A novel RyR2 mutation associated with co-morbid catecholaminergic polymorphic ventricular tachycardia (CPVT) and benign epilepsy with centrotemporal spikes (BECTS)

In this case report, we describe a 14-year-old patient with a novel RyR2 gene mutation (c.6577G > T/p.Val2193Leu), identified through a comprehensive review of medical history, examination findings, and follow-up data. The pathogenic potential of this mutation, which results in the loss of some interatomic forces and compromises the closure of the RyR2 protein pore leading to calcium leakage, was analyzed using the I-TASSER Suite to predict the structural changes in the protein. This mutation manifested clinically as co-morbid catecholaminergic polymorphic ventricular tachycardia (CPVT) and benign epilepsy with centrotemporal spikes (BECTS), a combination not previously documented in the same patient. While seizures were successfully managed with levetiracetam, the patient's exercise-induced syncope episodes could not be controlled with metoprolol, highlighting the complexity and challenge in managing CPVT associated with this novel RyR2 variation.

Dual effect of cardiac FKBP12.6 overexpression on excitation-contraction coupling and the incidence of ventricular arrhythmia depending on its expression level

FKBP12.6, a binding protein to the immunosuppressant FK506, which also binds the ryanodine receptor (RyR2) in the heart, has been proposed to regulate RyR2 function and to have antiarrhythmic properties. However, the level of FKBP12.6 expression in normal hearts remains elusive and some controversies still persist regarding its effects, both in basal conditions and during β-adrenergic stimulation. We quantified FKBP12.6 in the left ventricles (LV) of WT (wild-type) mice and in two novel transgenic models expressing distinct levels of FKBP12.6, using a custom-made specific anti-FKBP12.6 antibody and a recombinant protein. FKBP12.6 level in WT LV was very low (0.16 ± 0.02 nmol/g of LV), indicating that <15% RyR2 monomers are bound to the protein. Mice with 14.1 ± 0.2 nmol of FKBP12.6 per g of LV (TG1) had mild cardiac hypertrophy and normal function and were protected against epinephrine/caffeine-evoked arrhythmias. The ventricular myocytes showed higher [Ca2+]i transient amplitudes than WT myocytes and normal SR-Ca2+ load, while fewer myocytes showed Ca2+ sparks. TG1 cardiomyocytes responded to 50 nM Isoproterenol increasing these [Ca2+]i parameters and producing RyR2-Ser2808 phosphorylation. Mice with more than twice the TG1 FKBP12.6 value (TG2) showed marked cardiac hypertrophy with calcineurin activation and more arrhythmias than WT mice during β-adrenergic stimulation, challenging the protective potential of high FKBP12.6. RyR2R420Q CPVT mice overexpressing FKBP12.6 showed fewer proarrhythmic events and decreased incidence and duration of stress-induced bidirectional ventricular tachycardia. Our study, therefore, quantifies for the first time endogenous FKBP12.6 in the mouse heart, questioning its physiological relevance, at least at rest due its low level. By contrast, our work demonstrates that with caution FKBP12.6 remains an interesting target for the development of new antiarrhythmic therapies.

Generation of two induced pluripotent stem cell lines from catecholaminergic polymorphic ventricular tachycardia patients carrying RYR2 mutations

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a congenital arrhythmic syndrome caused by the RYR2 gene encoded ryanodine receptor. Mutations on RYR2 are commonly associated with ventricular tachycardia after adrenergic stimulation, leading to lethal arrhythmias and sudden cardiac death. We generated two human induced pluripotent stem cell (iPSC) lines from CPVT affected patients carrying single missense heterozygote RYR2 mutations, c.1082 G > A and c.100 A > C. Pluripotency and differentiation capability into derivatives of three germ layers were evaluated along with karyotype stability in the report. The generated patient-specific iPSC lines provide a reliable tool to investigate the CPVT phenotype and understand underlaying mechanisms.

SIDS associated RYR2 p.Arg2267His variant may lack pathogenicity

Sudden infant death syndrome (SIDS) is the sudden death of an infant under 1 year of age that remains unexplained after death scene and medicolegal investigation, including a complete autopsy and clinical history review. The fatal event typically occurs during sleep and heart rhythm during the event is rarely documented. Large series which have utilized molecular autopsy show that long QT syndrome (LQTS) associated cardiac channel mutations contribute to between 5 and 10% of SIDS deaths. In addition, rare novel RYR2 variants have been identified in SIDS victims. Given the lack of a phenotype, the pathogenicity of these variants is inferred from in vitro studies. We report a family with 5 members (mother and 4 children) who are carriers of a rare RYR2 variant (c.6800G > A, p.Arg2267His [Exon: 45], heterozygous) which has previously been identified in a SIDS victim and shown to confer a gain-of-function CPVT phenotype in vitro. All of these 5 family members including the mother (age range 7 to 41 years) have had negative exercise stress tests, echocardiograms and Holter monitors. These findings suggest that caution should be exercised in inferring pathogenicity of rare RYR2 variants based on in vitro functional data which does not always translate to human phenotype.

Clinical and genetic investigation of catecholaminergic polymorphic ventricular tachycardia in a consanguineous Tunisian family

Background: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare disease presenting with syncopal events and sudden cardiac death at a young age in the absence of structural heart disease. Two major genes have been shown to be responsible for CPVT: RYR2 and CASQ2 genes involved in calcium homeostasis. Methods: We report here clinical and molecular investigation of a consanguineous Tunisian family including three affected members. Involvement of RYR2 and CASQ2 genes was investigated. Results: Mutation screening for RYR2 gene showed that no mutation were detected in the coding sequence. A novel variation c.572C/T was identified in CASQ2 gene leading to a p.Pro191Leu. Conclusion: To our knowledge, this is the first clinical and genetic investigation of CPVT in North Africa.

A compound heterozygosity of Tecrl gene confirmed in a catecholaminergic polymorphic ventricular tachycardia family

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is one of the most common causes of sudden cardiac death (SCD) during childhood and in adolescence. Trans-2, 3-enoyl-CoA reductase-like (Tecrl) gene mutations (Arg196Gln and c.331+1G > A splice site mutation) were first reported in CPVT. Tecrl homozygous c.331+1G > A splice site mutation in iPSCs revealed a definite correlation between Tecrl and Ca²⁺ transport in cardiomyocytes. However, no other researchers have confirmed Tecrl mutations in CPVT with literature review. In this study, a case of compound heterozygosity in the Tecrl gene (Arg196Gln and c.918+3T > G splice site mutation) was first identified in a 13-year-old boy with CPVT by whole-exome sequencing (WES) and confirmed by Sanger sequence. Support vector machine and neural network analysis predicted that Arg196Gln mutation could decrease the stability of Tecrl structure, the confidence scores were -0.8929 and -0.9930. A STRUM server also confirmed that Arg196Gln mutation may decrease the binding capacity of the substrate and cause an amino acid substitution immediately upstream of the 3-oxo-5-alpha steroid 4-dehydrogenase domain. According to the "human splicing finder" indication and Alamut Visual Splicing Prediction, the c.918 + 3T > G mutation could influence Tecrl variable splicing. Thus, we confirmed that Tecrl as a new gene which is associated with CPVT.

Calcium signaling in human stem cell-derived cardiomyocytes: Evidence from normal subjects and CPVT afflicted patients

Derivation of cardiomyocyte cell lines from human fibroblasts (induced pluripotent stem cells, iPSCs) has made it possible not only to investigate the electrophysiological and Ca(2+) signaling properties of these cells, but also to determine the altered electrophysiological and Ca(2+)-signaling profiles of such cells lines derived from patients expressing mutation-inducing pathologies. This approach has the potential of generating in vitro human models of cardiovascular diseases where cellular pathology can be investigated in detail and possibly specific pharmacotherapy developed. Although this approach has been applied to a number of mutations in channel proteins that cause arrhythmias, there are only few detailed reports addressing Ca(2+) signaling pathologies beyond measurements of Ca(2+) transients in intact non-voltage clamped cells. Unfortunately, full understanding of Ca(2+) signaling pathologies remains elusive, not only because of the plethora of Ca(2+) signaling proteins defects that cause arrhythmias and cardiomyopathies, but also because detailed functional properties of Ca(2+) signaling proteins are difficult to obtain. Catecholaminergic polymorphic ventricular tachycardia (CPVT1) is a malignant inherited arrhythmogenic disorder predominantly caused by mutations in the cardiac ryanodine receptor (RyR2). Thus far over 150 mutations in RyR2 have been identified that appear to cause this arrhythmia, a number of which have been expressed and studied in transgenic mice or cell-line models. The development of human iPSC-technology makes it possible to create human heart cell-lines carrying these mutations, making detailed identification of Ca(2+) signaling defects and its specific pharmacotherapy possible. In this review we shall first briefly summarize the essential characteristics of the mammalian cardiac Ca(2+) signaling, then compare them to Ca(2+) signaling phenotypes of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) and to those of rat neonatal cardiomyocytes, and categorize the possible variance in Ca(2+) signaling defects caused by different CPVT-inducing mutations as expressed in hiPSC-CMs.

Current topics in catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is induced by emotions or exercise in patients without organic heart disease and may be polymorphic or bidirectional in nature. The prognosis of CPVT is not good, and therefore prevention of sudden death is of utmost importance. Genetic variants of CPVT include RyR2, CASQ2, CALM2, TRD, and possibly KCNJ2 and ANK2 gene mutations. Hypotheses that suggest the causes of CPVT include weakened binding of FKBP12.6 and RyR2, a store overload-induced Ca²⁺ release (SOICR), unzipping of intramolecular domain interactions in RyR2, and molecular and functional abnormalities caused by mutations in the CASQ2 gene. The incidence of an RyR2 anomaly in CPVTs is about 35-79%, whereas anomalies in the CASQ2 gene account for 3-5% CPVTs. The ping-pong theory, suggesting that reciprocating delayed after depolarization induces bigeminy of the right and left bundle branches, may explain the pathogenesis of bidirectional ventricular tachycardia. Flecainide, carvedilol, left sympathetic nerve denervation, and catheter ablation of the PVC may serve as new therapeutic strategies for CPVT while gene-therapy may be applied to some types of CPVT in the future. Although, not all sudden cardiac deaths in CPVT patients are currently preventable, new medical and interventional therapies may improve CPVT prognosis.

Effective cascade screening through identification of a mutation in RYR2 in a large family with a history of sudden death

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disorder which usually presents in the first or second decade of life with syncope, which is typically induced by emotional stress or exercise. We describe a large family with a history of three sudden unexpected deaths. Investigations in the sibling of a deceased individual affected by emotion-induced syncope revealed ventricular bigeminy. Molecular genetic testing was performed on one symptomatic individual and a missense mutation in RYR2 was identified consistent with a diagnosis of CPVT. Subsequent cascade testing of family members excluded 37 of 43 individuals from risk and facilitated preventative intervention. This case highlights the value of genotyping in sudden cardiac death by defining the precise diagnosis and through the identification and exclusion of at-risk individuals. <Learning objective: The diagnosis of CPVT should be considered in families with a history of sudden death in a previously asymptomatic young person. Cascade molecular genetic testing should be undertaken as, if a pathogenic mutation is found, this can distinguish it from other arrhythmogenic disorders and can identify at-risk individuals allowing treatment to be targeted at those in need, thus helping to reduce the mortality associated with the condition.>.