Absence of calsequestrin 2 causes severe forms of catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare arrhythmogenic disorder characterized by syncopal events and sudden cardiac death at a young age during physical stress or emotion, in the absence of structural heart disease. We report the first nonsense mutations in the cardiac calsequestrin gene, CASQ2, in three CPVT families. The three mutations, a nonsense R33X, a splicing 532+1 G>A, and a 1-bp deletion, 62delA, are thought to induce premature stop codons. Two patients who experienced syncopes before the age of 7 years were homozygous carriers, suggesting a complete absence of calsequestrin 2. One patient was heterozygous for the stop codon and experienced syncopes from the age of 11 years. Despite the different mutations, there is little phenotypic variation of CPVT for the CASQ2 mutations. Of the 16 heterozygous carriers of these various mutations, 14 were devoid of clinical symptoms or ECG anomalies, whereas 2 of them had ventricular arrhythmias at ECG on exercise tests. In line with this, the diagnosis of the probands was difficult because of the absence of a positive family history. In conclusion, these additional three CASQ2 CPVT families suggest that CASQ2 mutations are more common than previously thought and produce a severe form of CPVT. The full text of this article is available at http://www.circresaha.org.     

Catecholaminergic Polymorphic Ventricular Tachycardia from Bedside to Bench and Beyond

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a primary electrical myocardial disease characterized by exercise- and stress-related ventricular tachycardia manifested as syncope and sudden death. The disease has a heterogeneous genetic basis, with mutations in the cardiac Ryanodine Receptor channel (RyR2) gene accounting for an autosomal-dominant form (CPVT1) in approximately 50% and mutations in the cardiac calsequestrin gene (CASQ2) accounting for an autosomal-recessive form (CPVT2) in up to 2% of CPVT cases. Both RyR2 and calsequestrin are important participants in the cardiac cellular calcium homeostasis.We review the physiology of the cardiac calcium homeostasis, including the cardiac excitation contraction coupling and myocyte calcium cycling. The pathophysiology of cardiac arrhythmias related to myocyte calcium handling and the effects of different modulators are discussed.The putative derangements in myocyte calcium homeostasis responsible for CPVT, as well as the clinical manifestations and therapeutic options available, are described.     

Molecular and electrophysiological bases of catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disorder characterized by adrenergically mediated polymorphic ventricular tachyarrhythmias. Genetic investigations have identified two variants of the disease: an autosomal dominant form associated with mutations in the gene encoding the cardiac ryanodine receptor (RyR2) and a recessive form associated with homozygous mutations in the gene encoding the cardiac isoform of calsequestrin (CASQ2). Functional characterization of mutations identified in the RyR2 and CASQ2 genes has demonstrated that CPVT are caused by derangements of the control of intracellular calcium. Investigations in a knock-in mouse model have shown that CPVT arrhythmias are initiated by delayed afterdepolarizations and triggered activity. In the present article, we review clinical and molecular understanding of CPVT and discuss the most recent approaches to develop novel therapeutic strategies for the disease.     

Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a highly lethal form of inherited arrhythmogenic disease characterized by adrenergically mediated polymorphic ventricular tachycardia. The mutations in cardiac ryanodine receptor and calsequestrin genes are responsible for the autosomal dominant and recessive variants of CPVT, respectively. The clinical presentation encompasses exercise- or emotion-induced syncopal events and a distinctive pattern of reproducible, stress-related, bidirectional ventricular tachycardia in the absence of both structural heart disease and a prolonged QT interval. The mortality rate in untreated individuals is 30-50% by age 40. Clinical evaluation by exercise stress testing and holter monitoring and genetic screening can facilitate early diagnosis. beta-adrenergic blockers are the most effective pharmacological treatment in controlling arrhythmias in CPVT patients, yet about 30% of patients still experience cardiac arrhythmias and eventually require an implantable cardioverter defibrillator.     

Guidelines for the diagnosis and management of Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND: Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is an inherited arrhythmia syndrome, characterised by polymorphic ventricular tachycardia induced by adrenergic stress. CPVT can be caused by mutations the cardiac ryanodine receptor gene (RYR2) or mutations in the cardiac calsequestrin gene CASQ2. Structural heart disease is usually absent and the baseline ECG is usually normal. Patients with CPVT often present with exercise- or emotion induced syncope, the first presentation can also be sudden cardiac death. MANAGEMENT: Besides removal of triggers treatment with beta blockers is currently a class I indication in clinically diagnosed patients. Beta blockage should be titrated up to an effective level. The addition of flecainide seems to be a promising approach in patients where arrhythmias are not completely suppressed by beta blockers. A cardioverter-defibrillator (ICD) or left cervical sympathetic denervation might be considered under special circumstances. Genetic counselling is recommended and all first degree relatives should be properly evaluated.     

Bidirectional ventricular tachycardia and fibrillation elicited in a knock-in mouse model carrier of a mutation in the cardiac ryanodine receptor

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited disease characterized by adrenergically mediated polymorphic ventricular tachycardia leading to syncope and sudden cardiac death. The autosomal dominant form of CPVT is caused by mutations in the RyR2 gene encoding the cardiac isoform of the ryanodine receptor. In vitro functional characterization of mutant RyR2 channels showed altered behavior on adrenergic stimulation and caffeine administration with enhanced calcium release from the sarcoplasmic reticulum. As of today no experimental evidence is available to demonstrate that RyR2 mutations can reproduce the arrhythmias observed in CPVT patients. We developed a conditional knock-in mouse model carrier of the R4496C mutation, the mouse equivalent to the R4497C mutations identified in CPVT families, to evaluate if the animals would develop a CPVT phenotype and if beta blockers would prevent arrhythmias. Twenty-six mice (12 wild-type (WT) and 14RyR(R4496C)) underwent exercise stress testing followed by epinephrine administration: none of the WT developed ventricular tachycardia (VT) versus 5/14 RyR(R4496C) mice (P=0.02). Twenty-one mice (8 WT, 8 RyR(R4496C), and 5 RyR(R4496C) pretreated with beta-blockers) received epinephrine and caffeine: 4/8 (50%) RyR(R4496C) mice but none of the WT developed VT (P=0.02); 4/5 RyR(R4496C) mice pretreated with propranolol developed VT (P=0.56 nonsignificant versus RyR(R4496C) mice). These data provide the first experimental demonstration that the R4496C RyR2 mutation predisposes the murine heart to VT and VF in response caffeine and/or adrenergic stimulation. Furthermore, the results show that analogous to what is observed in patients, beta adrenergic stimulation seems ineffective in preventing life-threatening arrhythmias.     

Spectrum and prevalence of cardiac ryanodine receptor (RyR2) mutations in a cohort of unrelated patients referred explicitly for long QT syndrome genetic testing.

BACKGROUND: Mutations in the RyR2-encoded cardiac ryanodine receptor/calcium release channel cause type 1 catecholaminergic polymorphic ventricular tachycardia (CPVT1). OBJECTIVES: Because CPVT and concealed long QT syndrome (LQTS) phenotypically mimic one other, we sought to determine the spectrum and prevalence of RyR2 mutations in a cohort of unrelated patients who were referred specifically for LQTS genetic testing. METHODS: Using denaturing high-performance liquid chromatography and direct DNA sequencing, targeted mutational analysis of 23 RyR2 exons previously implicated in CPVT1 was performed on genomic DNA from 269 unrelated patients (180 females, average age at diagnosis 24 +/- 17 years) who were referred to Mayo Clinic's Sudden Death Genomics Laboratory for LQTS genetic testing. Previously, comprehensive mutational analysis of the five LQTS-associated cardiac channel genes proved negative for this entire subset of patients now designated as "genotype-negative" LQTS referrals. RESULTS: Fifteen distinct RyR2 mutations (14 missense, 1 duplication/insertion, 12 novel) were found in 17 (6.3%) of 269 patients. None of these mutations were present in 400 reference alleles. Two mutations localized to the calstabin-2 (FKBP12.6) binding domain. Upon review of the clinical records, the referral diagnosis for all 17 patients was "atypical" or "borderline" LQTS. CONCLUSION: Putative pathogenic CPVT1-causing mutations in RyR2 were detected in 6% of unrelated, genotype-negative LQTS referrals. These findings suggest that CPVT may be underrecognized among physicians referring patients because of a suspected channelopathy. A diagnosis of "atypical LQTS" may warrant consideration of CPVT and analysis of RyR2 if the standard cardiac channel gene screen for LQTS is negative.     

Intravenous epinephrine infusion test in diagnosis of catecholaminergic polymorphic ventricular tachycardia

Epinephrine Infusion in Diagnosis of CPVT. Introduction: A test involving intravenous infusion of epinephrine has been proposed as a method alternative to exercise stress test in diagnosis of catecholaminergic polymorphic ventricular tachycardia (CPVT). We aimed at estimating the predictive value of intravenous epinephrine administration in CPVT patients with frequent exercise‐induced ventricular ectopy. Methods and Results: We recruited 81 subjects, including 25 CPVT‐linked ryanodine receptor 2 (RYR2) mutation carriers, 11 genetically undefined CPVT patients, and 45 unaffected family members. All subjects underwent a maximal exercise stress test and an intravenous epinephrine infusion test. Exercise stress test was positive in 25 (31%) patients including 14 of 25 (56%) established RYR2‐mutation carriers and all 11 (100%) genetically undefined CPVT patients. Epinephrine infusion induced arrhythmias in 3 (12%) RYR2‐mutation carriers, 4 (36%) genetically undefined CPVT patients, and 1 (2%) unaffected family member. A total of 18 exercise stress test positive patients did not respond to intravenous epinephrine administration, whereas only 1 epinephrine test responder had a normal exercise stress test. Thus, if exercise stress test is used as a standard, the sensitivity of the epinephrine infusion test is 28% and specificity is 98%. Conclusions: Intravenous epinephrine infusion has low sensitivity and may not be considered as an alternative method for a maximal exercise stress test in diagnosis of CPVT. (J Cardiovasc Electrophysiol, Vol. 23, pp. 194‐199, February 2012)     

儿茶酚胺敏感性多形性室性心动过速基因特异性管理

儿茶酚胺敏感性多形性室性心动过速(catecholaminergic polymorphic ventricular tachycardia，CPVT)是一种罕见的遗传性疾病，与基因突变导致的心肌细胞内钙稳态的失衡有关，运动或情绪激动可诱发致命性的室性心律失常。CPVT的诊断基于肾上腺素引起的双向性或多形性室性心动过速，部分患者通过基因检测确诊。在治疗上可通过内、外科方法，抑制或阻断肾上腺素对心肌钙稳态的影响。未正规治疗的患者死亡率高，且猝死常为首发症状。文章阐述CPVT的遗传学新发现及其对临床管理的影响，同时阐述基因检测的局限性和级联筛查的最佳应用。     

Molecular mechanisms of inherited ventricular arrhythmias

BACKGROUND: Inherited ventricular arrhythmias such as the long QT syndrome (LQTS), Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia (CPVT), idiopathic ventricular fibrillation (VF), and arrhythmogenic right ventricular cardiomyopathy (ARVC) account for a relevant proportion of sudden cardiac death cases in young patients cohorts. The detailed pathogenetic mechanisms of inherited ventricular arrhythmias are still poorly understood because systematic investigations are difficult to perform due to low patient numbers and the lack of appropriate experimental models. However, recent advances in research and science have identified a genetic background for many of these diseases. PRESENT KNOWLEDGE: In LQTS, various mutations in different genes encoding for cardiac potassium and sodium channel proteins have been identified ("channelopathy"), and initial progress in genotype-phenotype correlation is made. Mutations in the cardiac sodium channel gene have also been identified in a subset of patients with Brugada syndrome, whereas a genetic background has not yet been demonstrated in idiopathic VF and right ventricular outflow-tract tachycardia (RVO-VT). Very recently, mutations in the cardiac ryanodine receptor gene have been identified in CPVT and in a subgroup of patients with ARVC. Although several chromosomal loci were suggested, no other responsible genes or mutations have been found in autosomal dominant forms of ARVC. However, in Naxos disease, a recessive form of ARVC with coexpression of palmoplantar keratoderma and woolly hair, a mutation in the plakoglobin gene has recently been discovered, thus underscoring the potential role of genetic alterations in cytoskeletal proteins in ARVC. FUTURE PERSPECTIVES: In the next years, significant progress in the genetic diagnosis pathophysiologic understanding of disease mechanisms, genotype-phenotype correlation, and the development of gene- or target-directed treatment strategies can be expected in the field of inherited ventricular arrhythmias. CONCLUSION: This review summarizes the current knowledge of the molecular mechanisms, including aspects of pathoanatomy, autonomic innervation, genetics, and genotype-phenotype correlations with their potential implications for diagnosis and treatment of inherited ventricular arrhythmias.     

Ryanodine receptor and calsequestrin in arrhythmogenesis: What we have learnt from genetic diseases and transgenic mice

The year 2001 has been pivotal for the identification of the molecular bases of catecholaminergic polymorphic ventricular tachycardia (CPVT): a life-threatening genetic disease that predisposes young individuals with normal cardiac structure to cardiac arrest. Interestingly CPVT has been linked to mutations in genes encoding the cardiac ryanodine receptor (RyR2) and cardiac calsequestrin (CASQ2): two fundamental proteins involved in regulation of intracellular Ca²⁺ in cardiac myocytes. The critical role of the two proteins in the heart has attracted interests of the scientific community so that networks of investigators have embarked in translational studies to characterize in vitro and in vivo the mutant proteins. Overall in the last seven years the field has substantially advanced but considerable controversies still exist on the consequences of RyR2 and CASQ2 mutations and on the modalities by which they precipitate cardiac arrhythmias. With so many questions that need to be elucidated it is expected that in the near future the field will remain innovative and stimulating. In this review we will outline how research has advanced in the understanding of CPVT and we will present how the observations made have disclosed novel arrhythmogenic cascades that are likely to impact acquired heart diseases.     

Cardiac Calsequestrin: The New Kid on the Block in Arrhythmias

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare inherited disease characterized by physical or emotional stress-induced ventricular arrhythmias in the absence of any structural heart disease or QT prolongation. Thus far, mutations in genes encoding the sarcoplasmic reticulum Ca²⁺ release channel (RYR2) and the sarcoplasmic reticulum Ca²⁺ binding protein cardiac calsequestrin (CASQ2) have been identified in CPVT patients. Here, we review the role of cardiac calsequestrin in health and disease, with a particular focus on how calsequestrin deficiency can cause arrhythmia susceptibility. Clinical implications and a promising new drug therapy for CPVT are discussed.     

Inherited dysfunction of sarcoplasmic reticulum Ca2+ handling and arrhythmogenesis

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disease occurring in patients with a structurally normal heart: the disease is characterized by life-threatening arrhythmias elicited by stress and emotion. In 2001, the ryanodine receptor was identified as the gene that is linked to CPVT; shortly thereafter, cardiac calsequestrin was implicated in the recessive form of the same disease. It became clear that abnormalities in intracellular Ca(2+) regulation could profoundly disrupt the electrophysiological properties of the heart. In this article, we discuss the molecular basis of the disease and the pathophysiological mechanisms that are impacting clinical diagnosis and management of affected individuals. As of today, the interaction between basic scientists and clinicians to understand CPVT and identify new therapeutic strategies is one of the most compelling examples of the importance of translational research in cardiology.     

A novel early onset lethal form of catecholaminergic polymorphic ventricular tachycardia maps to chromosome 7p14-p22

Introduction: Previously, autosomal dominant catecholaminergic polymorphic ventricular tachycardia (CPVT [1]) was mapped to chromosome 1q42–43 with identification of pathogenic mutations in RYR2. Autosomal recessive CPVT (2) was mapped to chromosome 1p13–21, leading to the identification of mutations in CASQ2. In this study, we aimed to elucidate clinical phenotypes of a new variant of CPVT (3) in an inbred Arab family and also delineate the chromosomal location of the gene causing CPVT (3).
Methods and Results: In a highly inbred family, clinical symptoms of CPVT appeared early in childhood (7–12 years) and in three of the four cases, the first appearance of symptoms turned into a fatal outcome. Parents of the affected children were first-degree cousins and without any symptoms. Segregation analysis suggested an autosomal recessive inheritance. A genome-wide search using polymorphic DNA markers mapped the disease locus to a 25-Mb interval on chromosome 7p14-p22. A maximal multipoint LOD score of 3.17 was obtained at marker D7S493. Sequencing of putative candidate genes, SP4 , NPY , FKBP9 , FKBP14 , PDE1C , and TBX20 , in and around this locus, did not reveal any mutation.
Conclusions: We have identified a novel highly malignant autosomal recessive form of CPVT and mapped this disorder to a 25-Mb interval on chromosome 7p14-p22.     

Unusual clinical presentation in a family with catecholaminergic polymorphic ventricular tachycardia due to a G14876A ryanodine receptor gene mutation

A family was identified, of whom which 11 members were carriers of the G14876A ryanodine 2 receptor mutation. All but 1 were symptomatic at the time of the study. Exercise testing showed bidirectional or polymorphic arrhythmias in 4 patients, whereas in 5 patients, it showed monomorphic or rare minor polymorphic ventricular arrhythmias. Two young patients died suddenly at rest while asleep. This study demonstrates that arrhythmias occurring during exercise stress testing in patients affected by catecholaminergic polymorphic ventricular tachycardia (CPVT) could be minor even in very symptomatic patients. The diagnosis of CPVT must be considered in these patients with a familial history of typical CPVT.     

儿茶酚胺敏感性多形性室速的基因诊治进展

儿茶酚胺敏感性多形性室速(CPVT)是具有较高猝死风险的罕见单基因遗传病.已知多种CPVT基因突变可通过影响肌浆网钙通道蛋白RyR2的功能,破坏细胞内钙稳态,触发室性心律失常,而依靠腺相关病毒载体(AAVs)及CRISPR/Cas9技术进行基因层面的干预有望为CPVT的治疗提供新思路.本文就其遗传特征及基因干预等领域的研究现状作一总结.     

Mechanism underlying catecholaminergic polymorphic ventricular tachycardia and approaches to therapy

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterized by VT induced by adrenergic stress in the absence of structural heart disease and high incidence of sudden cardiac death. The diagnosis is made based on reproducible ventricular tachyarrhythmias including bidirectional VT and polymorphic VT during exercise testings. Two causative genes of CPVT have been identified: RYR2, encoding the cardiac ryanodine receptor (RyR2) Ca²⁺ release channel, and CASQ2, encoding cardiac calsequestrin. A mutation in RYR2 or CASQ2 is identified in approximately 60% of patients with CPVT. Mutations in these two genes destabilize the RyR2 Ca²⁺ release channel complex in sarcoplasmic reticulum and result in spontaneous Ca²⁺ release through RyR2 channels leading to delayed after depolarization, triggered activity, and bidirectional/polymorphic VT. Implantable cardioverter defibrillators (ICDs) are recommended for prevention of sudden death in patients with CPVT.1. A.E. Epstein, J.P. DiMarco, K.A. Ellenbogen, et al., ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices): developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. Circulation. 2008;117:e350 However, painful shocks can trigger further adrenergic stress and arrhythmias, and deaths have occurred despite appropriate ICD shocks. Treatment with β-adrenergic blockers reduces arrhythmia burden and mortality, but is not completely effective. The beneficial effects of Ca²⁺ channel blocker verapamil in combination with β-blocker have been reported, but the role of verapamil has not been well assessed. Because Ca²⁺ leakage through ryanodine channel is a common mechanism of CPVT, ryanodine channel block may have a therapeutic effect. We discovered that flecainide directly inhibits RyR2 channels and prevent CPVT. Left cardiac sympathetic denervation may be an effective alternative treatment in combination with ICD, especially for patients whose arrhythmias are not controlled by drug therapies.     

Human cardiac ryanodine receptor mutations in ion channel disorders in Japan

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is characterized by adrenergic induced bidirectional or polymorphic ventricular tachycardias. Some of CPVT families were reported to be associated with cardiac ryanodine receptor gene (RyR2) mutations. However, association between RyR2 and other arrhythmogenic disorders is not clarified. In this study, we analyzed 83 Japanese patients including patients with long-QT syndrome, Brugada syndrome, idiopathic ventricular fibrillation, arrhythmogenic right ventricular cardiomyopathy and CPVT. Genetic screening of RyR2 revealed 3 distinct mutations among 4 families with CPVT (75% of incidence). However, no mutation was found in other groups. This is the first report to demonstrate prevalence of RyR2 mutations in various arrhythmogenic disorders in Japan. RyR2 mutations were detected frequently in CPVT but not in other diseases.     

Disruption of calcium homeostasis and arrhythmogenesis induced by mutations in the cardiac ryanodine receptor and calsequestrin

Development of cardiac arrhythmias in several degenerative cardiac disorders such as heart failure is precipitated by abnormalities in intracellular calcium regulation. Recently, the identification of mutations in proteins responsible for the control of intracellular calcium has been associated with an inherited arrhythmogenic syndrome called catecholaminergic polymorphic ventricular tachycardia (CPVT). Here, we review the current knowledge about the molecular pathophysiology of CPVT and we discuss some potentially innovative strategies for controlling calcium-handling abnormalities in CPVT that may provide novel therapeutic options for affected patients.     

Catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a highly malignant form of arrhythmogenic disorder characterized by exercise- or emotional-induced polymorphic ventricular tachycardia in the absence of detectable structural heart disease. Because of the typical pattern of arrhythmias (bidirectional ventricular tachycardia and the occurrence and severity of arrhythmia correlated well with exercise workload) during exercise stress test, CPVT can be identified promptly. Molecular genetic screening of the genes encoding the cardiac ryanodine receptor and calsequestrin is critical to confirm uncertain diagnosis of CPVT. With the exception of beta-blockers, no pharmacologic therapy of proven effectiveness is available: although beta-blockers reduce the occurrence of ventricular tachycardia, 30% of patients treated with beta-blockers still experience cardiac arrhythmias and eventually require implantable cardioverter defibrillator implantation to prevent cardiac arrest.