrey M Schussler
- Baylor University Medical Center, Jack and Jane Hamilton, Heart and Vascular Hospital, 621 North Hall Street, Suite 500, Dallas, TX 75226, USA
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14
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Hedley PL, Durrheim GA, Hendricks F, Goosen A, Jespersgaard C, Støvring B, Pham TT, Christiansen M, Brink PA, Corfield VA. Long QT syndrome in South Africa: the results of comprehensive genetic screening. Cardiovasc J Afr 2014; 24:231-7. [PMID: 24217263 PMCID: PMC3772322 DOI: 10.5830/cvja-2013-032] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Accepted: 05/24/2013] [Indexed: 01/06/2023] Open
Abstract
Congenital long QT syndrome (cLQTS) is a genetic disorder predisposing to ventricular arrhythmia, syncope and sudden death. Over 700 different cLQTS-causing mutations in 13 genes are known. The genetic spectrum of LQTS in 44 South African cLQTS patients (23 known to carry the South African founder mutation p.A341V in KCNQ1) was established by screening for mutations in the coding regions of KCNQ1, KCNH2, KCNE1, KCNE2 and SCN5A, the most frequently implicated cLQTS-causing genes (five-gene screening). Fourteen disease-causing mutations were identified, eight (including the founder mutation) in KCNQ1, five in KCNH2 and one in KCNE1. Two mutations were novel. Two double heterozygotes were found among the 23 families (8.5%) carrying the founder mutation. In conclusion, cLQTS in South Africa reflects both a strong founder effect and a genetic spectrum similar to that seen in other populations. Consequently, five-gene screening should be offered as a standard screening option, as is the case internationally. This will disclose compound and double heterozygotes. Fivegene screening will most likely be even more informative in other South African sub-populations with a greater genetic diversity.
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Affiliation(s)
- Paula L Hedley
- US/MRC Centre for Molecular and Cellular Biology, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, University of Stellenbosch, South Africa
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15
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Schmitt N, Grunnet M, Olesen SP. Cardiac potassium channel subtypes: new roles in repolarization and arrhythmia. Physiol Rev 2014; 94:609-53. [PMID: 24692356 DOI: 10.1152/physrev.00022.2013] [Citation(s) in RCA: 160] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
About 10 distinct potassium channels in the heart are involved in shaping the action potential. Some of the K+ channels are primarily responsible for early repolarization, whereas others drive late repolarization and still others are open throughout the cardiac cycle. Three main K+ channels drive the late repolarization of the ventricle with some redundancy, and in atria this repolarization reserve is supplemented by the fairly atrial-specific KV1.5, Kir3, KCa, and K2P channels. The role of the latter two subtypes in atria is currently being clarified, and several findings indicate that they could constitute targets for new pharmacological treatment of atrial fibrillation. The interplay between the different K+ channel subtypes in both atria and ventricle is dynamic, and a significant up- and downregulation occurs in disease states such as atrial fibrillation or heart failure. The underlying posttranscriptional and posttranslational remodeling of the individual K+ channels changes their activity and significance relative to each other, and they must be viewed together to understand their role in keeping a stable heart rhythm, also under menacing conditions like attacks of reentry arrhythmia.
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16
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Abstract
Abnormal functioning of cardiac ion channels can disrupt cardiac myocyte action potentials and thus cause potentially lethal cardiac arrhythmias. Ion channel dysfunction has been observed at all stages in channel ontogeny, from biogenesis to regulation, and arises from genetic or environmental factors, or both. Acquired arrhythmias - including those that are drug induced - are more common than solely inherited arrhythmias but, in some cases, also contain an identifiable genetic component. This interplay between the pharmacology and genetics - known as 'pharmacogenetics' - of cardiac ion channels and the systems that impact them presents both challenges and opportunities to academics, pharmaceutical companies and clinicians seeking to develop and utilize therapies for cardiac rhythm disorders. In this review, we discuss ion channel pharmacogenetics in the context of both causation and treatment of cardiac arrhythmias, focusing on the long QT syndromes.
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Affiliation(s)
- Geoffrey W Abbott
- Weill Medical College of Cornell University, Greenberg Division of Cardiology, Department of Medicine and Department of Pharmacology, 520 East 70th Street, New York, NY 10021, USA.
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17
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Trolle C, Mortensen KH, Pedersen LN, Berglund A, Jensen HK, Andersen NH, Gravholt CH. Long QT interval in Turner syndrome--a high prevalence of LQTS gene mutations. PLoS One 2013; 8:e69614. [PMID: 23936059 PMCID: PMC3723856 DOI: 10.1371/journal.pone.0069614] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Accepted: 06/07/2013] [Indexed: 01/15/2023] Open
Abstract
Objectives QT-interval prolongation of unknown aetiology is common in Turner syndrome. This study set out to explore the presence of known long QT mutations in Turner syndrome and to examine the corrected QT-interval (QTc) over time and relate the findings to the Turner syndrome phenotype. Methods Adult women with Turner syndrome (n = 88) were examined thrice and 68 age-matched healthy controls were examined once. QTc was measured by one blinded reader (intra-reader variability: 0.7%), and adjusted for influence of heart rate by Bazett’s (bQTc) and Hodges’s formula (hQTc). The prevalence of mutations in genes related to Long QT syndrome was determined in women with Turner syndrome and a QTc >432.0 milliseconds (ms). Echocardiographic assessment of aortic valve morphology, 24-hour blood pressures and blood samples were done. Results The mean hQTc in women with Turner syndrome (414.0±25.5 ms) compared to controls (390.4±17.8 ms) was prolonged (p<0.001) and did not change over time (416.9±22.6 vs. 415.6±25.5 ms; p = 0.4). 45,X karyotype was associated with increased hQTc prolongation compared to other Turner syndrome karyotypes (418.2±24.8 vs. 407.6±25.5 ms; p = 0.055). In women with Turner syndrome and a bQTc >432 ms, 7 had mutations in major Long QT syndrome genes (SCN5A and KCNH2) and one in a minor Long QT syndrome gene (KCNE2). Conclusion There is a high prevalence of mutations in the major LQTS genes in women with TS and prolonged QTc. It remains to be settled, whether these findings are related to the unexplained excess mortality in Turner women. Clinical Trial Registration NCT00624949. https://register.clinicaltrials.gov/prs/app/action/SelectProtocol/sid/S0001FLI/selectaction/View/ts/3/uid/U000099E.
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Affiliation(s)
- Christian Trolle
- Department of Endocrinology and Internal Medicine and Medical Research Laboratories, Aarhus University Hospital, Aarhus, Denmark
| | - Kristian H. Mortensen
- Department of Endocrinology and Internal Medicine and Medical Research Laboratories, Aarhus University Hospital, Aarhus, Denmark
- Department of Radiology, Cambridge University Hospitals, Cambridge, United Kingdom
| | - Lisbeth N. Pedersen
- Department of Molecular Medicine, Aarhus University Hospital, Aarhus, Denmark
| | - Agnethe Berglund
- Department of Endocrinology and Internal Medicine and Medical Research Laboratories, Aarhus University Hospital, Aarhus, Denmark
| | - Henrik K. Jensen
- Department of Cardiology, Aarhus University Hospital, Aarhus, Denmark
| | - Niels H. Andersen
- Department of Cardiology, Aarhus University Hospital, Aarhus, Denmark
| | - Claus H. Gravholt
- Department of Endocrinology and Internal Medicine and Medical Research Laboratories, Aarhus University Hospital, Aarhus, Denmark
- Department of Molecular Medicine, Aarhus University Hospital, Aarhus, Denmark
- * E-mail:
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18
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Structure of the C-terminal region of an ERG channel and functional implications. Proc Natl Acad Sci U S A 2013; 110:11648-53. [PMID: 23801759 DOI: 10.1073/pnas.1306887110] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The human ether-à-go-go-related gene (hERG) encodes a K(+) channel crucial for repolarization of the cardiac action potential. EAG-related gene (ERG) channels contain a C-terminal cyclic nucleotide-binding homology domain coupled to the pore of the channel by a C-linker. Here, we report the structure of the C-linker/cyclic nucleotide-binding homology domain of a mosquito ERG channel at 2.5-Å resolution. The structure reveals that the region expected to form the cyclic nucleotide-binding pocket is negatively charged and is occupied by a short β-strand, referred to as the intrinsic ligand, explaining the lack of direct regulation of ERG channels by cyclic nucleotides. In hERG channels, the intrinsic ligand harbors hereditary mutations associated with long-QT syndrome (LQTS), a potentially lethal cardiac arrhythmia. Mutations in the intrinsic ligand affected hERG channel gating and LQTS mutations abolished hERG currents and altered trafficking of hERG channels, which explains the LQT phenotype. The structure also reveals a dramatically different conformation of the C-linker compared with the structures of the related ether-à-go-go-like K(+) and hyperpolarization-activated cyclic nucleotide-modulated channels, suggesting that the C-linker region may be highly dynamic in the KCNH, hyperpolarization-activated cyclic nucleotide-modulated, and cyclic nucleotide-gated channels.
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19
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Abstract
Digenic inheritance (DI) is the simplest form of inheritance for genetically complex diseases. By contrast with the thousands of reports that mutations in single genes cause human diseases, there are only dozens of human disease phenotypes with evidence for DI in some pedigrees. The advent of high-throughput sequencing (HTS) has made it simpler to identify monogenic disease causes and could similarly simplify proving DI because one can simultaneously find mutations in two genes in the same sample. However, through 2012, I could find only one example of human DI in which HTS was used; in that example, HTS found only the second of the two genes. To explore the gap between expectation and reality, I tried to collect all examples of human DI with a narrow definition and characterise them according to the types of evidence collected, and whether there has been replication. Two strong trends are that knowledge of candidate genes and knowledge of protein–protein interactions (PPIs) have been helpful in most published examples of human DI. By contrast, the positional method of genetic linkage analysis, has been mostly unsuccessful in identifying genes underlying human DI. Based on the empirical data, I suggest that combining HTS with growing networks of established PPIs may expedite future discoveries of human DI and strengthen the evidence for them.
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20
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Kaltenbach S, Capri Y, Rossignol S, Denjoy I, Soudée S, Aboura A, Baumann C, Verloes A. Beckwith-Wiedemann syndrome and long QT syndrome due to familial-balanced translocation t(11;17)(p15.5;q21.3) involving the KCNQ1 gene. Clin Genet 2012; 84:78-81. [PMID: 23061425 DOI: 10.1111/cge.12038] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Revised: 10/05/2012] [Accepted: 10/05/2012] [Indexed: 12/31/2022]
Abstract
We report a child with Beckwith-Wiedemann syndrome (BWS) as the consequence of an apparently balanced, maternally inherited reciprocal translocation t(11;17)(p15.5;q21.3). His mother and aunt, who inherited the translocation from their father, did not have BWS. At birth, long QT syndrome (LQTS) was diagnosed in this child and, secondarily, among apparently healthy family members carrying the translocation. By FISH analysis, the breakpoint in 11p15.5 interrupts the KCNQ1 gene between exons 2 and 10 and causes a loss of methylation of the IC2 (and thus BWS) on the maternally inherited der(11) chromosome. To explain the presence of LQTS segregating with the t(11;17) translocation in this family, we hypothesize that the translocation that interrupts KCNQ1 allow translation of an abnormal short allele that interferes in a dominant negative way with the normal isoform 1 of KCNQ1 in the heart (where this allele is not subject to parental imprint). This appears to be the first report of BWS with congenital LQTS, which should be considered as a rare but serious complication to be searched systematically in patients with BWS due to 11p15 rearrangements.
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Affiliation(s)
- S Kaltenbach
- Department of Genetics, Robert Debré University Hospital, Paris, France
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21
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Krishnan Y, Zheng R, Walsh C, Tang Y, McDonald TV. Partially dominant mutant channel defect corresponding with intermediate LQT2 phenotype. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2011; 35:3-16. [PMID: 21951015 DOI: 10.1111/j.1540-8159.2011.03222.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
BACKGROUND The hereditary Long QT Syndrome is a common cardiac disorder where ventricular repolarization is delayed, abnormally prolonging the QTc interval on electrocardiograms. LQTS is linked to various genetic loci, including the KCNH2 (HERG) gene that encodes the α-subunit of the cardiac potassium channel that carries I(Kr). Here, we report and characterize a novel pathologic missense mutation, G816V HERG, in a patient with sudden cardiac death. METHODS Autopsy-derived tissue sample was used for DNA extraction and sequencing from an unexpected sudden death victim. The G816V HERG mutation was studied using heterologous expression in mammalian cell culture, whole cell patch clamp, confocal immunofluorescence, and immunochemical analyses. RESULTS The mutant G816V HERG channel has reduced protein expression and shows a trafficking defective phenotype that is incapable of carrying current when expressed at physiological temperatures. The mutant channel showed reduced cell surface localization compared to wild-type HERG (WT HERG) but the mutant and wild-type subunits are capable of interacting. Expression studies at reduced temperatures enabled partial rescue of the trafficking defect with appearance of potassium currents, albeit with reduced current density and altered voltage-dependent activation. Lastly, we examined a potential role for hypokalemia as a contributory factor to the patient's lethal arrhythmia by possible low-potassium-induced degradation of WT HERG and haplo-insufficiency of G816V HERG. CONCLUSION The G816V mutation in HERG causes a trafficking defect that acts in a partially dominant negative manner. This intermediate severity defect agrees with the mild clinical presentation in other family members harboring the same mutation. Possible hypokalemia in the proband induced WT HERG degradation combined with haplo-insufficiency may have further compromised repolarization reserve and contributed to the lethal arrhythmia.
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Affiliation(s)
- Yamini Krishnan
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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22
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Tang Y, Siegel D, Sampson B. Molecular Investigations of Sudden Unexplained Deaths. Acad Forensic Pathol 2011. [DOI: 10.23907/2011.025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Sudden unexplained deaths in apparently healthy individuals (newborn through adult) pose a vexing challenge to medical examiners, law enforcement and society as a whole. Recent advances in “molecular autopsies” have begun to uncover the mystery surrounding sudden unexplained deaths by identifying mutations that can result in or predispose an apparently healthy individual to sudden death. Genetic risks of sudden unexplained deaths have been studied from several different perspectives, and categorized generally by systems, including: cardiac, nervous, immune, and metabolic. This article reviews the genetic risks in sudden unexplained deaths, presents the current state and challenges of molecular investigations, and sheds light on future directions in sudden unexplained death investigations.
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Affiliation(s)
- Yingying Tang
- Molecular Genetics Laboratory in the New York City Office of Chief Medical Examiner and Forensic Medicine Department at New York University School of Medicine, New York, New York
| | - Donald Siegel
- New York City Office of Chief Medical Examiner, and Forensic Medicine Department at New York University School of Medicine, New York, New York (DS, BS)
| | - Barbara Sampson
- New York City Office of Chief Medical Examiner, and Forensic Medicine Department at New York University School of Medicine, New York, New York (DS, BS)
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23
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Stump MR, Gong Q, Zhou Z. Multiple splicing defects caused by hERG splice site mutation 2592+1G>A associated with long QT syndrome. Am J Physiol Heart Circ Physiol 2010; 300:H312-8. [PMID: 21057041 DOI: 10.1152/ajpheart.00818.2010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Long QT syndrome type 2 (LQT2) is caused by mutations in the human ether-a-go-go-related gene (hERG). Cryptic splice site activation in hERG has recently been identified as a novel pathogenic mechanism of LQT2. In this report, we characterize a hERG splice site mutation, 2592+1G>A, which occurs at the 5' splice site of intron 10. Reverse transcription-PCR analyses using hERG minigenes transfected into human embryonic kidney-293 cells and HL-1 cardiomyocytes revealed that the 2592+1G>A mutation disrupted normal splicing and caused multiple splicing defects: the activation of cryptic splice sites within exon 10 and intron 10 and complete intron 10 retention. We performed functional and biochemical analyses of the major splice product, hERGΔ24, in which 24 amino acids within the cyclic nucleotide binding domain of the hERG channel COOH-terminus is deleted. Patch-clamp experiments revealed that the splice mutant did not generate hERG current. Western blot and immunostaining studies showed that mutant channels did not traffic to the cell surface. Coexpression of wild-type hERG and hERGΔ24 resulted in significant dominant-negative suppression of hERG current via the intracellular retention of the wild-type channels. Our results demonstrate that 2592+1G>A causes multiple splicing defects, consistent with the pathogenic mechanisms of long QT syndrome.
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Affiliation(s)
- Matthew R Stump
- Division of Cardiovascular Medicine, Department of Medicine, Oregon Health and Science University, Portland, Oregon 97239, USA
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24
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Harkcom WT, Abbott GW. Emerging concepts in the pharmacogenomics of arrhythmias: ion channel trafficking. Expert Rev Cardiovasc Ther 2010; 8:1161-73. [PMID: 20670193 DOI: 10.1586/erc.10.89] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Continuous, rhythmic beating of the heart requires exquisite control of expression, localization and function of cardiac ion channels - the foundations of the cardiac myocyte action potential. Disruption of any of these processes can alter the shape of the action potential, predisposing to cardiac arrhythmias. These arrhythmias can manifest in a variety of ways depending on both the channels involved and the type of disruption (i.e., gain or loss of function). As much as 1% of the population of developed countries is affected by cardiac arrhythmia each year, and a detailed understanding of the mechanism of each arrhythmia is crucial to developing and prescribing the proper therapies. Many of the antiarrhythmic drugs currently on the market were developed before the underlying cause of the arrhythmia was known, and as a result lack specificity, causing side effects. The majority of the available drugs target the conductance of cardiac ion channels, either by blocking or enhancing current through the channel. In recent years, however, it has become apparent that specific targeting of ion channel conductance may not be the most effective means for treatment. Here we review increasing evidence that suggests defects in ion channel trafficking play an important role in the etiology of arrhythmias, and small molecule approaches to correct trafficking defects will likely play an important role in the future of arrhythmia treatment.
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Affiliation(s)
- William T Harkcom
- Department of Pharmacology, Weill Medical College of Cornell University, 520 E 70th Street, New York, NY 10021, USA
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25
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Long QT syndrome with compound mutations is associated with a more severe phenotype: a Japanese multicenter study. Heart Rhythm 2010; 7:1411-8. [PMID: 20541041 DOI: 10.1016/j.hrthm.2010.06.013] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2010] [Accepted: 06/03/2010] [Indexed: 11/24/2022]
Abstract
BACKGROUND Long QT syndrome (LQTS) can be caused by mutations in the cardiac ion channels. Compound mutations occur at a frequency of 4% to 11% among genotyped LQTS cases. OBJECTIVE The purpose of this study was to determine the clinical characteristics and manner of onset of cardiac events in Japanese patients with LQTS and compound mutations. METHODS Six hundred three genotyped LQTS patients (310 probands and 293 family members) were divided into two groups: those with a single mutation (n = 568) and those with two mutations (n = 35). Clinical phenotypes were compared between the two groups. RESULTS Of 310 genotyped probands, 26 (8.4%) had two mutations in the same or different LQTS-related genes (compound mutations). Among the 603 LQTS patients, compound mutation carriers had significantly longer QTc interval (510 ± 56 ms vs 478± 53 ms, P = .001) and younger age at onset of cardiac events (10 ± 8 years vs 18 ± 16 years, P = .043) than did single mutation carriers. The incidence rate of cardiac events before age 40 years and use of beta-blocker therapy among compound mutation carriers also were different than in single mutation carriers. Subgroup analysis showed more cardiac events in LQTS type 1 (LQT1) and type 2 (LQT2) compound mutations compared to single LQT1 and LQT2 mutations. CONCLUSION Compound mutation carriers are associated with a more severe phenotype than single mutation carriers.
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26
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Hayashi K, Shuai W, Sakamoto Y, Higashida H, Yamagishi M, Kupershmidt S. Trafficking-competent KCNQ1 variably influences the function of HERG long QT alleles. Heart Rhythm 2010; 7:973-80. [PMID: 20348026 DOI: 10.1016/j.hrthm.2010.03.038] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Accepted: 03/25/2010] [Indexed: 01/08/2023]
Abstract
BACKGROUND Mutations in the KCNQ1 and human ether-a-go-go-related gene (HERG) genes cause the long QT syndromes, LQTS1 and LQTS2, due to reductions in the cardiac repolarizing I(Ks) and I(Kr) currents, respectively. It was previously reported that KCNQ1 coexpression modulates HERG function by enhancing membrane expression of HERG, and that the 2 proteins coimmunoprecipitate, and colocalize in myocytes. In vivo studies in genetically modified rabbits also support a HERG-KCNQ1 interaction. OBJECTIVE We sought to determine whether KCNQ1 influences the current characteristics of HERG genetic variants. METHODS This study used expression of HERG and KCNQ1 wild-type (WT) and mutant channels in heterologous systems, combined with whole-cell patch clamp analysis and biochemistry. RESULTS Supporting the notion that KCNQ1 needs to be trafficking competent to influence HERG function, we found that although the tail current density of HERG expressed in Chinese Hamster Ovary (CHO) cells was approximately doubled by WT KCNQ1 coexpression, it was not altered in the presence of the trafficking-defective KCNQ1(T587M) variant. Activation and deactivation kinetics of HERG variants were not altered. The HERG(M124T) variant, previously shown to be mildly impaired functionally, was restored to WT levels by KCNQ1-WT but not KCNQ1(T587M) coexpression. The tail current densities of the severely trafficking-impaired HERG(G601S) and HERG(F805C) variants were only slightly improved by KCNQ1 coexpression. The trafficking competent but incompletely processed HERG(N598Q), and a mutation in the selectivity filter, HERG(G628S), were not improved by KCNQ1 coexpression. CONCLUSION These findings suggest a functional codependence of HERG on KCNQ1 during channel biogenesis. Moreover, KCNQ1 variably modulates LQTS2 mutations with distinct underlying pathologies.
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Affiliation(s)
- Kenshi Hayashi
- Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6602, USA
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Hedley PL, Jørgensen P, Schlamowitz S, Wangari R, Moolman-Smook J, Brink PA, Kanters JK, Corfield VA, Christiansen M. The genetic basis of long QT and short QT syndromes: A mutation update. Hum Mutat 2009; 30:1486-511. [DOI: 10.1002/humu.21106] [Citation(s) in RCA: 318] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Guo J, Massaeli H, Xu J, Jia Z, Wigle JT, Mesaeli N, Zhang S. Extracellular K+ concentration controls cell surface density of IKr in rabbit hearts and of the HERG channel in human cell lines. J Clin Invest 2009; 119:2745-57. [PMID: 19726881 DOI: 10.1172/jci39027] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2009] [Accepted: 06/10/2009] [Indexed: 12/19/2022] Open
Abstract
Although the modulation of ion channel gating by hormones and drugs has been extensively studied, much less is known about how cell surface ion channel expression levels are regulated. Here, we demonstrate that the cell surface density of both the heterologously expressed K+ channel encoded by the human ether-a-go-go-related gene (HERG) and its native counterpart, the rapidly activating delayed rectifier K+ channel (IKr), in rabbit hearts in vivo is precisely controlled by extracellular K+ concentration ([K+]o) within a physiologically relevant range. Reduction of [K+]o led to accelerated internalization and degradation of HERG channels within hours. Confocal analysis revealed colocalization between HERG and ubiquitin during the process of HERG internalization, and overexpression of ubiquitin facilitated HERG degradation under low [K+]o. The HERG channels colocalized with a marker of multivesicular bodies during internalization, and the internalized HERG channels were targeted to lysosomes. Our results provide the first evidence to our knowledge that the cell surface density of a voltage-gated K+ channel, HERG, is regulated by a biological factor, extracellular K+. Because hypokalemia is known to exacerbate long QT syndrome (LQTS) and Torsades de pointes tachyarrhythmias, our findings provide a potential mechanistic link between hypokalemia and LQTS.
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Affiliation(s)
- Jun Guo
- Department of Physiology, Queen's University, Kingston, Ontario, Canada
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Biliczki P, Girmatsion Z, Brandes RP, Harenkamp S, Pitard B, Charpentier F, Hébert TE, Hohnloser SH, Baró I, Nattel S, Ehrlich JR. Trafficking-deficient long QT syndrome mutation KCNQ1-T587M confers severe clinical phenotype by impairment of KCNH2 membrane localization: evidence for clinically significant IKr-IKs alpha-subunit interaction. Heart Rhythm 2009; 6:1792-801. [PMID: 19959132 DOI: 10.1016/j.hrthm.2009.08.009] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/26/2009] [Accepted: 08/06/2009] [Indexed: 12/27/2022]
Abstract
BACKGROUND KCNQ1-T587M is a trafficking-deficient long QT syndrome (LQTS) missense mutation. Affected patients exhibit severe clinical phenotypes that are not explained by the mutant's effects on I(Ks). Previous work showed a KCNH2 and KCNQ1 alpha-subunit interaction that increases KCNH2 membrane localization and function. OBJECTIVE We hypothesized that failure of trafficking-deficient KCNQ1-T587M to enhance KCNH2 membrane expression could reduce KCNH2 current versus wild-type KCNQ1 (KCNQ1-WT), contributing to the LQTS phenotype of KCNQ1-T587M carriers. METHODS Patch-clamp, protein biochemical studies, confocal imaging, and in vivo transfection of guinea pig cardiomyocytes were performed. RESULTS KCNQ1-T587M failed to generate functional current when coexpressed with KCNE1 and caused haploinsufficiency when coexpressed with KCNQ1-WT/KCNE1. Coexpression of KCNQ1-WT with KCNH2 increased I(KCNH2) versus KCNH2 alone (P <.05). Immunoblots and confocal microscopy indicated increased plasma membrane localization of KCNH2 alpha-subunits in cells cotransfected with KCNQ1-WT plasmid, while total KCNH2 protein synthesis and KCNH2 glycosylation remained unaffected, which suggests a chaperone effect of KCNQ1-WT to enhance the membrane localization of KCNH2. KCNH2 also coimmunoprecipitated with KCNQ1-WT. Although KCNQ1-T587M coprecipitated with KCNH2, the mutant was retained intracellularly and failed to increase KCNH2 membrane localization, abolishing the KCNQ1-WT chaperone function and reducing I(KCNH2) upon coexpression substantially compared with coexpression with KCNQ1-WT (P <.05). In vivo transfection of KCNQ1-T587M in guinea pigs suppressed I(Kr) in isolated cardiomyocytes. CONCLUSION The trafficking-deficient LQTS mutation KCNQ1-T587M fails to show the chaperoning function that enhances KCNH2 membrane localization with KCNQ1-WT. This novel mechanism results in reduced I(KCNH2), which would be expected to decrease repolarization reserve and synergize with reduced I(KCNQ1) caused directly by the mutation, potentially explaining the malignant clinical phenotype in affected patients.
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Affiliation(s)
- Peter Biliczki
- Div. of Cardiology, Section of Electrophysiology, Goethe-Universität, Frankfurt, Germany
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Brelidze TI, Carlson AE, Zagotta WN. Absence of direct cyclic nucleotide modulation of mEAG1 and hERG1 channels revealed with fluorescence and electrophysiological methods. J Biol Chem 2009; 284:27989-27997. [PMID: 19671703 DOI: 10.1074/jbc.m109.016337] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Similar to CNG and HCN channels, EAG and ERG channels contain a cyclic nucleotide binding domain (CNBD) in their C terminus. While cyclic nucleotides have been shown to facilitate opening of CNG and HCN channels, their effect on EAG and ERG channels is less clear. Here we explored cyclic nucleotide binding and modulation of mEAG1 and hERG1 channels with fluorescence and electrophysiology. Binding of cyclic nucleotides to the isolated CNBD of mEAG1 and hERG1 channels was examined with two independent fluorescence-based methods: changes in tryptophan fluorescence and fluorescence of an analog of cAMP, 8-NBD-cAMP. As a positive control for cyclic nucleotide binding we used changes in the fluorescence of the isolated CNBD of mHCN2 channels. Our results indicated that cyclic nucleotides do not bind to the isolated CNBD domain of mEAG1 channels and bind with low affinity (K(d) > or = 51 microm) to the isolated CNBD of hERG1 channels. Consistent with the results on the isolated CNBD, application of cyclic nucleotides to inside-out patches did not affect currents recorded from mEAG1 channels. Surprisingly, despite its low affinity binding to the isolated CNBD, cAMP also had no effect on currents from hERG1 channels even at high concentrations. Our results indicate that cyclic nucleotides do not directly modulate mEAG1 and hERG1 channels. Further studies are necessary to determine if the CNBD in the EAG family of K(+) channels might harbor a binding site for a ligand yet to be uncovered.
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Affiliation(s)
- Tinatin I Brelidze
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195; Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195
| | - Anne E Carlson
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195
| | - William N Zagotta
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195; Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195.
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Sankaranarayanan K, Varshney A, Mathew MK. N type rapid inactivation in human Kv1.4 channels: functional role of a putative C-terminal helix. Mol Membr Biol 2009; 22:389-400. [PMID: 16308273 DOI: 10.1080/09687860500190663] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Voltage gated potassium channels are tetrameric membrane proteins, which have a central role in cellular excitability. Human Kv1.4 channels open on membrane depolarization and inactivate rapidly by a 'ball and chain' mechanism whose molecular determinants have been mapped to the cytoplasmic N terminus of the channel. Here we show that the other terminal end of the channel also plays a role in channel inactivation. Swapping the C-terminal residues of hKv1.4 with those from two non-inactivating channels (hKv1.1 and hKv1.2) affects the rates of inactivation, as well as the recovery of the channel from the inactivated state. Secondary structure predictions of the hKv1.4 sequence reveal a helical structure at its distal C-terminal. Complete removal or partial disruption of this helical region results in channels with remarkably slowed inactivation kinetics. The ionic selectivity and voltage-dependence of channel opening were similar to hKv1.4, indicative of an unperturbed channel pore. These results demonstrate that fast inactivation is modulated by structural elements in the C-terminus, suggesting that the process involves the concerted action of the N- and C-termini.
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Schulze-Bahr E. Susceptibility genes & modifiers for cardiac arrhythmias. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 98:289-300. [DOI: 10.1016/j.pbiomolbio.2009.01.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Cellular properties of C-terminal KCNH2 long QT syndrome mutations: Description and divergence from clinical phenotypes. Heart Rhythm 2008; 5:1159-67. [DOI: 10.1016/j.hrthm.2008.04.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/05/2008] [Accepted: 04/15/2008] [Indexed: 11/22/2022]
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Killeen MJ, Thomas G, Olesen SP, Demnitz J, Stokoe KS, Grace AA, Huang CLH. Effects of potassium channel openers in the isolated perfused hypokalaemic murine heart. Acta Physiol (Oxf) 2008; 193:25-36. [PMID: 18005217 PMCID: PMC2343060 DOI: 10.1111/j.1748-1716.2007.01773.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Aim We explored the anti-arrhythmic efficacy of K+ channel activation in the hypokalaemic murine heart using NS1643 and nicorandil, compounds which augment IKr and IKATP respectively. Methods Left ventricular epicardial and endocardial monophasic action potentials were compared in normokalaemic and hypokalaemic preparations in the absence and presence of NS1643 (30 μm) and nicorandil (20 μm). Results Spontaneously beating hypokalaemic hearts (3 mm K+) all elicited early afterdepolarizations (EADs) and episodes of ventricular tachycardia (VT). Perfusion with NS1643 and nicorandil suppressed EADs and VT in 7 of 13 and five of six hypokalaemic hearts. Provoked arrhythmia studies using programmed electrical stimulation induced VT in all hypokalaemic hearts, but failed to do so in 7 of 13 and five of six hearts perfused with NS1643 and nicorandil respectively. These anti-arrhythmic effects were accompanied by reductions in action potential duration at 90% repolarization (APD90) and changes in the transmural gradient of repolarization, reflected in ΔAPD90. NS1643 and nicorandil reduced epicardial APD90 from 68.3 ± 1.1 to 56.5 ± 4.1 and 51.5 ± 1.5 ms, respectively, but preserved endocardial APD90 in hypokalaemic hearts. NS1643 and nicorandil thus restored ΔAPD90 from −9.6 ± 4.3 ms under baseline hypokalaemic conditions to 3.9 ± 4.1 and 9.9 ± 2.1 ms, respectively, close to normokalaemic values. Conclusion These findings demonstrate, for the first time, the anti-arrhythmic efficacy of K+ channel activation in the setting of hypokalaemia. NS1643 and nicorandil are anti-arrhythmic through the suppression of EADs, reductions in APD90 and restorations of ΔAPD90.
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Affiliation(s)
- M J Killeen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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Killeen MJ, Gurung IS, Thomas G, Stokoe KS, Grace AA, Huang CLH. Separation of early afterdepolarizations from arrhythmogenic substrate in the isolated perfused hypokalaemic murine heart through modifiers of calcium homeostasis. Acta Physiol (Oxf) 2007; 191:43-58. [PMID: 17524066 PMCID: PMC2040229 DOI: 10.1111/j.1748-1716.2007.01715.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
AIMS We resolved roles for early afterdepolarizations (EADs) and transmural gradients of repolarization in arrhythmogenesis in Langendorff-perfused hypokalaemic murine hearts paced from the right ventricular epicardium. METHODS Left ventricular epicardial and endocardial monophasic action potentials (MAPs) and arrhythmogenic tendency were compared in the presence and absence of the L-type Ca(2+) channel blocker nifedipine (10 nm-1 microm) and the calmodulin kinase type II inhibitor KN-93 (2 microm). RESULTS All the hypokalaemic hearts studied showed prolonged epicardial and endocardial MAPs, decreased epicardial-endocardial APD(90) difference, EADs, triggered beats and ventricular tachycardia (VT) (n = 6). In all spontaneously beating hearts, 100 (but not 10) nm nifedipine reduced both the incidence of EADs and triggered beats from 66.9 +/- 15.7% to 28.3 +/- 8.7% and episodes of VT from 10.8 +/- 6.3% to 1.2 +/- 0.7% of MAPs (n = 6 hearts, P < 0.05); 1 microm nifedipine abolished all these phenomena (n = 6). In contrast programmed electrical stimulation (PES) still triggered VT in six of six hearts with 0, 10 and 100 nm but not 1 microm nifedipine. 1 microm nifedipine selectively reduced epicardial (from 66.1 +/- 3.4 to 46.2 +/- 2.5 ms) but not endocardial APD(90), thereby restoring DeltaAPD(90) from -5.9 +/- 2.5 to 15.5 +/- 3.2 ms, close to normokalaemic values. KN-93 similarly reduced EADs, triggered beats and VT in spontaneously beating hearts to 29.6 +/- 8.9% and 1.7 +/- 1.1% respectively (n = 6) yet permitted PES-induced VT (n = 6), in the presence of a persistently negative DeltaAPD(90). CONCLUSIONS These findings empirically implicate both EADs and triggered beats alongside arrhythmogenic substrate of DeltaAPD(90) in VT pathogenesis at the whole heart level.
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Affiliation(s)
- M J Killeen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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Chevalier P, Bellocq C, Millat G, Piqueras E, Potet F, Schott JJ, Baró I, Lemarec H, Barhanin J, Rousson R, Rodriguez-Lafrasse C. Torsades de pointes complicating atrioventricular block: Evidence for a genetic predisposition. Heart Rhythm 2007; 4:170-4. [PMID: 17275752 DOI: 10.1016/j.hrthm.2006.10.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/06/2006] [Accepted: 10/03/2006] [Indexed: 11/26/2022]
Abstract
BACKGROUND The prevalence of genetic risk factors has not been systematically evaluated in the setting of complete atriventricular (AV) block complicated by long QT syndrome (LQTS). OBJECTIVE This study was performed to determine to what extent acquired LQTS in the context of AV block has a genetic substrate. METHODS Among 420 recipients of pacemakers implanted over a 3-year period, we identified retrospectively 29 patients with complete AV block and a QT interval >600 ms in duration. A second study group included 22 randomly selected patients who had AV block and a QT interval <600 ms. Normal controls were 100 consecutive individuals without medical history. Genetic studies screening for HERG, KCNQ1 KCNE1, KCNE2, and SCN5A mutations were performed. RESULTS We identified four mutations on genes encoding potassium channels in five patients with AV block and acquired LQTS. These mutations were not found among patients with AV block and a QT interval <600 ms in duration or in healthy volunteers. Functional expression of three HERG mutations (R328C, R696C, and R1047L) had a dominant negative effect on wild-type I(Kr). One KCNE2 mutation (R77W) identified in a patient treated with flecainide did not alter I(Kr). CONCLUSIONS This study showed that complete AV block complicated by LQTS was associated with HERG mutations in 17% of cases. Further studies are needed to identify factors, genetic or environmental, which may be implicated in bradycardia-related abnormalities of ventricular repolarization.
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Killeen MJ, Thomas G, Gurung IS, Goddard CA, Fraser JA, Mahaut-Smith MP, Colledge WH, Grace AA, Huang CLH. Arrhythmogenic mechanisms in the isolated perfused hypokalaemic murine heart. Acta Physiol (Oxf) 2007; 189:33-46. [PMID: 17280555 PMCID: PMC1859975 DOI: 10.1111/j.1748-1716.2006.01643.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Aim Hypokalaemia is associated with a lethal form of ventricular tachycardia (VT), torsade de pointes, through pathophysiological mechanisms requiring clarification. Methods Left ventricular endocardial and epicardial monophasic action potentials were compared in isolated mouse hearts paced from the right ventricular epicardium perfused with hypokalaemic (3 and 4 mm [K+]o) solutions. Corresponding K+ currents were compared in whole-cell patch-clamped epicardial and endocardial myocytes. Results Hypokalaemia prolonged epicardial action potential durations (APD) from mean APD90s of 37.2 ± 1.7 ms (n = 7) to 58.4 ± 4.1 ms (n =7) and 66.7 ± 2.1 ms (n = 11) at 5.2, 4 and 3 mm [K+]o respectively. Endocardial APD90s correspondingly increased from 51.6 ± 1.9 ms (n = 7) to 62.8 ± 2.8 ms (n = 7) and 62.9 ± 5.9 ms (n = 11) giving reductions in endocardial–epicardial differences, ΔAPD90, from 14.4 ± 2.6 to 4.4 ± 5.0 and −3.4 ± 6.0 ms respectively. Early afterdepolarizations (EADs) occurred in epicardia in three of seven spontaneously beating hearts at 4 mm [K+]o with triggered beats followed by episodes of non-sustained VT in nine of 11 preparations at 3 mm. Programmed electrical stimulation never induced arrhythmic events in preparations perfused with normokalemic solutions yet induced VT in two of seven and nine of 11 preparations at 4 and 3 mm [K+]o respectively. Early outward K+ current correspondingly fell from 73.46 ± 8.45 to 61.16±6.14 pA/pF in isolated epicardial but not endocardial myocytes (n = 9) (3 mm [K+]o). Conclusions Hypokalaemic mouse hearts recapitulate the clinical arrhythmogenic phenotype, demonstrating EADs and triggered beats that might initiate VT on the one hand and reduced transmural dispersion of repolarization reflected in ΔAPD90 suggesting arrhythmogenic substrate on the other.
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Affiliation(s)
- M J Killeen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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Ching CK, Tan EC. Congenital long QT syndromes: clinical features, molecular genetics and genetic testing. Expert Rev Mol Diagn 2006; 6:365-74. [PMID: 16706739 DOI: 10.1586/14737159.6.3.365] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Congenital long QT syndrome (LQTS) is a primary electrical disease characterized by a prolonged QT interval in the surface electrocardiogram and increased predisposition to a typical polymorphic ventricular tachycardia, termed Torsade de Pointes. Most patients with LQTS are asymptomatic and are diagnosed incidentally based on an electrocardiogram. Symptomatic patients may suffer from severe cardiac events, such as syncope and/or sudden cardiac death. Autosomal dominant forms are caused by heterozygous mutations in genes encoding the components of the ion channels. The autosomal recessive form with congenital deafness is also known as Jervell and Lang-Nielsen syndrome. It is caused by homozygous mutations or certain compound heterozygous mutations. Depending on the genetic defects, there are differences in the age of onset, severity of symptoms, and number of cardiac events and event triggers. With advances in gene technology, it is now feasible to perform genetic testing for LQTS, especially for those with family history. Identification of the mutation will lead to better management of symptoms and more targeted treatment, depending on the underlying genetic defect, resulting in a reduction of mortality and cardiac events.
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Affiliation(s)
- Chi-Keong Ching
- National Heart Centre, Department of Cardiology, National Heart Centre, Mistri Wing 17 Third Hospital Avenue, Singapore 168752, Republic of Singapore
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Roepke TK, Abbott GW. Pharmacogenetics and cardiac ion channels. Vascul Pharmacol 2006; 44:90-106. [PMID: 16344000 DOI: 10.1016/j.vph.2005.07.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Accepted: 07/01/2005] [Indexed: 12/19/2022]
Abstract
Ion channels control electrical excitability in living cells. In mammalian heart, the opposing actions of Na(+) and Ca(2+) ion influx, and K(+) ion efflux, through cardiac ion channels determine the morphology and duration of action potentials in cardiac myocytes, thus controlling the heartbeat. The last decade has seen a leap in our understanding of the molecular genetic origins of inherited cardiac arrhythmia, largely through identification of mutations in cardiac ion channels and the proteins that regulate them. Further, recent advances have shown that 'acquired arrhythmias', which occur more commonly than inherited arrhythmias, arise due to a variety of environmental factors including side effects of therapeutic drugs and often have a significant genetic component. Here, we review the pharmacogenetics of cardiac ion channels-the interplay between genetic and pharmacological factors that underlie human cardiac arrhythmias.
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Affiliation(s)
- Torsten K Roepke
- Greenberg Division of Cardiology, Department of Medicine, Cornell University, Weill Medical College, 520 East 70th Street, New York, NY 10021, USA
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Fodstad H, Bendahhou S, Rougier JS, Laitinen-Forsblom PJ, Barhanin J, Abriel H, Schild L, Kontula K, Swan H. Molecular characterization of two founder mutations causing long QT syndrome and identification of compound heterozygous patients. Ann Med 2006; 38:294-304. [PMID: 16754261 DOI: 10.1080/07853890600756065] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Mutations of at least six different genes have been found to cause long QT syndrome (LQTS), an inherited arrhythmic disorder characterized by a prolonged QT interval on the electrocardiogram (ECG), ventricular arrhythmias and risk of sudden death. AIM The aims were to define the yet undetermined phenotypic characteristics of two founder mutations and to study clinical features in compound heterozygotes identified during the course of the study. METHODS To maximize identification of the compound heterozygotes, we used an extended group of LQTS patients comprising 700 documented or suspected cases. Functional studies were carried out upon transient expression in COS-7 or HEK293 cells. RESULTS The KCNQ1 IVS7-2A>G (KCNQ1-FinB) mutation associated with a mean QTc interval of 464 ms and a complete loss-of-channel function. The HERG R176W (HERG-FinB) mutation caused a reduction in current density as well as slight acceleration of the deactivation kinetics in vitro, and its carriers had a mean QTc of 448 ms. The HERG R176W mutation was also present in 3 (0.9%) out of 317 blood donors. A total of six compound heterozygotes were identified who had the HERG R176W mutation in combination with a previously reported LQTS mutation (KCNQ1 G589D or IVS7-2A>G). When present simultaneously with an apparent LQTS-causing mutation, the HERG R176W mutation may exert an additional in vivo phenotypic effect. CONCLUSIONS The HERG R176W mutation represents a population-prevalent mutation predisposing to LQTS. Compound heterozygosity for mutant LQTS genes may modify the clinical picture in LQTS.
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Affiliation(s)
- Heidi Fodstad
- Biomedicum Helsinki and Department of Medicine, University of Helsinki, Finland, and Service of Cardiology, University Hospital, Lausanne, Switzerland.
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Shang YP, Xie XD, Wang XX, Chen JZ, Zhu JH, Tao QM, Zheng LR. A novel splice mutation of HERG in a Chinese family with long QT syndrome. J Zhejiang Univ Sci B 2005; 6:626-30. [PMID: 15973763 PMCID: PMC1389795 DOI: 10.1631/jzus.2005.b0626] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Congenital long QT syndrome (LQTS) is a genetically heterogeneous disease in which six ion-channel genes have been identified. The phenotype-genotype relationships of the HERG (human ether-a-go-go-related gene) mutations are not fully understood. The objective of this study is to identify the underlying genetic basis of a Chinese family with LQTS and to characterize the clinical manifestations properties of the mutation. Single strand conformation polymorphism (SSCP) analyses were conducted on DNA fragments amplified by polymerase chain reaction from five LQT-related genes. Aberrant conformers were analyzed by DNA sequencing. A novel splice mutation in C-terminus of HERG was identified in this Chinese LQTS family, leading to the deletion of 11-bp at the acceptor splice site of Exon9 [Exon9 IVS del (-12-->-2)]. The mutation might affect, through deficient splicing, the putative cyclic nucleotide binding domain (CNBD) of the HERG K(+) channel. This mutation resulted in a mildly affected phenotype. Only the proband had a history of syncopes, while the other three individuals with long QT interval had no symptoms. Two other mutation carriers displayed normal phenotype. No sudden death occurred in the family. The 4 affected individuals and the two silent mutation carriers were all heterozygous for the mutation. It is the first splice mutation of HERG reported in Chinese LQTS families. Clinical data suggest that the CNBD mutation may be less malignant than mutations occurring in the pore region and be partially dominant over wild-type function.
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Grunnet M, Behr ER, Calloe K, Hofman-Bang J, Till J, Christiansen M, McKenna WJ, Olesen SP, Schmitt N. Functional assessment of compound mutations in the KCNQ1 and KCNH2 genes associated with long QT syndrome. Heart Rhythm 2005; 2:1238-49. [PMID: 16253915 DOI: 10.1016/j.hrthm.2005.07.025] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/20/2005] [Accepted: 07/25/2005] [Indexed: 10/25/2022]
Abstract
BACKGROUND Long QT syndrome (LQTS) is a cardiovascular disorder characterized by prolonged QTc time, syncope, or sudden death caused by torsades de pointes and ventricular fibrillation. We investigated the clinical and electrophysiologic phenotype of individual mutations and the compound mutations in a family in which different genotypes could be found. OBJECTIVES The purpose of this study was to determine the impact of genotype-based diagnostic assessment in LQTS. METHODS We used cascade screening and functional analyses to investigate the phenotype in a family with LQTS. The contributions of the compound mutations in the KCNQ1 and KCNH2 genes (KCNQ1 R591H, KCNH2 R328C) were analyzed by heterologous expression in Xenopus laevis oocytes using two-electrode voltage clamp and by confocal imaging. RESULTS KCNH2 R328C did not show any functional phenotype whereas KCNQ1 R591H resulted in severe reduction of current. Neither wild-type nor mutant channels affected each other functionally in coexpression experiments. Therefore, a direct interaction between KCNQ1 and KCNH2 was ruled out under these conditions. CONCLUSION Assessment of novel mutational findings in LQTS should include accurate genetic and functional analysis. Notably, appropriate studies are needed if two or more mutations in different genes are present in one proband. Our findings prompt reconsideration of the impact of compound mutations in LQTS families and reinforce the need for thorough functional evaluation of novel ion channel mutations before assignment of pathogenic status.
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Affiliation(s)
- Morten Grunnet
- Department of Medical Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen N, Denmark.
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Simpson BR, Albanese RP. Ziprasidone and hypokalemia: a case of 2 predisposing factors for QTc prolongation without development of torsades de pointes. PRIMARY CARE COMPANION TO THE JOURNAL OF CLINICAL PSYCHIATRY 2005; 7:134-6. [PMID: 16027770 PMCID: PMC1163276 DOI: 10.4088/pcc.v07n0312] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Yamaguchi M, Shimizu M, Ino H, Terai H, Hayashi K, Kaneda T, Mabuchi H, Sumita R, Oshima T, Hoshi N, Higashida H. Compound heterozygosity for mutations Asp611→Tyr in KCNQ1 and Asp609→Gly in KCNH2 associated with severe long QT syndrome. Clin Sci (Lond) 2005; 108:143-50. [PMID: 15500450 DOI: 10.1042/cs20040220] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
LQTS (long QT syndrome) is an inherited cardiac disorder characterized by prolongation of QT interval, torsades de pointes and sudden death. We have identified two heterozygous missense mutations in the KCNQ1 and KCNH2 (also known as HERG) genes [Asp611→Tyr (D611Y) in KCNQ1 and Asp609→Gly (D609G) in KCNH2] in a 2-year-old boy with LQTS. The aim of the present study was to characterize the contributions of the mutations in the KCNQ1 and KCNH2 genes relative to the clinical manifestations and electrophysiological properties of LQTS. Six of 11 carriers of D611Y in KCNQ1 had long QT intervals. D609G in KCNH2 was detected only in the proband. Studies on the electrophysiological alterations due to the two missense mutations revealed that the D611Y mutation in KCNQ1 did not show a significant suppression of the currents compared with wild-type, but the time constants of current activation in the mutants were increased compared with that in the wild-type. In contrast, the D609G mutation in KCNH2 showed a dominant-negative suppression. Our results suggest that the mild phenotype produced by the D611Y mutation in KCNQ1 became more serious by addition of the D609G mutation in KCNH2 in the proband.
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Affiliation(s)
- Masato Yamaguchi
- Molecular Genetics of Cardiovascular Disorders, Division of Cardiovascular Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8640, Japan
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Sasano T, Ueda K, Orikabe M, Hirano Y, Kawano S, Yasunami M, Isobe M, Kimura A, Hiraoka M. Novel C-terminus frameshift mutation, 1122fs/147, of HERG in LQT2: additional amino acids generated by frameshift cause accelerated inactivation. J Mol Cell Cardiol 2004; 37:1205-11. [PMID: 15572050 DOI: 10.1016/j.yjmcc.2004.09.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/04/2004] [Revised: 08/17/2004] [Accepted: 09/17/2004] [Indexed: 11/16/2022]
Abstract
OBJECTIVE The function of the C-terminus region of the human ether-a-go-go related gene (HERG) has not been well characterized except for its involvement in trafficking. To understand further the role of C-terminus region, we performed a functional analysis of a novel frameshift mutation (1122fs/147) identified in a Japanese long QT syndrome 2 (LQT2) patient who had recurrent episodes of syncope. METHODS Wild type (WT) and mutant HERG plasmids were transfected into human embryonic kidney (HEK-293) cells, and whole-cell current was recorded by the patch-clamp technique. Confocal microscopy was performed to examine the membrane distribution of channel protein using a green fluorescent protein tagged to the N-terminus of HERG. RESULTS The mutant 1122fs/147 alone could express current, but reduced density by 74% of control. No dominant negative effect was noted with co-expression of WT and 1122fs/147. Activation and deactivation time constants were not changed, while inactivation was accelerated in 1122fs/147 compared to WT, and V(1/2) of steady-state inactivation curve shifted by 11 mV in the negative direction. Current density of 1123stop mutant revealed 49% reduction compared to WT and showed no shift in steady-state inactivation. Confocal microscopy revealed reduced protein expression on the cell surface both in 1122fs/147 and 1123stop mutants compared to WT. CONCLUSION Frameshift mutation at the C-terminus region with additional 147 amino acids evoked a loss of function of the HERG channel. A negative shift in steady-state inactivation induced by the additional 147 amino acids and trafficking defect contribute to a reduced current amplitude of 1122fs/147.
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Affiliation(s)
- Tetsuo Sasano
- Department of Cardiovascular Disease, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8510, Japan.
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Zhang L, Vincent GM, Baralle M, Baralle FE, Anson BD, Benson DW, Whiting B, Timothy KW, Carlquist J, January CT, Keating MT, Splawski I. An intronic mutation causes long QT syndrome. J Am Coll Cardiol 2004; 44:1283-91. [PMID: 15364333 DOI: 10.1016/j.jacc.2004.06.045] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/12/2004] [Revised: 06/03/2004] [Accepted: 06/07/2004] [Indexed: 11/22/2022]
Abstract
OBJECTIVES The purpose of this research was to determine whether an intronic variant (T1945+6C) in KCNH2 is a disease-causing mutation, and if expanded phenotyping criteria produce improved identification of long QT syndrome (LQTS) patients. BACKGROUND Long QT syndrome is usually caused by mutations in conserved coding regions or invariant splice sites, yet no mutation is found in 30% to 50% of families. In one such family, we identified an intronic variant in KCNH2. Long QT syndrome diagnosis is hindered by reduced penetrance, as the long QT phenotype is absent on baseline electrocardiogram (ECG) in about 30%. METHODS Fifty-two family members were phenotyped by baseline QTc, QTc maximum on serial ECGs (Ser QTc-max), and on exercise ECGs (Ex QTc-max) and by T-wave patterns. Linkage analysis tested association of the intronic change with phenotype. The consequences of T1945+6C on splicing was studied using a minigene system and on function by heterologous expression. RESULTS Expanded phenotype/pedigree criteria identified 23 affected and 29 unaffected. Affected versus unaffected had baseline QTc 484 +/- 48 ms versus 422 +/- 20 ms, Ser QTc-max 508 +/- 48 ms versus 448 +/- 10 ms, Ex QTc-max 513 +/- 54 ms versus 444 +/- 11 ms, and LQT2 T waves in 87% versus 0%. Linkage analysis demonstrated a logarithm of odds score of 10.22. Splicing assay showed T1945+6C caused downstream intron retention. Complementary deoxyribonucleic acid with retained intron 7 failed to produce functional channels. CONCLUSIONS T1945+6C is a disease-causing mutation. It alters KCNH2 splicing and cosegregates with the LQT2 phenotype. Expanded ECG criteria plus pedigree analysis provided accurate clinical diagnosis of all carriers including those with reduced penetrance. Intronic mutations may be responsible for LQTS in some families with otherwise negative mutation screening.
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Affiliation(s)
- Li Zhang
- LDS Hospital, Salt Lake City, Utah 84103, USA
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Schwartz PJ, Priori SG, Napolitano C. How really rare are rare diseases?: the intriguing case of independent compound mutations in the long QT syndrome. J Cardiovasc Electrophysiol 2004; 14:1120-1. [PMID: 14521668 DOI: 10.1046/j.1540-8167.2003.03339.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Peter J Schwartz
- Department of Cardiology, IRCCS Policlinico S. Matteo, Pavia, Italy.
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Anson BD, Ackerman MJ, Tester DJ, Will ML, Delisle BP, Anderson CL, January CT. Molecular and functional characterization of common polymorphisms in HERG (KCNH2) potassium channels. Am J Physiol Heart Circ Physiol 2004; 286:H2434-41. [PMID: 14975928 DOI: 10.1152/ajpheart.00891.2003] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Long QT syndrome (LQTS) is a cardiac repolarization disorder that can lead to arrhythmias and sudden death. Chromosome 7-linked inherited LQTS (LQT2) is caused by mutations in human ether-a-go-go-related gene (HERG; KCNH2), whereas drug-induced LQTS is caused primarily by HERG channel block. Many common polymorphisms are functionally silent and have been traditionally regarded as benign and without physiological consequence. However, the identification of common nonsynonymous single nucleotide polymorphisms (nSNPs; i.e., amino-acid coding variants) with functional phenotypes in the SCN5A Na(+) channel and MiRP1 K(+) channel beta-subunit have challenged this viewpoint. In this report, we test the hypothesis that common missense HERG polymorphisms alter channel physiology. Comprehensive mutational analysis of HERG was performed on genomic DNA derived from a population-based cohort of sudden infant death syndrome and two reference allele cohorts derived from 100 African American and 100 Caucasian individuals. Amino acid-encoding variants were considered common polymorphisms if they were present in at least two of the three study cohorts with an allelic frequency >0.5%. Four nSNPs were identified: K897T, P967L, R1047L, and Q1068R. Wild-type (WT) and polymorphic channels were heterologously expressed in human embryonic kidney cells, and biochemical and voltage-clamp techniques were used to characterize their functional properties. All channel types were processed similarly, but several electrophysiological differences were identified: 1) K897T current density was lower than the other polymorphic channels; 2) K897T channels activated at more negative potentials than WT and R1047L; 3) K897T and Q1068R channels inactivated and recovered from inactivation faster than WT, P967L, and R1047L channels; and 4) K897T channels showed subtle differences compared with WT channels when stimulated with an action potential waveform. In contrast to K897T and Q1068R channels, P967L and R1047L channels were electrophysiologically indistinguishable from WT channels. All HERG channels had similar sensitivity to block by cisapride. Therefore, some HERG polymorphic channels are electrophysiologically different from WT channels.
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Affiliation(s)
- Blake D Anson
- Department of Medicine, University of Wisconsin, 1300 University Ave., Madison, WI 53711, USA.
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Kobori A, Sarai N, Shimizu W, Nakamura Y, Murakami Y, Makiyama T, Ohno S, Takenaka K, Ninomiya T, Fujiwara Y, Matsuoka S, Takano M, Noma A, Kita T, Horie M. Additional Gene Variants Reduce Effectiveness of Beta-Blockers in the LQT1 Form of Long QT Syndrome. J Cardiovasc Electrophysiol 2004; 15:190-9. [PMID: 15028050 DOI: 10.1046/j.1540-8167.2004.03212.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
INTRODUCTION Beta-blockers are widely used to prevent the lethal cardiac events associated with the long QT syndrome (LQTS), especially in KCNQ1-related LQTS (LQT1) patients. Some LQT1 patients, however, are refractory to this therapy. METHODS AND RESULTS Eighteen symptomatic LQTS patients (12 families) were genetically diagnosed as having heterozygous KCNQ1 variants and received beta-blocker therapy. Cardiac events recurred in 4 members (3 families) despite continued therapy during mean follow-up of 70 months. Three of these patients (2 families) had the same mutation [A341V (KCNQ1)]; and the other had R243H (KCNQ1). The latter patient took aprindine, which seemed to be responsible for the event. By functional assay using a heterologous mammalian expression system, we found that A341V (KCNQ1) is a loss-of-function type mutation (not dominant negative). Further genetic screening revealed that one A341V (KCNQ1) family cosegregated with S706C (KCNH2) and another with G144S (KCNJ2). Functional assay of the S706C (KCNH2) mutation was found to reduce the current density of expressed heterozygous KCNH2 channels with a positive shift (+8 mV) of the activation curve. Action potential simulation study was conducted based on the KYOTO model to estimate the influence of additional gene modifiers. In both models mimicking LQT1 plus 2 and LQT1 plus 7, the incidence of early afterdepolarization was increased compared with the LQT1 model under the setting of beta-adrenergic stimulation. CONCLUSION Multiple mutations in different LQTS-related genes may modify clinical characteristics. Expanded gene survey may be required in LQT1 patients who are resistant to beta-blocker therapy.
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Affiliation(s)
- Atsushi Kobori
- Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
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