RYR2-ryanodinopathies: from calcium overload to calcium deficiency

Non-juvenile familial form of life-threatening arrhythmias caused by the Ryanodine Receptor type 2 c.13823 G>A, p.(Arg4608Gln) pathogenic variant: Atypical catecholaminergic polymorphic ventricular Tachycardia or misdiagnosis?

BACKGROUND

Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is a rare inherited channelopathy, responsible for potentially lethal malignant arrhythmic episodes. Atypical non-juvenile form of CPVT may not mislead an alternative diagnosis of calcium release deficiency syndrome (CRDS).

CASE

The index case was a 58 years-old woman who experienced aborted sudden cardiac arrest. The initial complete diagnostic workup (including norepinephrine challenge) was completely negative. She was implanted with an entirely subcutaneous defibrillator. During her follow-up, she received an appropriate electrical shock (ventricular fibrillation) despite β-blocker treatment. Three sisters (46, 40 and 18 years-old) as well as 2 cousins, one paternal uncle and one paternal aunt had sudden cardiac deaths (SCD) without etiology in the family history. There were no additional reports of pregnancy loss, neonatal death, seizures or SCD among the family members. The genetic analysis in this proband revealed a missense pathogenic variant c.13823 G>A, p.(Arg4608Gln) in the RYR2 gene, encoding the Ryanodine Receptor type 2. This c.13823 G>A, p.(Arg4608Gln), variant in the RYR2 gene was supposed to be a potential disease-causing variant in CPVT. Unfortunately, before the end of the proband's genetic analysis, her 20 years-old daughter experienced SCD, whilst being implanted with an insertable cardiac monitor. Familial segregation analysis confirmed the four symptomatic sisters harbor also the same variant confirming the pathogenic role of this variant. We also identified 7 carriers who were clinically negative for CPVT in the next generation. Whole were treated with Nadolol 80 mg per day, and the follow-up was uneventful after twenty-four months.

CONCLUSION

The Ryanodine Receptor type 2 c.13823 G>A, p.(Arg4608Gln) pathogenic variant is described in a malignant familial form of CRDS.

Protective role of triiodothyronine in sepsis‑induced cardiomyopathy through phospholamban downregulation

Sepsis is often a cause of mortality in patients admitted to the intensive care unit. Notably, the heart is the organ most susceptible to the impact of sepsis and this condition is referred to as sepsis‑induced cardiomyopathy (SIC). Low triiodothyronine (T3) syndrome frequently occurs in patients with sepsis, and the heart is one of the most important target organs for the action of T3. Phospholamban (PLN) is a key protein associated with Ca2+‑pump‑mediated cardiac diastolic function in the myocardium of mice with SIC, and PLN is negatively regulated by T3. The present study aimed to explore whether T3 can protect cardiac function during sepsis and to investigate the specific molecular mechanism underlying the regulation of PLN by T3. C57BL/6J mice and H9C2 cells were used to establish in vivo and in vitro models, respectively. Myocardial damage was detected via pathological tissue sections, a Cell Counting Kit-8 assay, an apoptosis assay and crystal violet staining. Intracellular calcium levels and reactive oxygen species were detected by Fluo‑4AM and DHE fluorescence. The protein and mRNA expression levels of JNK and c‑Jun were measured by western blotting and reverse transcription‑quantitative PCR to investigate the molecular mechanisms involved. Subsequently, 100 clinical patients were recruited to verify the clinical application value of PLN in SIC. The results revealed a significant negative correlation between PLN and T3 in the animal disease model. Furthermore, the expression levels of genes and proteins in the JNK/c‑Jun signaling pathway and PLN expression levels were decreased, whereas the expression levels of sarcoplasmic reticulum calcium ATPase were increased after T3 treatment. These results indicated that T3 alleviated myocardial injury in SIC by inhibiting PLN expression and its phosphorylation, which may be related to the JNK/c‑Jun signaling pathway. Accordingly, PLN may have clinical diagnostic value in patients with SIC.

The Role of RyR2 Mutations in Congenital Heart Diseases: Insights Into Cardiac Electrophysiological Mechanisms

Ryanodine receptor 2 (RyR2) protein, a calcium ion release channel in the sarcoplasmic reticulum (SR) of myocardial cells, plays a crucial role in regulating cardiac systolic and diastolic functions. Mutations in RyR2 and its dysfunction are implicated in various congenital heart diseases (CHDs). Studies have shown that mutations in the RYR2 gene, which encodes the RyR2 protein, are linked to several cardiac arrhythmias, including catecholaminergic polymorphic ventricular tachycardia (CPVT), long QT syndrome (LQTS), calcium release deficiency syndrome (CRDS), and atrial fibrillation (AF). Additionally, RyR2 mutations have been associated with multiple genetic cardiomyopathies, such as left ventricular non-compaction cardiomyopathy (LVNC), arrhythmogenic right ventricular cardiomyopathy (ARVC), hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). Through various cell and animal models, researchers have developed mutant RyR2 models demonstrated that these mutations often lead to calcium dysregulation, typically resulting in either a gain or loss of function. This comprehensive review delves into the current understanding of RyR2 mutations and their impact on cardiac electrophysiology, focusing on the molecular mechanisms linking these mutations to arrhythmias and cardiomyopathies-an essential step in advancing diagnostic and therapeutic strategies.

Synergy of genetics and lipid metabolism driving feed utilization efficiency in chickens

Residual feed intake (RFI) is a key indicator of feed efficiency, critical for enhancing the economic sustainability of poultry production. However, the genetic and metabolic regulatory mechanisms of RFI remain unclear. This study analyzed the genome, liver transcriptome, metabolome, and lipidome of hens with low and high feed efficiency (N = 60) from the previously established RFI divergent broiler lines (F15). Our results revealed pronounced genetic differentiation between low RFI (LRFI) and high RFI (HRFI) lines and identified genomic signatures of selection associated with feed efficiency. Transcriptomic analysis showed differential expression of genes involved in neural regulation and lipid metabolism. Notably, LRFI chickens exhibited reduced hepatic lipid accumulation, which was associated with decreased fatty acid metabolism and increased cholesterol metabolism (P < 0.05). The lipidomic analysis uncovered distinct profiles of glycerophospholipids (e.g., PE-P and PC-O) and sphingolipids (e.g., ceramides), which were more abundant in LRFI chickens (P < 0.05) and strongly correlated with key lipid metabolism processes (P < 0.05). Despite improved feed efficiency, LRFI chickens demonstrated signs of increased oxidative stress. Moreover, integrative analyses revealed that genes such as MGAT5, GABRA4, and LRRC4C, exhibiting strong selection signatures and higher expression in the LRFI line (P < 0.05), were identified as key regulators of lipid metabolism, potentially contributing to the observed differences in feed efficiency. This comprehensive study highlights the synergistic effect of genetics and lipid metabolism in driving feed utilization efficiency in chickens, establishing a scientific foundation for breeding strategies aimed at improving feed efficiency in poultry production.

X-Chromosome-Linked miRNAs Regulate Sex Differences in Cardiac Physiology

BACKGROUND

Males and females exhibit distinct anatomic and functional characteristics of the heart, predisposing them to specific disease states.

METHODS

We identified microRNAs (miRNAs/miR) with sex-differential expression in mouse hearts.

RESULTS

Four conserved miRNAs are present in a single locus on the X-chromosome and are expressed at higher levels in females than males. We show miRNA, miR-871, is responsible for decreased expression of the protein SRL (sarcalumenin) in females. SRL is involved in calcium signaling, and we show it contributes to differences in electrophysiology between males and females. miR-871 overexpression mimics the effects of the cardiac physiology of conditional cardiomyocyte-specific Srl-null mice. Inhibiting miR-871 with an antagomir in females shortened ventricular repolarization. The human orthologue of miR-871, miR-888, coevolved with the SRL 3' untranslated region and regulates human SRL.

CONCLUSIONS

These data highlight the importance of sex-differential miRNA mechanisms in mediating sex-specific functions and their potential relevance to human cardiac diseases.

Ruxolitinib as a CaMKII inhibitor for treatment of cardiac arrhythmias: Applications and prospects

Recent studies have highlighted the critical role of calcium/calmodulin-dependent protein kinase II (CaMKII) overactivation in the pathogenesis of various cardiac arrhythmias. Ruxolitinib, a Janus kinase inhibitor widely used for the treatment of myelofibrosis and acute graft-vs-host disease, has expanded its research horizons to include its potential as a CaMKII inhibitor in the treatment of cardiac arrhythmias. This article reviews the basic pharmacologic properties of ruxolitinib and delves into the role of CaMKII in cardiac arrhythmias, including its structural fundamentals, activation mechanisms, and association with arrhythmic conditions. Furthermore, the current state of CaMKII inhibitor research is discussed, with a special focus on the advances and clinical potential of ruxolitinib in this field. Studies indicate that ruxolitinib effectively inhibits CaMKII activity and has therapeutic potential against cardiac arrhythmias in animal models and at the cellular level. In addition, we address the critical issues that need to be resolved before the clinical application of ruxolitinib in arrhythmia treatment, including dosage concerns, long-term inhibitory effects, potential impacts on the nervous system, and efficacy across different types of arrhythmias. Future research directions involve further exploration of the clinical application potential of ruxolitinib, particularly in diseases such as heart failure, hypertrophic cardiomyopathy, dilated cardiomyopathy, and ischemic arrhythmias. In summary, the efficacy, low toxicity, and safety profile of ruxolitinib as a CaMKII inhibitor in the treatment of cardiac arrhythmias suggest a promising future for its development as a therapeutic drug in this domain.

Flecainide Specifically Targets the Monovalent Countercurrent Through the Cardiac Ryanodine Receptor, While a Dominant Opposing Ca2+/Ba2+ Current Is Present

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a highly arrhythmogenic syndrome triggered by stress, primarily linked to gain-of-function point mutations in the cardiac ryanodine receptor (RyR2). Flecainide, as an effective therapy for CPVT, is a known blocker of the surface-membrane Na+ channel, also affecting the intracellular RyR2 channel. The therapeutic relevance of the flecainide-RyR2 interaction remains controversial, as flecainide blocks only the RyR2 current flowing in the opposite direction to the physiological Ca2+ release from the sarcoplasmic reticulum (SR). However, it has been proposed that charge-compensating countercurrent from the cytosol to SR lumen plays a critical role, and its reduction may indeed suppress excessive diastolic SR Ca2+ release through RyR2 channels in CPVT. Monitoring single-channel properties, we examined whether flecainide can target intracellular pathways for charge-balancing currents carried by RyR2 and SR Cl- channels under cell-like conditions. Particularly, the Tris+ countercurrent flowed through the RyR2 channel simultaneously with a dominant reverse Ca2+/Ba2+ current. We demonstrate that flecainide blocked the RyR2-mediated countercurrent without affecting channel activity. In contrast, the SR Cl- channel was completely resistant to flecainide. Based on these findings, it is reasonable to propose that the primary intracellular target of flecainide in vivo is the RyR2-mediated countercurrent.

Pediatric flecainide pharmacogenomics: a roadmap to delivering precision-based care to pediatrics arrhythmias

Flecainide acetate is a Class 1c anti-arrhythmic with a potent sodium voltage gated channel blockade which is utilized for the second-line treatment of tachyarrhythmias in children and adults. Given its narrow therapeutic index, the individualization of drug therapy is of utmost importance for clinicians. Despite efforts to improve anti-arrhythmic drug therapy, there remain knowledge gaps regarding the impact of variation in the genes relevant to flecainide's disposition and response. This variability is compounded in developing children whose drug disposition and response pathways may remain immature. The purpose of this comprehensive review is to outline flecainide's disposition and response pathways while simultaneously highlighting opportunities for prospective investigation in the pediatric population.

Attempts to Create Transgenic Mice Carrying the Q3924E Mutation in RyR2 Ca2+ Binding Site

Over 200 point mutations in the ryanodine receptor (RyR2) of the cardiac sarcoplasmic reticulum (SR) are known to be associated with cardiac arrhythmia. We have already reported on the calcium signaling phenotype of a point mutation in RyR2 Ca2+ binding site Q3925E expressed in human stem-cell-derived cardiomyocytes (hiPSC-CMs) that was found to be lethal in a 9-year-old girl. CRISPR/Cas9-gene-edited mutant cardiomyocytes carrying the RyR2-Q3925E mutation exhibited a loss of calcium-induced calcium release (CICR) and caffeine-triggered calcium release but continued to beat arrhythmically without generating significant SR Ca2+ release, consistent with a remodeling of the calcium signaling pathway. An RNAseq heat map confirmed significant changes in calcium-associated genes, supporting the possibility of remodeling. To determine the in situ cardiac phenotype in an animal model of this mutation, we generated a knock-in mouse model of RyR2-Q3924E+/- using the CRISPR/Cas9 technique. We obtained three homozygous and one chimera mice, but they all died before reaching 3 weeks of age, preventing the establishment of germline mutation transmission in their offspring. A histo-pathological analysis of the heart showed significant cardiac hypertrophy, suggesting the Q3924E-RyR2 mutation was lethal to the mice.

A case report of familial catecholaminergic polymorphic ventricular tachycardia with a novel mutation in the ryanodine receptor 2

Background

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is suspected by clinical characteristics involving fatal arrhythmic events in childhood and adolescence. On the other hand, genetic testing is also important because the mutation site in the specific genes of CPVT is related to the risk of ventricular arrhythmias and gene penetrance.

Case summary

We present a case of a 15-year-old male with a familial history of CPVT and a history of syncope at the age of 5. He experienced a cardiac arrest prompting out-of-hospital cardiopulmonary resuscitation, and his circulatory dynamics recovered. Multiple premature ventricular contractions inducted by a treadmill exercise test disappeared after a dosage of verapamil, flecainide, and nadolol, and a subcutaneous implantable cardioverter defibrillator was implanted. The novel pathogenic mutation with an insertion of histidine near the C-terminus of the RYR2 protein was identified by genetic testing in this case and his mother.

Discussion

The RYR2 mutation in this case has not been previously reported and may be an intractable phenotype of CPVT associated with a strong familial history and fatal cardiac events even under adequate medical therapy.

The genome landscape of the Xinglong buffalo

BACKGROUND

Xinglong buffalo, as an indigenous breed in Hainan province of China, possesses characteristics such as high humidity tolerance, disease resistance and high reproductive capacity. Combined with whole genome sequencing technology, comprehensive investigation can be undertaken to elucidate the genomic characteristics, functions and genetic variation of Xinglong buffalo population.

RESULTS

Xinglong buffalo has the highest genetic diversity, lowest runs of homozygosity average length, and fasted decay of linkage disequilibrium in our study population. Phylogenetic tree results revealed that Xinglong buffalo was gathered together with Fuzhong buffalo firstly. The population genetic structure analysis indicates that at K = 3, the Xinglong buffalo for the first time showed a distinct ancestral origin from other water buffalo. Furthermore, compared to different populations, candidate genes displaying significantly distinct patterns of single nucleotide polymorphisms (SNPs) (e.g., RYR2, COX15, PCDH9, DTWD2, FCRL5) distribution have been identified in the Xinglong buffalo.

CONCLUSIONS

Based on the whole genome sequencing data, this study identified a substantial number of SNPs and assessed the genetic diversity and selection signatures within the Xinglong buffalo population. These results contribute to understanding the genomic characteristics of Xinglong buffalo and their genetic evolutionary status. However, the practical significance of these signatures for genetic enhancement still requires confirmation through additional samples and further experimental validation.

Assaying sarcoplasmic reticulum Ca2+-leak in mouse atrial myocytes

More and more studies have suggested an essential role of sarcoplasmic reticulum (SR) Ca2+ leak of atrial myocytes in atrial diseases such as atrial fibrillation (AF). The increasing interest in atrial Ca2+ signaling makes it necessary to develop a more accurate approach for Ca2+ measurement in atrial myocytes due to obvious differences between atrial and ventricular Ca2+ handling. In the present study, we proposed a new approach for quantifying total SR Ca2+ leak in atrial myocytes with confocal line-scan Ca2+ images. With a very precious approximation of the histogram of normalized line-scan Ca2+ images by using a modified Gaussian distribution, we separated the signal pixel components from noisy pixels and extracted two new dimensionless parameters, F signals and R signals, to reflect the summation of signal pixels and their release components, respectively. In the presence of tetracaine blocking SR Ca2+ leak, the two parameters were very close to 0, and in atrial myocytes under normal conditions, the two parameters are well positive correlative with Ca2+ spark frequency and total signal mass, the two classic readouts for SR Ca2+ leak. Consistent with Ca2+ Spark readouts, the two parameters quantified a significant increase of SR Ca2+ leak in atrial myocytes from mice harboring a leaky type 2 ryanodine receptor mutation (RyR2-R2474S+/-) compared to the WT group. Collectively, this study proposed a simple and effective approach to quantify SR Ca2+ leak in atrial myocytes, which may benefit research on calcium signaling in atrial physiology and diseases.

Profiling Reduced Expression of Contractile and Mitochondrial mRNAs in the Human Sinoatrial Node vs. Right Atrium and Predicting Their Suppressed Expression by Transcription Factors and/or microRNAs

(1) Background: The sinus node (SN) is the main pacemaker of the heart. It is characterized by pacemaker cells that lack mitochondria and contractile elements. We investigated the possibility that transcription factors (TFs) and microRNAs (miRs) present in the SN can regulate gene expression that affects SN morphology and function. (2) Methods: From human next-generation sequencing data, a list of mRNAs that are expressed at lower levels in the SN compared with the right atrium (RA) was compiled. The mRNAs were then classified into contractile, mitochondrial or glycogen mRNAs using bioinformatic software, RStudio and Ingenuity Pathway Analysis. The mRNAs were combined with TFs and miRs to predict their interactions. (3) Results: From a compilation of the 1357 mRNAs, 280 contractile mRNAs and 198 mitochondrial mRNAs were identified to be expressed at lower levels in the SN compared with RA. TFs and miRs were shown to interact with contractile and mitochondrial function-related mRNAs. (4) Conclusions: In human SN, TFs (MYCN, SOX2, NUPR1 and PRDM16) mainly regulate mitochondrial mRNAs (COX5A, SLC25A11 and NDUFA8), while miRs (miR-153-3p, miR-654-5p, miR-10a-5p and miR-215-5p) mainly regulate contractile mRNAs (RYR2, CAMK2A and PRKAR1A). TF and miR-mRNA interactions provide a further understanding of the complex molecular makeup of the SN and potential therapeutic targets for cardiovascular treatments.

Minocycline Inhibits Tick-Borne Encephalitis Virus and Protects Infected Cells via Multiple Pathways

Tick-borne Encephalitis (TBE) is a zoonotic disease caused by the Tick-borne Encephalitis virus (TBEV), which affects the central nervous system of both humans and animals. Currently, there is no specific therapy for patients with TBE, with symptomatic treatment being the primary approach. In this study, the effects of minocycline (MIN), which is a kind of tetracycline antibiotic, on TBEV propagation and cellular protection in TBEV-infected cell lines were evaluated. Indirect immunofluorescence, virus titers, and RT-qPCR results showed that 48 h post-treatment with MIN, TBEV replication was significantly inhibited in a dose-dependent manner. In addition, the inhibitory effect of MIN on different TBEV multiplicities of infection (MOIs) in Vero cells was studied. Furthermore, the transcriptomic analysis and RT-qPCR results indicate that after incubation with MIN, the levels of TBEV and CALML4 were decreased, whereas the levels of calcium channel receptors, such as RYR2 and SNAP25, were significantly increased. MIN also regulated MAPK-ERK-related factors, including FGF2, PDGFRA, PLCB2, and p-ERK, and inhibited inflammatory responses. These data indicate that administering MIN to TBEV-infected cells can reduce the TBEV level, regulate calcium signaling pathway-associated proteins, and inhibit the MAPK-ERK signaling pathway and inflammatory responses. This research offers innovative strategies for the advancement of anti-TBEV therapy.

Clinical characteristics and follow-up of complex arrhythmias associated with RYR2 gene mutations in children

Objective

The aim of this study was to analyze the diagnosis, treatment, and follow-up of six cases of complex arrhythmias associated with RYR2 gene mutations in children.

Method

A retrospective analysis was conducted on six children diagnosed with complex arrhythmias associated with RYR2 gene mutations. The study included an analysis of the age of onset, initial symptoms, electrocardiographic characteristics, genetic results, treatment course, and follow-up outcomes.

Results

Among the six cases included in the study, there were four males and two females, with an average age of 3.5 ± 0.5 years. The average time from initial symptoms to diagnosis was 2.7 ± 1.3 years. The most common clinical manifestation was syncope, with exercise and emotions being the main triggers. All six children had de novo missense mutations in the RYR2 gene identified through whole-exome sequencing. In Holter electrocardiogram, atrial arrhythmias and sinoatrial node dysfunction were commonly observed in younger children. Four patients underwent exercise stress testing, with two experiencing bidirectional ventricular premature contractions and two experiencing bidirectional ventricular tachycardia and polymorphic ventricular tachycardia. Initial treatment involved oral propranolol or metoprolol. If arrhythmias persisted, flecainide or propafenone was added as adjunctive therapy. Two patients received permanent cardiac pacemaker treatment (single chamber ventricular pacemaker, VVI). All patients survived, with three experiencing occasional syncope during treatment. The follow-up period ranged from 12 to 37 months, with an average follow-up time of 24.3 ± 3.7 months.

Conclusion

Complex arrhythmias associated with RYR2 gene mutations in children can present with various clinical manifestations. Atrial arrhythmias combined with sinoatrial node dysfunction are commonly observed in younger children, and the combination of pharmacological therapy and cardiac pacemaker treatment yields favourable treatment outcomes.

Ventricular Tachycardia Due to Triggered Activity: Role of Early and Delayed Afterdepolarizations

Most forms of sustained ventricular tachycardia (VT) are caused by re-entry, resulting from altered myocardial conduction and refractoriness secondary to underlying structural heart disease. In contrast, VT caused by triggered activity (TA) is unrelated to an abnormal structural substrate and is often caused by molecular defects affecting ion channel function or regulation of intracellular calcium cycling. This review summarizes the cellular and molecular bases underlying TA and exemplifies their clinical relevance with selective representative scenarios. The underlying basis of TA caused by delayed afterdepolarizations is related to sarcoplasmic reticulum calcium overload, calcium waves, and diastolic sarcoplasmic reticulum calcium leak. Clinical examples of TA caused by delayed afterdepolarizations include sustained right and left ventricular outflow tract tachycardia and catecholaminergic polymorphic VT. The other form of afterpotentials, early afterdepolarizations, are systolic events and inscribe early afterdepolarizations during phase 2 or phase 3 of the action potential. The fundamental defect is a decrease in repolarization reserve with associated increases in late plateau inward currents. Malignant ventricular arrhythmias in the long QT syndromes are initiated by early afterdepolarization-mediated TA. An understanding of the molecular and cellular bases of these arrhythmias has resulted in generally effective pharmacologic-based therapies, but these are nonspecific agents that have off-target effects. Therapeutic efficacy may need to be augmented with an implantable defibrillator. Next-generation therapies will include novel agents that rescue arrhythmogenic abnormalities in cellular signaling pathways and gene therapy approaches that transfer or edit pathogenic gene variants or silence mutant messenger ribonucleic acid.

Human Genetics of Cardiac Arrhythmias

Inherited forms of cardiac arrhythmias mostly are rare diseases (prevalence <1:2000) and considered to be either "primary electrical heart disorders" due to the absence of structural heart abnormalities or "cardiac ion channel disorders" due to the myocellular structures involved. Precise knowledge of the electrocardiographic features of these diseases and their genetic classification will enable early disease recognition and prevention of cardiac events including sudden cardiac death.The genetic background of these diseases is complex and heterogeneous. In addition to the predominant "private character" of a mutation in each family, locus heterogeneity involving many ion channel genes for the same familial arrhythmia syndrome is typical. Founder pathogenic variants or mutational hot spots are uncommon. Moreover, phenotypes may vary and overlap even within the same family and mutation carriers. For the majority of arrhythmias, the clinical phenotype of an ion channel mutation is restricted to cardiac tissue, and therefore, the disease is nonsyndromic.Recent and innovative methods of parallel DNA analysis (so-called next-generation sequencing, NGS) will enhance further mutation and other variant detection as well as arrhythmia gene identification.

Assessment of Sudden Cardiac Death Risk in Pediatric Primary Electrical Disorders: A Comprehensive Overview

Sudden cardiac death (SCD) in children is a devastating event, often linked to primary electrical diseases (PED) of the heart. PEDs, often referred to as channelopathies, are a group of genetic disorders that disrupt the normal ion channel function in cardiac cells, leading to arrhythmias and sudden cardiac death. This paper investigates the unique challenges of risk assessment and stratification for channelopathy-related SCD in pediatric patients-Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, idiopathic ventricular fibrillation, long QT syndrome, Anderson-Tawil syndrome, short QT syndrome, and early repolarization syndrome. We explore the intricate interplay of genetic, clinical, and electrophysiological factors that contribute to the complex nature of these conditions. Recognizing the significance of early identification and tailored management, this paper underscores the need for a comprehensive risk stratification approach specifically designed for pediatric populations. By integrating genetic testing, family history, and advanced electrophysiological evaluation, clinicians can enhance their ability to identify children at the highest risk for SCD, ultimately paving the way for more effective preventive strategies and improved outcomes in this vulnerable patient group.

Construction of a risk scoring system using clinical factors and RYR2 polymorphisms for bleeding complications in patients on direct oral anticoagulants

Introduction: Bleeding is one of the most undesirable complications of direct oral anticoagulants (DOACs). While the ryanodine receptor (RYR2) has been related to cardiac diseases, research on bleeding complications is lacking. This study aimed to elucidate the association between RYR2 and bleeding risk to develop the risk scoring system in patients treated with DOACs. Methods: This study was a retrospective analysis of prospectively collected samples. We selected ten SNPs within the RYR2 gene, and two models were constructed (Model I: demographic factors only, Model II: demographic and genetic factors) in multivariable analysis. Independent risk factors for bleeding were used to develop a risk scoring system. Results: A total of 447 patients were included, and 49 experienced either major bleeding or clinically relevant non-major bleeding. In Model I, patients using rivaroxaban and experiencing anemia exhibited an increased bleeding risk after adjusting for covariates. Upon incorporating genetic factors into Model I, a significant association with bleeding was also observed in cases of overdosing on DOACs and in patients with a creatinine clearance (CrCl) < 30 mL/min, in addition to rivaroxaban and anemia (Model II). Among genetic factors, RYR2 rs12594 GG, rs17682073 AA, rs3766871 GG, and rs6678625 T alleles were associated with bleeding complications. The area under the receiver operating characteristic curve (AUROC) of Model I was 0.670, whereas that of Model II increased to 0.803, demonstrating better performance with the inclusion of genetic factors. Using the significant variables in Model II, a risk scoring system was constructed. The predicted bleeding risks for scores of 0, 1-2, 3-4, 5-6, 7-8, and 9-10 points were 0%, 1.2%, 4.6%, 15.7%, 41.7%, and 73.3%, respectively. Conclusion: This study revealed an association between RYR2 and bleeding complications among patients taking DOACs and established a risk scoring system to support individualized DOAC treatment for these patients.

Calcium Signaling Consequences of RyR2-S4938F Mutation Expressed in Human iPSC-Derived Cardiomyocytes

Type-2 ryanodine receptor (RyR2) is the major Ca2+ release channel of the cardiac sarcoplasmic reticulum (SR) that controls the rhythm and strength of the heartbeat, but its malfunction may generate severe arrhythmia leading to sudden cardiac death or heart failure. S4938F-RyR2 mutation in the carboxyl-terminal was expressed in human induced pluripotent stem cells derived cardiomyocytes (hiPSC-CMs) using CRISPR/Cas9 gene-editing technique. Ca2+ signaling and electrophysiological properties of beating cardiomyocytes carrying the mutation were studied using total internal reflection fluorescence microscopy (TIRF) and patch clamp technique. In mutant cells, L-type Ca2+ currents (ICa), measured either by depolarizations to zero mV or repolarizations from +100 mV to -50 mV, and their activated Ca2+ transients were significantly smaller, despite their larger caffeine-triggered Ca2+ release signals compared to wild type (WT) cells, suggesting ICa-induced Ca2+ release (CICR) was compromised. The larger SR Ca2+ content of S4938F-RyR2 cells may underlie the higher frequency of spontaneously occurring Ca2+ sparks and Ca2+ transients and their arrhythmogenic phenotype.