151
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Calcium channel blocker and adenosine triphosphate terminate bidirectional ventricular tachycardia in a patient with Andersen-Tawil syndrome. Heart Rhythm 2007; 5:498-9. [PMID: 18313615 DOI: 10.1016/j.hrthm.2007.12.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2007] [Indexed: 11/21/2022]
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152
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Ryan AM, Matthews E, Hanna MG. Skeletal-muscle channelopathies: periodic paralysis and nondystrophic myotonias. Curr Opin Neurol 2007; 20:558-63. [PMID: 17885445 DOI: 10.1097/wco.0b013e3282efc16c] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
PURPOSE OF REVIEW To provide a current review of clinical phenotypes, genetics, molecular pathophysiology, and electro-diagnostic testing strategies of periodic paralysis and nondystrophic myotonias. RECENT FINDINGS The number of pathogenic mutations causing periodic paralysis and nondystrophic myotonias continues to increase. Important insight into the molecular pathogenesis of muscle sodium channelopathies has been revealed by the finding of 'leaky' closed sodium channels. Previously, alterations in sodium-channel activation or inactivation have been identified as important disease mechanisms. The recent discovery that substitutions of key arginine residues in the voltage-sensing segment of the channel may lead to a 'pore leak' when the channel is closed suggests a new mechanism. Since similar mutations exist in corresponding positions of other channels, this mechanism may apply to other channel diseases. The recognition of different electrophysiological patterns that are specific to muscle ion-channel genotypes will be useful in diagnosis and in guiding genetic testing. Recent studies demonstrate that magnetic resonance imaging may be used to detect intramuscular accumulation of sodium during episodes of weakness. SUMMARY Recent advances have refined our ability to make a precise molecular diagnosis in muscle channelopathies. The description of a pore leak with voltage-sensor mutations may represent a new disease mechanism.
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Affiliation(s)
- Aisling M Ryan
- MRC Centre for Neuromuscular Disease, Department of Molecular Neuroscience, Institute of Neurology, University College London, London, UK
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153
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Tani Y, Miura D, Kurokawa J, Nakamura K, Ouchida M, Shimizu K, Ohe T, Furukawa T. T75M-KCNJ2 mutation causing Andersen–Tawil syndrome enhances inward rectification by changing Mg2+ sensitivity. J Mol Cell Cardiol 2007; 43:187-96. [PMID: 17582433 DOI: 10.1016/j.yjmcc.2007.05.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2006] [Revised: 04/04/2007] [Accepted: 05/04/2007] [Indexed: 10/23/2022]
Abstract
Andersen-Tawil syndrome (ATS) is a multisystem inherited disease exhibiting periodic paralysis, cardiac arrhythmias, and dysmorphic features. In this study, we characterized the KCNJ2 channels with an ATS mutation (T75M) which is associated with cardiac phenotypes of bi-directional ventricular tachycardia, syncope, and QT(c) prolongation. Confocal imaging of GFP-KCNJ2 fusion proteins showed that the T75M mutation impaired membrane localization of the channel protein, which was restored by co-expression of WT channels with T75M channels. Whole-cell patch-clamp experiments in CHO-K1 cells showed that the T75M mutation produced a loss-of-function of the channel. When both WT and the T75M were co-expressed, the T75M mutation showed dominant-negative effects on inward rectifier K+ current densities, with prominent suppression of outward currents at potentials between 0 mV and +80 mV over the E(K). Inside-out patch experiments in HEK293T cells revealed that co-expression of WT and the T75M channels enhanced voltage-dependent block of the channels by internal Mg2+, resulting in enhanced inward rectification at potentials 50 mV more positive than the E(K). We suggest that the T75M mutation causes dominant-negative suppression of the co-expressed WT KCNJ2 channels. In addition, the T75M mutation caused alteration of gating kinetics of the mutated KCNJ2 channels, i.e., increased sensitivity to intracellular Mg2+ and resultant enhancement of inward rectification. The data presented suggest that the mutation may influence clinical features, but it does not directly show this.
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Affiliation(s)
- Yoshinori Tani
- Department of Bio-Informational Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, 2-3-10 Kandasurugadai, Chiyoda-ku, Tokyo 101-0062, Japan
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154
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Medeiros-Domingo A, Iturralde-Torres P, Ackerman MJ. Clínica y genética en el síndrome de QT largo. Rev Esp Cardiol 2007. [DOI: 10.1157/13108280] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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155
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Garcia-Touchard A, Somers VK, Kara T, Nykodym J, Shamsuzzaman A, Lanfranchi P, Ackerman MJ. Ventricular ectopy during REM sleep: implications for nocturnal sudden cardiac death. ACTA ACUST UNITED AC 2007; 4:284-8. [PMID: 17457352 PMCID: PMC3332547 DOI: 10.1038/ncpcardio0877] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2006] [Accepted: 01/05/2007] [Indexed: 11/09/2022]
Abstract
BACKGROUND A young adult female presented with syncope and periodic weakness. A 12-lead electrocardiogram showed frequent premature ventricular contractions and prolonged QU interval. Repetitive runs of nonsustained ventricular tachycardia were recorded at night. INVESTIGATIONS Electromyography, muscle biopsy, MRI, echocardiography, exercise stress testing using Bruce protocol with microvolt T-wave alternans testing, 24 h Holter monitoring, electrophysiological testing and examination of the effects of sleep and sleep stage on the patient's ventricular arrhythmias. DIAGNOSIS Type 1 Andersen-Tawil syndrome, (also known as type 7 long QT syndrome). Severe ventricular arrhythmia was observed, predominantly during rapid eye movement sleep. We speculate that the autonomic instability present during rapid eye movement sleep precipitates increasing vulnerability to sleep-related ventricular tachycardia. MANAGEMENT Beta-blocker therapy alone, subsequently combined with mexiletine treatment.
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Affiliation(s)
| | | | | | | | | | | | - Michael J Ackerman
- Correspondence Mayo Clinic College of Medicine, Mayo Clinic Windland Smith Rice Sudden Death Genomics Laboratory, Guggenheim 501, 200 First Street SW, Rochester, MN 55905, USA
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156
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Abstract
Andersen-Tawil syndrome (ATS) is characterized by periodic paralysis, cardiac arrhythmias, and distinct facial and skeletal features. The majority of patients with ATS (ATS1) have point mutations in the KCNJ2 gene, which encodes the inward-rectifying potassium channel known as Kir2.1. The skeletal muscle and cardiac symptoms are accounted for, in most cases, by a dominant negative effect of the mutations on potassium channel current, resulting in prolonged depolarization of the action potential. Mechanisms of disruption of channel function include abnormal trafficking and assembly of second messengers such as phosphatidylinositol 4,5-bisphosphate, abnormal gating of the channel, and incorrect folding of the Kir2.1 protein. Less apparent is the mechanism by which these mutations account for the typical facial and skeletal abnormalities. The concomitant involvement of cardiac and skeletal muscle in ATS poses unique treatment and management challenges. Because of differences in cardiac and skeletal muscle physiology, drugs that may have a beneficial effect on cardiac function may have a detrimental effect on skeletal muscle and vice versa. We review the clinical, laboratory, and genetic features of this disorder with particular emphasis on treatment and management.
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Affiliation(s)
- Valeria Sansone
- Department of Neurology, University of Milan, IRCCS Policlinico San Donato, Milan, Italy 20097.
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157
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Electrophysiologic characteristics of an Andersen syndrome patient with KCNJ2 mutation. Heart Rhythm 2007; 4:512-5. [DOI: 10.1016/j.hrthm.2006.10.030] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2006] [Accepted: 10/30/2006] [Indexed: 11/19/2022]
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158
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Jurkat-Rott K, Lehmann-Horn F. Genotype-phenotype correlation and therapeutic rationale in hyperkalemic periodic paralysis. Neurotherapeutics 2007; 4:216-24. [PMID: 17395131 DOI: 10.1016/j.nurt.2007.02.001] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Familial hyperkalemic periodic paralysis (PP) is a dominantly inherited muscle disease characterized by attacks of flaccid weakness and intermittent myotonia. Some patients experience muscle stiffness that is aggravated by cold and exercise, bordering on the diagnosis of paramyotonia congenita. Hyperkalemic PP and paramyotonia congenita are allelic diseases caused by gain-of-function mutations of the skeletal muscle sodium channel, Nav1.4, which is essential for the generation of skeletal muscle action potentials. In this review, the functional and clinical consequences of the mutations and therapeutic strategies are reported and the differential diagnoses discussed. Also, the question is addressed of whether hyperkalemic PP is truly a different entity than normokalemic PP. Additionally, the differential diagnosis of Andersen-Tawil syndrome in which hyperkalemic PP attacks may occur will be briefly introduced. Last, because hyperkalemic PP has been described to be associated with an R83H mutation of a MiRP2 potassium channel subunit, evidence refuting disease-causality in this case will be discussed.
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159
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Extramiana F. Screening for KCNJ2 mutations: The physician’s perspective. Heart Rhythm 2007; 4:330-1. [PMID: 17341398 DOI: 10.1016/j.hrthm.2006.11.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/09/2006] [Indexed: 11/28/2022]
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160
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Heidbüchel H, Corrado D, Biffi A, Hoffmann E, Panhuyzen-Goedkoop N, Hoogsteen J, Delise P, Hoff PI, Pelliccia A. Recommendations for participation in leisure-time physical activity and competitive sports of patients with arrhythmias and potentially arrhythmogenic conditions. Part II: ventricular arrhythmias, channelopathies and implantable defibrillators. ACTA ACUST UNITED AC 2007; 13:676-86. [PMID: 17001205 DOI: 10.1097/01.hjr.0000239465.26132.29] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
This consensus paper on behalf of the Study Group on Sports Cardiology of the European Society of Cardiology follows a previous one on guidelines for sports participation in competitive and recreational athletes with supraventricular arrhythmias and pacemakers. The question of imminent life-threatening arrhythmias is especially relevant when some form of ventricular rhythm disorder is documented, or when the patient is diagnosed to have inherited a pro-arrhythmogenic disorder. Frequent ventricular premature beats or nonsustained ventricular tachycardia may be a hallmark of underlying pathology and increased risk. Their finding should prompt a thorough cardiac evaluation, including both imaging modalities and electrophysiological techniques. This should allow distinguishing idiopathic rhythm disorders from underlying disease that carries a more ominous prognosis. Recommendations on sports participation in inherited arrhythmogenic conditions and asymptomatic gene carriers are also discussed: congenital and acquired long QT syndrome, short QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, arrhythmogenic right ventricular cardiomyopathy and other familial electrical disease of unknown origin. If an implantable cardioverter defibrillator is indicated, it is no substitute for the guidelines relating to the underlying pathology. Moreover, some particular recommendations for patients/athletes with an implantable cardioverter defibrillator are to be observed.
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Affiliation(s)
- Hein Heidbüchel
- Cardiology-Electrophysiology, University Hospital Gasthuisberg, Leuven, Belgium.
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161
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Poelzing S, Veeraraghavan R. Heterogeneous ventricular chamber response to hypokalemia and inward rectifier potassium channel blockade underlies bifurcated T wave in guinea pig. Am J Physiol Heart Circ Physiol 2007; 292:H3043-51. [PMID: 17307991 DOI: 10.1152/ajpheart.01312.2006] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It was previously demonstrated that transmural electrophysiological heterogeneities can inscribe the ECG T wave. However, the bifurcated T wave caused by loss of inward rectifier potassium current (I(K1)) function is not fully explained by transmural heterogeneities. Since right ventricular (RV) guinea pig myocytes have significantly lower I(K1) than left ventricular (LV) myocytes, we hypothesized that the complex ECG can be inscribed by heterogeneous chamber-specific responses to hypokalemia and partial I(K1) blockade. Ratiometric optical action potentials were recorded from the epicardial surface of the RV and LV. BaCl(2) (10 micromol/l) was perfused to partially block I(K1) in isolated guinea pig whole heart preparations. BaCl(2) or hypokalemia alone significantly increased RV basal (RV(B)) action potential duration (APD) by approximately 30% above control compared with LV apical (LV(A)) APD (14%, P<0.05). In the presence of BaCl(2), 2 mmol/l extracellular potassium (hypokalemia) further increased RV(B) APD to a greater extent (31%) than LV(A) APD (19%, P<0.05) compared with BaCl(2) perfusion alone. Maximal dispersion between RV(B) and LV(A) APD increased by 105% (P<0.05), and the QT interval prolonged by 55% (P<0.05) during hypokalemia and BaCl(2). Hypokalemia and BaCl(2) produced an ECG with a double repolarization wave. The first wave (QT1) corresponded to selective depression of apical LV plateau potentials, while the second wave (QT2) corresponded to the latest repolarizing RV(B) myocytes. These data suggest that final repolarization is more sensitive to extracellular potassium changes in regions with reduced I(K1), particularly when I(K1) availability is reduced. Furthermore, underlying I(K1) heterogeneities can potentially contribute to the complex ECG during I(K1) loss of function and hypokalemia.
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Affiliation(s)
- Steven Poelzing
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112-5000, USA.
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162
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Peters S, Schulze-Bahr E, Etheridge SP, Tristani-Firouzi M. Sudden cardiac death in Andersen-Tawil syndrome. Europace 2007; 9:162-6. [PMID: 17272325 DOI: 10.1093/europace/eul188] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Andersen-Tawil syndrome (ATS) is an autosomal dominant or sporadic disorder characterized by periodic paralysis, dysmorphic features, and ventricular arrhythmias. Although ventricular tachycardia burden is quite high sudden cardiac death in ATS is rare. We describe a case with sudden cardiac death due to electrical storm a few days after ICD implantation in KCNJ2 mutation-negative ATS.
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Affiliation(s)
- Stefan Peters
- Klinikum Dorothea Christiane Erxleben Quedlinburg, Academic Teaching Hospital of the University Hospital Magdeburg, Innere Medizin II-Kardiologie, Ditfurter Weg 24, 06484 Quedlinburg, Germany.
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163
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Seemann G, Sachse FB, Weiss DL, Ptácek LJ, Tristani-Firouzi M. Modeling of IK1 mutations in human left ventricular myocytes and tissue. Am J Physiol Heart Circ Physiol 2007; 292:H549-59. [PMID: 16936001 DOI: 10.1152/ajpheart.00701.2006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Elucidation of the cellular basis of arrhythmias in ion channelopathy disorders is complicated by the inherent difficulties in studying human cardiac tissue. Thus we used a computer modeling approach to study the mechanisms of cellular dysfunction induced by mutations in inward rectifier potassium channel (Kir)2.1 that cause Andersen-Tawil syndrome (ATS). ATS is an autosomal dominant disorder associated with ventricular arrhythmias that uncommonly degenerate into the lethal arrhythmia torsade de pointes. We simulated the cellular and tissue effects of a potent disease-causing mutation D71V Kir2.1 with mathematical models of human ventricular myocytes and a bidomain model of transmural conduction. The D71V Kir2.1 mutation caused significant action potential duration prolongation in subendocardial, midmyocardial, and subepicardial myocytes but did not significantly increase transmural dispersion of repolarization. Simulations of the D71V mutation at shorter cycle lengths induced stable action potential alternans in midmyocardial, but not subendocardial or subepicardial cells. The action potential alternans was manifested as an abbreviated QRS complex in the transmural ECG, the result of action potential propagation failure in the midmyocardial tissue. In addition, our simulations of D71V mutation recapitulate several key ECG features of ATS, including QT prolongation, T-wave flattening, and QRS widening. Thus our modeling approach faithfully recapitulates several features of ATS and provides a mechanistic explanation for the low frequency of torsade de pointes arrhythmia in ATS.
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Affiliation(s)
- Gunnar Seemann
- Nora Eccles Harrison Cardiovascular Research and Training Institute, Univ. of Utah, Salt Lake City, UT 84108, USA.
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164
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Abstract
At present, cardiac rhythm disorders such as sick sinus syndrome (SSS) or AV nodal block (AVB) are usually treated by electronic pacemakers. These devices have significant shortcomings, including lack of autonomic modulation, and the need for repetitive procedures for battery replacement or lead repositioning. Biological pacemakers as replacement or complement to electronic pacemakers have been the subject of increasing research interest. This research has resulted in many encouraging preclinical studies. Various approaches in the field of gene and cell therapy have been developed by different groups and this combined effort makes it increasingly realistic that this therapy will eventually find its way to clinical applicability. (Neth Heart J 2007;15:318-22.).
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Affiliation(s)
- G.J.J. Boink
- Heart Failure Research Centre, Academic Medical Centre,
University of Amsterdam, Amsterdam, and Interuniversity Cardiology Institute
Netherlands, Utrecht, the Netherlands
| | - J. Seppen
- Liver Centre, Academic Medical Centre, University of
Amsterdam, Amsterdam, the Netherlands
| | - J.M.T. de Bakker
- Heart Failure Research Centre, Academic Medical Centre,
University of Amsterdam, Amsterdam, and Interuniversity Cardiology Institute
Netherlands, Utrecht, the Netherlands
| | - H.L. Tan
- Heart Failure Research Centre, and Department of
Cardiology, Academic Medical Centre, University of Amsterdam, Amsterdam, the
Netherlands
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165
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Schwartz PJ, Crotti L. Can a Message From the Dead Save Lives?⁎⁎Editorials published in the Journal of the American College of Cardiologyreflect the views of the authors and do not necessarily represent the views of JACCor the American College of Cardiology. J Am Coll Cardiol 2007; 49:247-9. [PMID: 17222737 DOI: 10.1016/j.jacc.2006.10.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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166
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Flecainide for recurrent malignant ventricular arrhythmias in two siblings with Andersen-Tawil syndrome. Heart Rhythm 2006; 4:508-11. [PMID: 17399642 DOI: 10.1016/j.hrthm.2006.12.031] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/28/2006] [Accepted: 12/13/2006] [Indexed: 11/25/2022]
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167
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Ma D, Tang XD, Rogers TB, Welling PA. An andersen-Tawil syndrome mutation in Kir2.1 (V302M) alters the G-loop cytoplasmic K+ conduction pathway. J Biol Chem 2006; 282:5781-9. [PMID: 17166852 DOI: 10.1074/jbc.m608776200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Loss-of-function mutations in the inward rectifier potassium channel, Kir2.1, cause Andersen-Tawil syndrome (ATS-1), an inherited disorder of periodic paralysis and ventricular arrhythmias. Here, we explore the mechanism by which a specific ATS-1 mutation (V302M) alters channel function. Val-302 is located in the G-loop, a structure that is believed to form a flexible barrier for potassium permeation at the apex of the cytoplasmic pore. Consistent with a role in stabilizing the G-loop in an open conformation, we found the V302M mutation specifically renders the channel unable to conduct potassium without altering subunit assembly or attenuating cell surface expression. As predicted by the position of the Val-302 side chain in the crystal structure, amino acid substitution analysis revealed that channel activity and phosphatidylinositol 4,5-bisphosphate (PIP2) sensitivity are profoundly sensitive to alterations in the size, shape, and hydrophobicity of side chains at the Val-302 position. The observations establish that the Val-302 side chain is a critical determinant of potassium conduction through the G-loop. Based on our functional studies and the cytoplasmic domain crystal structure, we suggest that Val-302 may influence PIP2 gating indirectly by translating PIP2 binding to conformational changes in the G-loop pore.
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Affiliation(s)
- Donghui Ma
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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168
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Eckhardt LL, Farley AL, Rodriguez E, Ruwaldt K, Hammill D, Tester DJ, Ackerman MJ, Makielski JC. KCNJ2 mutations in arrhythmia patients referred for LQT testing: a mutation T305A with novel effect on rectification properties. Heart Rhythm 2006; 4:323-9. [PMID: 17341397 PMCID: PMC1868697 DOI: 10.1016/j.hrthm.2006.10.025] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/11/2006] [Accepted: 10/25/2006] [Indexed: 11/21/2022]
Abstract
BACKGROUND Loss-of-function mutations in the KCNJ2 cause approximately 50% of Andersen-Tawil Syndrome (ATS) characterized by a classic triad of periodic paralysis, ventricular arrhythmia, and dysmorphic features. Do KCNJ2 mutations occur in patients lacking this triad and lacking a family history of ATS? OBJECTIVES The purpose of this study was to identify and characterize mutations in the KCNJ2-encoded inward rectifier potassium channel Kir2.1 from patients referred for genetic arrhythmia testing. METHODS Mutational analysis of KCNJ2 was performed for 541 unrelated patients. The mutations were made in wild type (WT) and expressed in COS-1 cells and voltage clamped for ion currents. RESULTS Three novel missense mutations (R67Q, R85W, and T305A) and one known mutation (T75M) were identified in 4/249 (1.6%) patients genotype-negative for other known arrhythmia genes with overall incidence 4/541 (0.74%). They had prominent U-waves, marked ventricular ectopy, and polymorphic ventricular tachycardia but no facial/skeletal abnormalities. Periodic paralysis was present in only one case. Outward current was decreased to less than 5% of WT for all mutants expressed alone. Co-expression with WT (simulating heterozygosity) caused a marked dominant negative effect for T75M and R82W, no dominant negative effect for R67Q, and a novel selective enhancement of inward rectification for T305A. CONCLUSIONS KCNJ2 loss of function mutations were found in approximately 1% of patients referred for genetic arrhythmia testing that lacked criteria for ATS. Characterization of three new mutations identified a novel dominant negative effect selectively reducing outward current for T305A. These results extend the range of clinical phenotype and molecular phenotype associated with KCNJ2 mutations.
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Affiliation(s)
- Lee L. Eckhardt
- Department of Medicine (Cardiovascular Medicine), University of Wisconsin, Madison, WI
| | - Amanda L. Farley
- Department of Medicine (Cardiovascular Medicine), University of Wisconsin, Madison, WI
| | - Esther Rodriguez
- Departments of Medicine, Pediatrics, and Molecular Pharmacology, Divisions of Cardiovascular Diseases and Pediatric Cardiology, Mayo Clinic College of Medicine, Rochester, MN
| | - Karen Ruwaldt
- Department of Medicine (Cardiovascular Medicine), University of Wisconsin, Madison, WI
| | - Daniel Hammill
- Departments of Medicine, Pediatrics, and Molecular Pharmacology, Divisions of Cardiovascular Diseases and Pediatric Cardiology, Mayo Clinic College of Medicine, Rochester, MN
| | - David J. Tester
- Departments of Medicine, Pediatrics, and Molecular Pharmacology, Divisions of Cardiovascular Diseases and Pediatric Cardiology, Mayo Clinic College of Medicine, Rochester, MN
| | - Michael J. Ackerman
- Departments of Medicine, Pediatrics, and Molecular Pharmacology, Divisions of Cardiovascular Diseases and Pediatric Cardiology, Mayo Clinic College of Medicine, Rochester, MN
| | - Jonathan C. Makielski
- Department of Medicine (Cardiovascular Medicine), University of Wisconsin, Madison, WI
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169
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Schoonderwoerd BA, Wiesfeld ACP, Wilde AAM, van den Heuvel F, Van Tintelen JP, van den Berg MP, Van Veldhuisen DJ, Van Gelder IC. A family with Andersen-Tawil syndrome and dilated cardiomyopathy. Heart Rhythm 2006; 3:1346-50. [PMID: 17074642 DOI: 10.1016/j.hrthm.2006.07.021] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/26/2006] [Accepted: 07/17/2006] [Indexed: 10/24/2022]
Affiliation(s)
- Bas A Schoonderwoerd
- Department of Cardiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
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170
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Boink GJJ, Seppen J, de Bakker JMT, Tan HL. Gene therapy to create biological pacemakers. Med Biol Eng Comput 2006; 45:167-76. [PMID: 17048028 DOI: 10.1007/s11517-006-0112-7] [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] [Received: 03/26/2006] [Accepted: 09/04/2006] [Indexed: 11/28/2022]
Abstract
Old age and a variety of cardiovascular disorders may disrupt normal sinus node function. Currently, this is successfully treated with electronic pacemakers, which, however, leave room for improvement. During the past decade, different strategies to initiate pacemaker function by gene therapy were developed. In the search for a biological pacemaker, various approaches were explored, including beta(2)-adrenergic receptor overexpression, down regulation of the inward rectifier current, and overexpression of the pacemaker current. The most recent advances include overexpression of bioengineered ion channels and genetically modified stem cells. This review considers the strengths and the weaknesses of the different approaches and discusses some of the different viral vectors currently used.
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Affiliation(s)
- Gerard J J Boink
- Department of Clinical and Experimental Cardiology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands
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171
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Abstract
PURPOSE OF REVIEW Dramatic advances have been made in understanding of both the genetics and the phenotypic expression of congenital long QT syndrome. This paper reviews recent clinically relevant literature. RECENT FINDINGS Long QT syndrome is one of the leading causes of sudden cardiac death. This syndrome, once diagnosed by a clinical profile, has been more clearly defined by specific gene defects causing ion channel abnormalities in the beating heart. Genetic testing for long QT syndrome, once available only through research laboratories, is now commercially available. Diagnosis, risk assessment, and management are increasingly being guided by gene-specific diagnoses. In a family with suspected disease, the genetic test will determine the defect in as many as 75% of subjects. Once the diagnosis is made, the mainstay of therapy continues to be beta-blockers. Implantable cardioverter-defibrillators are indicated in patients at high risk for malignant arrhythmias. SUMMARY Long QT syndrome is one of the first cardiovascular diseases to see the dramatic changes that bench research can bring to the clinical arena. Future research is needed to determine the gene defect in the remaining 25% of patients with suspected long QT syndrome and in risk stratification.
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Affiliation(s)
- Kathryn K Collins
- University of California-San Francisco, 521 Parnassus, San Francisco, CA 94143, USA.
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172
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Zipes DP, Camm AJ, Borggrefe M, Buxton AE, Chaitman B, Fromer M, Gregoratos G, Klein G, Moss AJ, Myerburg RJ, Priori SG, Quinones MA, Roden DM, Silka MJ, Tracy C, Smith SC, Jacobs AK, Adams CD, Antman EM, Anderson JL, Hunt SA, Halperin JL, Nishimura R, Ornato JP, Page RL, Riegel B, Priori SG, Blanc JJ, Budaj A, Camm AJ, Dean V, Deckers JW, Despres C, Dickstein K, Lekakis J, McGregor K, Metra M, Morais J, Osterspey A, Tamargo JL, Zamorano JL. ACC/AHA/ESC 2006 guidelines for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: a report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death). J Am Coll Cardiol 2006; 48:e247-346. [PMID: 16949478 DOI: 10.1016/j.jacc.2006.07.010] [Citation(s) in RCA: 867] [Impact Index Per Article: 48.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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173
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Efremidis M, Pappas LK, Sideris A, Letsas KP, Gavrielatos GD, Kardaras F. Swimming-triggered aborted sudden cardiac death in a patient with Andersen–Tawil syndrome. Int J Cardiol 2006; 112:e45-7. [PMID: 16859779 DOI: 10.1016/j.ijcard.2006.02.028] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/24/2005] [Accepted: 02/24/2006] [Indexed: 10/24/2022]
Abstract
In this report we describe the case of a 42-year-old woman who experienced an episode of near drowning during recreational swimming. A diagnosis of Andersen-Tawil syndrome was made based on the patient's dysmorphic features, characteristic T-U-wave patterns and ventricular arrhythmias. To our knowledge, this is the first report of a swimming-triggered cardiac event in a patient with Andersen-Tawil syndrome.
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174
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Zipes DP, Camm AJ, Borggrefe M, Buxton AE, Chaitman B, Fromer M, Gregoratos G, Klein G, Moss AJ, Myerburg RJ, Priori SG, Quinones MA, Roden DM, Silka MJ, Tracy C, Smith SC, Jacobs AK, Adams CD, Antman EM, Anderson JL, Hunt SA, Halperin JL, Nishimura R, Ornato JP, Page RL, Riegel B, Blanc JJ, Budaj A, Dean V, Deckers JW, Despres C, Dickstein K, Lekakis J, McGregor K, Metra M, Morais J, Osterspey A, Tamargo JL, Zamorano JL. ACC/AHA/ESC 2006 Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death: a report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (writing committee to develop Guidelines for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death): developed in collaboration with the European Heart Rhythm Association and the Heart Rhythm Society. Circulation 2006; 114:e385-484. [PMID: 16935995 DOI: 10.1161/circulationaha.106.178233] [Citation(s) in RCA: 807] [Impact Index Per Article: 44.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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175
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176
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Sung RJ, Wu SN, Wu JS, Chang HD, Luo CH. Electrophysiological mechanisms of ventricular arrhythmias in relation to Andersen-Tawil syndrome under conditions of reduced IK1: a simulation study. Am J Physiol Heart Circ Physiol 2006; 291:H2597-605. [PMID: 16877549 DOI: 10.1152/ajpheart.00393.2006] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Patients with Andersen-Tawil syndrome (ATS) mostly have mutations on the KCNJ2 gene, producing loss of function or dominant-negative suppression of the inward rectifier K(+) channel Kir2.1. However, clinical manifestations of ATS including dysmorphic features, periodic paralysis (hypo-, hyper-, or normokalemic), long QT, and ventricular arrhythmias (VAs) are considerably variable. Using a modified dynamic Luo-Rudy simulation model of cardiac ventricular myocytes, we attempted to elucidate mechanisms of VA in ATS by analyzing effects of the inward rectifier K(+) channel current (I(K1)) on the action potential (AP). During pacing at 1.0 Hz with extracellular K(+) concentration ([K(+)](o)) at 4.5 mM, a stepwise 10% reduction of Kir2.1 channel conductance progressively prolonged the terminal repolarization phase of the AP along with gradual depolarization of the resting membrane potential (RMP). At 90% reduction, early afterdepolarizations (EADs) became inducible and RMP was depolarized to -52.0 mV (control: -89.8 mV), followed by emergence of spontaneous APs. Both EADs and spontaneous APs were facilitated by a decrease in [K(+)](o) and suppressed by an increase in [K(+)](o). Simulated beta-adrenergic stimulation enhanced delayed afterdepolarizations (DADs) and could also facilitate EADs as well as spontaneous APs in the setting of low [K(+)](o) and reduced Kir2.1 channel conductance. In conclusion, the spectrum of VAs in ATS may include 1) triggered activity mediated by EADs and/or DADs and 2) abnormal automaticity manifested as spontaneous APs. These VAs can be aggravated by a decrease in [K(+)](o) and beta-adrenergic stimulation and may potentially induce torsade de pointes and cause sudden death. In patients with ATS, the hypokalemic form of periodic paralysis should have the highest propensity to VAs, especially during physical activity.
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MESH Headings
- Action Potentials/physiology
- Andersen Syndrome/genetics
- Andersen Syndrome/physiopathology
- Animals
- Arrhythmias, Cardiac/etiology
- Arrhythmias, Cardiac/physiopathology
- Calcium/metabolism
- Death, Sudden, Cardiac
- Electrocardiography
- Electrophysiology
- Guinea Pigs
- Hypokalemic Periodic Paralysis/physiopathology
- Membrane Potentials/physiology
- Models, Theoretical
- Mutation/genetics
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/pathology
- Myocytes, Cardiac/physiology
- Potassium/metabolism
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/physiology
- Receptors, Adrenergic, beta/physiology
- Ventricular Dysfunction/etiology
- Ventricular Dysfunction/physiopathology
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Affiliation(s)
- Ruey J Sung
- Dept. of Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan 704.
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177
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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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178
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179
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Ackerman MJ. Genotype-phenotype relationships in congenital long QT syndrome. J Electrocardiol 2006; 38:64-8. [PMID: 16226077 DOI: 10.1016/j.jelectrocard.2005.06.018] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2005] [Accepted: 06/10/2005] [Indexed: 11/26/2022]
Affiliation(s)
- Michael J Ackerman
- Department of Medicine, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
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180
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Tsuboi M, Antzelevitch C. Cellular basis for electrocardiographic and arrhythmic manifestations of Andersen-Tawil syndrome (LQT7). Heart Rhythm 2006; 3:328-35. [PMID: 16500306 PMCID: PMC1474110 DOI: 10.1016/j.hrthm.2005.11.026] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2005] [Accepted: 11/23/2005] [Indexed: 10/25/2022]
Abstract
BACKGROUND Andersen-Tawil syndrome, a skeletal muscle syndrome associated with periodic paralysis and long QT intervals on the ECG, has been linked to defects in KCNJ2, the gene encoding for the inward rectifier potassium channel (I(K1).) OBJECTIVES The purpose of this study was to examine the cellular mechanisms underlying the ECG and arrhythmic manifestations of Andersen-Tawil syndrome. METHODS To investigate the effects of KCNJ2 loss-of-function mutations responsible for Andersen-Tawil syndrome, we used barium chloride (BaCl(2)) to inhibit I(K1) in arterially perfused wedge preparation. Transmembrane action potentials (APs) were simultaneously recorded from endocardial, midmyocardial, and epicardial cells, together with a transmural ECG. RESULTS BaCl(2) (1 to 30 microM) produced a concentration-dependent prolongation of the QT interval, secondary to a homogeneous prolongation of AP duration of the three cell types. QT interval was prolonged without an increase in transmural dispersion of repolarization (TDR). Low extracellular potassium (2.0 mM), isoproterenol (20-50 nM), and an abrupt increase in temperature (36 degrees C-39 degrees C) in the presence of 10 microM BaCl(2) did not significantly increase TDR but increased ectopic extrasystolic activity. Early afterdepolarizations were not observed under any condition. Spontaneous torsades de pointes arrhythmias were never observed, nor could they be induced with programmed electrical stimulation under any of the conditions studied. CONCLUSION Our results provide an understanding of why QT prolongation associated with Andersen-Tawil syndrome is relatively benign in the clinic and provide further support for the hypothesis that the increase in TDR, rather than QT interval, is responsible for development of torsades de pointes.
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Affiliation(s)
- Masato Tsuboi
- Masonic Medical Research Laboratory, 2150 Bleecker Street, Utica, NY 13501-1787, USA
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181
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182
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Yoon G, Oberoi S, Tristani-Firouzi M, Etheridge SP, Quitania L, Kramer JH, Miller BL, Fu YH, Ptácek LJ. Andersen-Tawil syndrome: Prospective cohort analysis and expansion of the phenotype. Am J Med Genet A 2006; 140:312-21. [PMID: 16419128 DOI: 10.1002/ajmg.a.31092] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Andersen-Tawil syndrome (ATS) is an autosomal dominant multisystem disorder characterized by developmental, cardiac, and neuromuscular abnormalities. Approximately 70% of patients have mutations in KCNJ2, resulting in dysfunction of the inward-rectifying potassium channel Kir2.1. Variable expression complicates the diagnosis of ATS, which in many cases, is not made until years after the first recognized symptom. To better define the distinctive clinical features of ATS and facilitate earlier diagnosis, we conducted a prospective, standardized evaluation of 10 subjects with confirmed KCNJ2 mutations. Detailed anthropometric, neurological, and cardiac evaluations were performed. Using this approach, we identified novel skeletal and dental findings and proposed additional diagnostic criteria for ATS dysmorphology.
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Affiliation(s)
- G Yoon
- Department of Pediatrics, Division of Medical Genetics, University of California, San Francisco, California 94143-0748, USA.
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183
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Abstract
The long QT syndrome (LQTS) is a genetic disorder responsible for many sudden deaths before age 20. The identification of several LQTS genes, all encoding cardiac ion channels, has had a major impact on the management strategy for both patients and family members. Genotype-guided therapy allows more effective individually tailored therapy. Therapeutic options, including beta-blockers, left cardiac sympathetic denervation, and implantable defibrillators are discussed for patients of known and of unknown genotype. The recent identification of modifier genes which amplify the effect of an LQTS mutation may change the approach to risk stratification.
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Affiliation(s)
- Peter J Schwartz
- Department of Cardiology, IRCCS Policlinico S. Matteo and University of Pavia, Pavia, Italy.
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184
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Venance SL, Cannon SC, Fialho D, Fontaine B, Hanna MG, Ptacek LJ, Tristani-Firouzi M, Tawil R, Griggs RC. The primary periodic paralyses: diagnosis, pathogenesis and treatment. ACTA ACUST UNITED AC 2005; 129:8-17. [PMID: 16195244 DOI: 10.1093/brain/awh639] [Citation(s) in RCA: 195] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Periodic paralyses (PPs) are rare inherited channelopathies that manifest as abnormal, often potassium (K)-sensitive, muscle membrane excitability leading to episodic flaccid paralysis. Hypokalaemic (HypoPP) and hyperkalaemic PP and Andersen-Tawil syndrome are genetically heterogeneous. Over the past decade mutations in genes encoding three ion channels, CACN1AS, SCN4A and KCNJ2, have been identified and account for at least 70% of the identified cases of PP and several allelic disorders. No prospective clinical studies have followed sufficiently large cohorts with characterized molecular lesions to draw precise conclusions. We summarize current knowledge of the clinical diagnosis, molecular genetics, genotype-phenotype correlations, pathophysiology and treatment in the PPs. We focus on unresolved issues including (i) Are there additional ion channel defects in cases without defined mutations? (ii) What is the mechanism for depolarization-induced weakness in Hypo PP? and finally (iii) Will detailed electrophysiological studies be able to correctly identify specific channel mutations? Understanding the pathophysiology of the potassium-sensitive PPs ought to reduce genetic complexity, allow subjects to be stratified during future clinical trials and increase the likelihood of observing true clinical effects. Ideally, therapy for the PPs will prevent attacks, avoid permanent weakness and improve quality of life. Moreover, understanding the skeletal muscle channelopathies will hopefully lead to insights into the more common central nervous system channel diseases such as migraine and epilepsy.
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Affiliation(s)
- S L Venance
- Department of Clinical Neurological Sciences, London Health Sciences Centre, London, ON, Canada.
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