Loss-of-function mutations in the cardiac calcium channel underlie a new clinical entity characterized by ST-segment elevation, short QT intervals, and sudden cardiac death

Congenital short QT syndrome: A review focused on electrocardiographic features

Congenital short QT syndrome is a very low prevalence inherited primary arrhythmia syndrome first reported in 2000 by Gussak et al., who described two families with a short QT interval, syncope, and sudden cardiac death. In 2004, Ramon Brugada et al. identified the first genetic type of this entity. To date, a total of nine genotypes have been described. The diagnosis is easy from the electrocardiogram (ECG), not only due to the short QT duration, but also based on other aspects covered in this review. During 24-h Holter monitoring, paroxysmal atrial fibrillation spontaneously converting to sinus rhythm may be found. Even though the T wave may appear symmetric on the ECG, the T loop of the vectorcardiogram confirms that the T wave is constantly asymmetric due to the presence of dashes closer to each other in the efferent branch. In this review, we also describe the minus-plus T wave sign that we have described in a previously published article. In addition to congenital causes, we briefly highlight the existence of numerous acquired causes of short QT interval.

Bipolar Patient-Specific In Vitro Diagnostic Test Reveals Underlying Cardiac Arrhythmia Phenotype Caused by Calcium Channel Genetic Risk Factor

A common genetic risk factor for bipolar disorder is CACNA1C, a gene that is also critical for cardiac rhythm. The impact of CACNA1C mutations on bipolar patient cardiac rhythm is unknown. Here, we report the cardiac electrophysiological implications of a bipolar disorder-associated genetic risk factor in CACNA1C using patient induced pluripotent stem cell-derived cardiomyocytes. Results indicate that the CACNA1C bipolar disorder-related mutation causes cardiac electrical impulse conduction slowing mediated by impaired intercellular coupling via connexin 43 gap junctions. In vitro gene therapy to restore connexin 43 expression increased cardiac electrical impulse conduction velocity and protected against thioridazine-induced QT prolongation. Patients positive for bipolar disorder CACNA1C genetic risk factors may have elevated proarrhythmic risk for adverse events in response to psychiatric medications that slow conduction or prolong the QT interval. This in vitro diagnostic tool enables cardiac testing specific to patients with psychiatric disorders to determine their sensitivity to off-target effects of psychiatric medications.

Impacts of gene variants on drug effects-the foundation of genotype-guided pharmacologic therapy for long QT syndrome and short QT syndrome

The clinical significance of optimal pharmacotherapy for inherited arrhythmias such as short QT syndrome (SQTS) and long QT syndrome (LQTS) has been increasingly recognised. The advancement of gene technology has opened up new possibilities for identifying genetic variations and investigating the pathophysiological roles and mechanisms of genetic arrhythmias. Numerous variants in various genes have been proven to be causative in genetic arrhythmias. Studies have demonstrated that the effectiveness of certain drugs is specific to the patient or genotype, indicating the important role of gene-variants in drug response. This review aims to summarize the reported data on the impact of different gene-variants on drug response in SQTS and LQTS, as well as discuss the potential mechanisms by which gene-variants alter drug response. These findings may provide valuable information for future studies on the influence of gene variants on drug efficacy and the development of genotype-guided or precision treatment for these diseases.

Management of patients with an electrical storm or clustered ventricular arrhythmias: a clinical consensus statement of the European Heart Rhythm Association of the ESC-endorsed by the Asia-Pacific Heart Rhythm Society, Heart Rhythm Society, and Latin-American Heart Rhythm Society

Electrical storm (ES) is a state of electrical instability, manifesting as recurrent ventricular arrhythmias (VAs) over a short period of time (three or more episodes of sustained VA within 24 h, separated by at least 5 min, requiring termination by an intervention). The clinical presentation can vary, but ES is usually a cardiac emergency. Electrical storm mainly affects patients with structural or primary electrical heart disease, often with an implantable cardioverter-defibrillator (ICD). Management of ES requires a multi-faceted approach and the involvement of multi-disciplinary teams, but despite advanced treatment and often invasive procedures, it is associated with high morbidity and mortality. With an ageing population, longer survival of heart failure patients, and an increasing number of patients with ICD, the incidence of ES is expected to increase. This European Heart Rhythm Association clinical consensus statement focuses on pathophysiology, clinical presentation, diagnostic evaluation, and acute and long-term management of patients presenting with ES or clustered VA.

MATR3 pathogenic variants differentially impair its cryptic splicing repression function

Matrin-3 (MATR3) is an RNA-binding protein implicated in neurodegenerative and neurodevelopmental diseases. However, little is known regarding the role of MATR3 in cryptic splicing within the context of functional genes and how disease-associated variants impact this function. We show that loss of MATR3 leads to cryptic exon inclusion in many transcripts. We reveal that ALS-linked S85C pathogenic variant reduces MATR3 solubility but does not impair RNA binding. In parallel, we report a novel neurodevelopmental disease-associated M548T variant, located in the RRM2 domain, which reduces protein solubility and impairs RNA binding and cryptic splicing repression functions of MATR3. Altogether, our research identifies cryptic events within functional genes and demonstrates how disease-associated variants impact MATR3 cryptic splicing repression function.

Molecular Pathways and Animal Models of Arrhythmias

Arrhythmias account for over 300,000 annual deaths in the United States, and approximately half of all deaths are associated with heart disease. Mechanisms underlying arrhythmia risk are complex; however, work in humans and animal models over the past 25 years has identified a host of molecular pathways linked with both arrhythmia substrates and triggers. This chapter will focus on select arrhythmia pathways solved by linking human clinical and genetic data with animal models.

Systemic primary carnitine deficiency induces severe arrhythmia due to shortening of QT interval

BACKGROUND

Systemic primary carnitine deficiency (PCD) is characterized by cardiomyopathy and arrhythmia. Without carnitine supplementation, progression is usually towards fatal cardiac decompensation. While the cardiomyopathy is most likely secondary to energy deficiency, the mechanism of arrhythmia is unclear, and may be related to a short QT interval.

OBJECTIVE

We aim to describe rhythmic manifestations at diagnosis and with carnitine supplementation.

METHODS

French patients diagnosed for PCD were retrospectively included. Clinical and para clinical data at diagnosis and during follow-up were collected. Electrocardiograms with QT interval measurements were blinded reviewed by two paediatric cardiologists.

RESULTS

Nineteen patients (median age at diagnosis 2.3 years (extremes 0.3-28.9)) followed in 8 French centres were included. At diagnosis, 21% of patients (4/19) had arrhythmia (2 ventricular fibrillations, 1 ventricular tachycardia and 1 sudden death), and 84% (16/19) had cardiomyopathy. Six electrocardiograms before treatment out of 11 available displayed a short QT (QTc < 340 ms). Median corrected QTc after carnitine supplementation was 404 ms (extremes 341-447) versus 350 ms (extremes 282-421) before treatment (p < 0.001). The whole QTc was prolonged, and no patient reached the criterion of short QT syndrome with carnitine supplementation. Three patients died, probably from rhythmic cause without carnitine supplementation (two extra-hospital sudden deaths and one non-recoverable rhythmic storm before carnitine supplementation), whereas no rhythmic complication occurred in patients with carnitine supplementation.

CONCLUSION

PCD is associated with shortening of the QT interval inducing severe arrhythmia. A potential explanation would be a toxic effect of accumulated fatty acid and metabolites on ionic channels embedded in the cell membrane. Carnitine supplementation normalizes the QTc and prevents arrhythmia. Newborn screening of primary carnitine deficiency would prevent avoidable deaths.

FGF12: biology and function

Fibroblast growth factor 12 (FGF12) belongs to the fibroblast growth factor homologous factors (FHF) subfamily, which is also known as the FGF11 subfamily. The human FGF12 gene is located on chromosome 3 and consists of four introns and five coding exons. Their alternative splicing results in two FGF12 isoforms - the shorter 'b' isoform and the longer 'a' isoform. Structurally, the core domain of FGF12, is highly homologous to that of the other FGF proteins, providing the classical tertiary structure of β-trefoil. FGF12 is expressed in various tissues, most abundantly in excitable cells such as neurons and cardiomyocytes. For many years, FGF12 was thought to be exclusively an intracellular protein, but recent studies have shown that it can be secreted despite the absence of a canonical signal for secretion. The best-studied function of FGF12 relates to its interaction with sodium channels. In addition, FGF12 forms complexes with signaling proteins, regulates the cytoskeletal system, binds to the FGF receptors activating signaling cascades to prevent apoptosis and interacts with the ribosome biogenesis complex. Importantly, FGF12 has been linked to nervous system disorders, cancers and cardiac diseases such as epileptic encephalopathy, pulmonary hypertension and cardiac arrhythmias, making it a potential target for gene therapy as well as a therapeutic agent.

Noncoding RNAs and Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes in Cardiac Arrhythmic Brugada Syndrome

Hundreds of thousands of people die each year as a result of sudden cardiac death, and many are due to heart rhythm disorders. One of the major causes of these arrhythmic events is Brugada syndrome, a cardiac channelopathy that results in abnormal cardiac conduction, severe life-threatening arrhythmias, and, on many occasions, death. This disorder has been associated with mutations and dysfunction of about two dozen genes; however, the majority of the patients do not have a definite cause for the diagnosis of Brugada Syndrome. The protein-coding genes represent only a very small fraction of the mammalian genome, and the majority of the noncoding regions of the genome are actively transcribed. Studies have shown that most of the loci associated with electrophysiological traits are located in noncoding regulatory regions and are expected to affect gene expression dosage and cardiac ion channel function. Noncoding RNAs serve an expanding number of regulatory and other functional roles within the cells, including but not limited to transcriptional, post-transcriptional, and epigenetic regulation. The major noncoding RNAs found in Brugada Syndrome include microRNAs; however, others such as long noncoding RNAs are also identified. They contribute to pathogenesis by interacting with ion channels and/or are detectable as clinical biomarkers. Stem cells have received significant attention in the recent past, and can be differentiated into many different cell types including those in the heart. In addition to contractile and relaxational properties, BrS-relevant electrophysiological phenotypes are also demonstrated in cardiomyocytes differentiated from stem cells induced from adult human cells. In this review, we discuss the current understanding of noncoding regions of the genome and their RNA biology in Brugada Syndrome. We also delve into the role of stem cells, especially human induced pluripotent stem cell-derived cardiac differentiated cells, in the investigation of Brugada syndrome in preclinical and clinical studies.

Patient-specific iPSC-derived cardiomyocytes reveal variable phenotypic severity of Brugada syndrome

BACKGROUND

Brugada syndrome (BrS) is a cardiac channelopathy that can result in sudden cardiac death (SCD). SCN5A is the most frequent gene linked to BrS, but the genotype-phenotype correlations are not completely matched. Clinical phenotypes of a particular SCN5A variant may range from asymptomatic to SCD. Here, we used comparison of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) derived from a SCN5A mutation-positive (D356Y) BrS family with severely affected proband, asymptomatic mutation carriers (AMCs) and healthy controls to investigate this variation.

METHODS

26 iPSC lines were generated from skin fibroblasts using nonintegrated Sendai virus. The generated iPSCs were differentiated into cardiomyocytes using a monolayer-based differentiation protocol.

FINDINGS

D356Y iPSC-CMs exhibited increased beat interval variability, slower depolarization, cardiac arrhythmias, defects of Na+ channel function and irregular Ca2+ signaling, when compared to controls. Importantly, the phenotype severity observed in AMC iPSC-CMs was milder than that of proband iPSC-CMs, an observation exacerbated by flecainide. Interestingly, the iPSC-CMs of the proband exhibited markedly decreased Ca2+ currents in comparison with control and AMC iPSC-CMs. CRISPR/Cas9-mediated genome editing to correct D356Y in proband iPSC-CMs effectively rescued the arrhythmic phenotype and restored Na+ and Ca2+ currents. Moreover, drug screening using established BrS iPSC-CM models demonstrated that quinidine and sotalol possessed antiarrhythmic effects in an individual-dependent manner. Clinically, venous and oral administration of calcium partially reduced the malignant arrhythmic events of the proband in mid-term follow-up.

INTERPRETATION

Patient-specific and genome-edited iPSC-CMs can recapitulate the varying phenotypic severity of BrS. Our findings suggest that preservation of the Ca2+ currents might be a compensatory mechanism to resist arrhythmogenesis in BrS AMCs.

FUNDING

National Key R&D Program of China (2017YFA0103700), National Natural Science Foundation of China (81922006, 81870175), Natural Science Foundation of Zhejiang Province (LD21H020001, LR15H020001), National Natural Science Foundation of China (81970269), Key Research and Development Program of Zhejiang Province (2019C03022) and Natural Science Foundation of Zhejiang Province (LY16H020002).

Genetic analysis identifies the SLC4A3 anion exchanger as a major gene for short QT syndrome

BACKGROUND

A variant in the SLC4A3 anion exchanger has been identified as a novel cause of short QT syndrome (SQTS), but the clinical importance of SLC4A3 as a cause of SQTS or sudden cardiac death remains unknown.

OBJECTIVE

The purpose of this study was to investigate the prevalence of potential disease-causing variants in SQTS patients using gene panels including SLC4A3.

METHODS

In this multicenter study, genetic testing was performed in 34 index patients with SQTS. The pathogenicity of novel SLC4A3variants was validated in a zebrafish embryo heart model.

RESULTS

Potentially disease-causing variants were identified in 9 (26%) patients and were mainly (15%) located in SLC4A3: 4 patients heterozygous for novel nonsynonymous SLC4A3 variants-p.Arg600Cys, p.Arg621Trp, p.Glu852Asp, and p.Arg952His-and 1 patient with the known p.Arg370His variant. In other SQTS genes, potentially disease-causing variants were less frequent (2× in KCNQ1, 1× in KCNJ2, and CACNA1C each). SLC4A3 variant carriers (n = 5) had a similar heart rate but shorter QT and J point to T wave peak intervals than did noncarriers (n = 29). Knockdown of slc4a3 in zebrafish resulted in shortened heart rate-corrected QT intervals (calculated using the Bazett formula) that could be rescued by overexpression of the native human SLC4A3-encoded protein (AE3), but neither by the mutated AE3 variants p.Arg600Cys, p.Arg621Trp, p.Glu852Asp nor by p.Arg952His, suggesting pathogenicity of these variants. Dysfunction in slc4a3/AE3 was associated with alkaline cytosol and shortened action potential of cardiomyocytes.

CONCLUSION

In about a quarter of patients with SQTS, a potentially disease-causing variant can be identified. Nonsynonymous variants in SLC4A3 represent the most common cause of SQTS, underscoring the importance of including SLC4A3 in the genetic screening of patients with SQTS or sudden cardiac death.

Genetic and Molecular Mechanisms in Brugada Syndrome

Brugada syndrome is a rare hereditary arrhythmia disorder characterized by a distinctive electrocardiogram pattern and an elevated risk of ventricular arrhythmias and sudden cardiac death in young adults. Despite recent advances, it remains a complex condition, encompassing mechanisms, genetics, diagnosis, arrhythmia risk stratification, and management. The underlying electrophysiological mechanism of Brugada syndrome requires further investigation, with current theories focusing on abnormalities in repolarization, depolarization, and current-load match. The genetic basis of the syndrome is strong, with mutations found in genes encoding subunits of cardiac sodium, potassium, and calcium channels, as well as genes involved in channel trafficking and regulation. While the initial discovery of mutations in the SCN5A gene provided valuable insights, Brugada syndrome is now recognized as a multifactorial disease influenced by several loci and environmental factors, challenging the traditional autosomal dominant inheritance model. This comprehensive review aims to provide a current understanding of Brugada syndrome, focusing on its pathophysiology, genetic mechanisms, and novel models of risk stratification. Advancements in these areas hold the potential to facilitate earlier diagnosis, improve risk assessments, and enable more targeted therapeutic interventions.

Anesthesia in patients with Brugada syndrome: two case reports

BACKGROUND

Brugada syndrome is a rare disease. It causes sudden cardiac arrest, which is a serious life-threatening event. Sudden cardiac death mostly results from coronary artery disease. However, patients with Brugada syndrome show normal cardiac anatomy and no evidence of ischemia or electrolyte imbalance. Anesthesia in patients with Brugada syndrome is challenging due to its unpredictable nature, and is worth our attention.

CASE PRESENTATION

We report two cases of Brugada syndrome during anesthesia. In case one, a 31-year-old Filipino laborer was scheduled for laparoscopic appendectomy. The patient denied any preexisting cardiac disease. The preoperative vital signs were stable, with mild fever of 37.9 °C. The operation was smooth. During the emergence period, the patient suffered from sudden onset of ventricular tachycardia. After resuscitation, the cardiac rhythm returned to normal. Later, he was confirmed to have a genetic trait of Brugada syndrome. In case two, a young Taiwanese patient with pre-diagnosed Brugada syndrome underwent an operation. The perioperative precautions were taken to prevent the occurrence of ventricular arrhythmia. The surgery was uneventful.

CONCLUSIONS

Brugada syndrome, although rare, has the highest incidence in South East Asian healthy young males. It brings attention to possible fatal cardiac arrhythmia in this population. Careful preoperative evaluation and perioperative management can help reduce the harmful outcome of the disease and prevent any untoward events.

Current updates on arrhythmia within Timothy syndrome: genetics, mechanisms and therapeutics

Timothy syndrome (TS), characterised by multiple system malfunction especially the prolonged corrected QT interval and synchronised appearance of hand/foot syndactyly, is an extremely rare disease affecting early life with devastating arrhythmia. In this work, firstly, the various mutations in causative gene CACNA1C encoding cardiac L-type voltage-gated calcium channel (LTCC), regard with the genetic pathogeny and nomenclature of TS are reviewed. Secondly, the expression profile and function of CACNA1C gene encoding Cav1.2 proteins, and its gain-of-function mutation in TS leading to multiple organ disease phenotypes especially arrhythmia are discussed. More importantly, we focus on the altered molecular mechanism underlying arrhythmia in TS, and discuss about how LTCC malfunction in TS can cause disorganised calcium handling with excessive intracellular calcium and its triggered dysregulated excitation-transcription coupling. In addition, current therapeutics for TS cardiac phenotypes including LTCC blockers, beta-adrenergic blocking agents, sodium channel blocker, multichannel inhibitors and pacemakers are summarised. Eventually, the research strategy using patient-specific induced pluripotent stem cells is recommended as one of the promising future directions for developing therapeutic approaches. This review updates our understanding on the research progress and future avenues to study the genetics and molecular mechanism underlying the pathogenesis of devastating arrhythmia within TS, and provides novel insights for developing therapeutic measures.

Chinese herbal medicine for the treatment of cardiovascular diseases ─ targeting cardiac ion channels

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality, imposing an increasing global health burden. Cardiac ion channels (voltage-gated Na_V, Ca_V, K_Vs, and others) synergistically shape the cardiac action potential (AP) and control the heartbeat. Dysfunction of these channels, due to genetic mutations, transcriptional or post-translational modifications, may disturb the AP and lead to arrhythmia, a major risk for CVD patients. Although there are five classes of anti-arrhythmic drugs available, they can have varying levels of efficacies and side effects on patients, possibly due to the complex pathogenesis of arrhythmias. As an alternative treatment option, Chinese herbal remedies have shown promise in regulating cardiac ion channels and providing anti-arrhythmic effects. In this review, we first discuss the role of cardiac ion channels in maintaining normal heart function and the pathogenesis of CVD, then summarize the classification of Chinese herbal compounds, and elaborate detailed mechanisms of their efficacy in regulating cardiac ion channels and in alleviating arrhythmia and CVD. We also address current limitations and opportunities for developing new anti-CVD drugs based on Chinese herbal medicines.

Sudden cardiac arrest in a patient with malignant mitral valve prolapse with CACNB2 gene mutation: a simple coincidence or coexistence?-a case report

Background

Despite recent advances in cardiology, sudden cardiac death remains to be a significant challenge, and the precise cause for a large proportion of sudden cardiac arrests remains unclear.

Case summary

A 48-year-old fit and healthy medical personnel with no previous medical illness suffered from ventricular fibrillation at his workplace and was successfully resuscitated. Although the basal electrocardiogram did not show a Brugada pattern, we identified mutations in the CACNB2 genes (Chr10: 18150879 and Chr10: 18539538 variants), which are pathogenic variants linked to the Brugada syndrome. A transthoracic echocardiogram and cardiac magnetic resonance revealed mitral valve prolapse (MVP) with characteristics of Barlow's disease, as well as malignant MVP features such as the presence of bileaflet prolapse, mitral annular disjunction, and inferior and inferolateral left ventricular wall fibrosis.

Discussion

To the best of our knowledge, this is the first case report on sudden cardiac arrest in a patient with malignant MVP with a CACNB2 gene mutation. This study highlights the merit for further research to establish standardized criteria for the diagnosis of malignant MVP, for the primary prevention of sudden cardiac death. Cardiac MR should also be part of the diagnostic evaluation of MVP to allow for the early detection of arrhythmogenic features, especially left ventricular fibrosis. We also suggest that the utility of genetic testing should be complementary to the current diagnostic tools for unexplained cardiac arrest and patients with MVP. This would help to better understand the genetic basis between these two conditions for better risk stratification and early cardiac intervention.

Transcriptional Dysregulation Underlies Both Monogenic Arrhythmia Syndrome and Common Modifiers of Cardiac Repolarization

BACKGROUND

Brugada syndrome (BrS) is an inherited arrhythmia syndrome caused by loss-of-function variants in the cardiac sodium channel gene SCN5A (sodium voltage-gated channel alpha subunit 5) in ≈20% of subjects. We identified a family with 4 individuals diagnosed with BrS harboring the rare G145R missense variant in the cardiac transcription factor TBX5 (T-box transcription factor 5) and no SCN5A variant.

METHODS

We generated induced pluripotent stem cells (iPSCs) from 2 members of a family carrying TBX5-G145R and diagnosed with Brugada syndrome. After differentiation to iPSC-derived cardiomyocytes (iPSC-CMs), electrophysiologic characteristics were assessed by voltage- and current-clamp experiments (n=9 to 21 cells per group) and transcriptional differences by RNA sequencing (n=3 samples per group), and compared with iPSC-CMs in which G145R was corrected by CRISPR/Cas9 approaches. The role of platelet-derived growth factor (PDGF)/phosphoinositide 3-kinase (PI3K) pathway was elucidated by small molecule perturbation. The rate-corrected QT (QTc) interval association with serum PDGF was tested in the Framingham Heart Study cohort (n=1893 individuals).

RESULTS

TBX5-G145R reduced transcriptional activity and caused multiple electrophysiologic abnormalities, including decreased peak and enhanced "late" cardiac sodium current (INa), which were entirely corrected by editing G145R to wild-type. Transcriptional profiling and functional assays in genome-unedited and -edited iPSC-CMs showed direct SCN5A down-regulation caused decreased peak INa, and that reduced PDGF receptor (PDGFRA [platelet-derived growth factor receptor α]) expression and blunted signal transduction to PI3K was implicated in enhanced late INa. Tbx5 regulation of the PDGF axis increased arrhythmia risk due to disruption of PDGF signaling and was conserved in murine model systems. PDGF receptor blockade markedly prolonged normal iPSC-CM action potentials and plasma levels of PDGF in the Framingham Heart Study were inversely correlated with the QTc interval (P<0.001).

CONCLUSIONS

These results not only establish decreased SCN5A transcription by the TBX5 variant as a cause of BrS, but also reveal a new general transcriptional mechanism of arrhythmogenesis of enhanced late sodium current caused by reduced PDGF receptor-mediated PI3K signaling.

Frontier and hotspot evolution in Brugada syndrome: A bibliometric analysis from 2002 to 2022

BACKGROUND

Brugada syndrome (BrS) is a genetic disorder characterized by a typical electrocardiogram pattern and predisposition to arrhythmias and sudden cardiac death. Despite our considerably evolved understanding of BrS, no bibliometrics have been performed in this research field. We aimed to analyze and visualize the characteristics of the scientific outputs, topical evolutions, and research trends of BrS over the past 2 decades using bibliometric analysis.

METHODS

The literature associated with BrS was retrieved from the Science Citation Index Expanded of the Web of Science Core Collection database. Acquired data were then visually analyzed using CiteSpace and VOSviewer.

RESULTS

3042 qualifying records were included in the final analysis. The publication outputs increased over time. The United States was the leading country in the BrS research. The University of Amsterdam (Netherlands) was the most prolific and influential institution. Pedro Brugada, Arthur Wilde, and Charles Antzelevitch exerted notable publication impact and made the most significant contributions in the field of BrS. Heart Rhythm had the highest outputs and Circulation was the most influential journal. Bundle branch block, ST-segment elevation, mechanism, management, right precordial lead, and guideline were the keywords with the strongest citation burst.

CONCLUSION

Research on BrS is prosperous. Keywords and co-citation analysis revealed that the mechanism, diagnosis, risk stratification, and management of BrS were the research hotspots. Besides, the underlying pathophysiology, novel therapies, and personalized risk assessment might be the emerging trends of future research.

Palmitoylation of the pore-forming subunit of Ca(v)1.2 controls channel voltage sensitivity and calcium transients in cardiac myocytes

Mammalian voltage-activated L-type Ca2+ channels, such as Ca(v)1.2, control transmembrane Ca2+ fluxes in numerous excitable tissues. Here, we report that the pore-forming α1C subunit of Ca(v)1.2 is reversibly palmitoylated in rat, rabbit, and human ventricular myocytes. We map the palmitoylation sites to two regions of the channel: The N terminus and the linker between domains I and II. Whole-cell voltage clamping revealed a rightward shift of the Ca(v)1.2 current-voltage relationship when α1C was not palmitoylated. To examine function, we expressed dihydropyridine-resistant α1C in human induced pluripotent stem cell-derived cardiomyocytes and measured Ca2+ transients in the presence of nifedipine to block the endogenous channels. The transients generated by unpalmitoylatable channels displayed a similar activation time course but significantly reduced amplitude compared to those generated by wild-type channels. We thus conclude that palmitoylation controls the voltage sensitivity of Ca(v)1.2. Given that the identified Ca(v)1.2 palmitoylation sites are also conserved in most Ca(v)1 isoforms, we propose that palmitoylation of the pore-forming α1C subunit provides a means to regulate the voltage sensitivity of voltage-activated Ca2+ channels in excitable cells.

Modulation of CaV1.2 Channel Function by Interacting Proteins and Post-Translational Modifications: Implications in Cardiovascular Diseases and COVID-19

Ca_V1.2 calcium channel is the primary conduit for Ca²⁺ influx into cardiac and smooth muscles that underscores its importance in the pathogenesis of hypertension, atherosclerosis, myocardial infarction, and heart failure. But, a few controversies still remain. Therefore, exploring new ways to modulate Ca_V1.2 channel activity will augment the arsenal of Ca_V1.2 channel-based therapeutics for treatment of cardiovascular diseases. Here, we will mainly introduce a couple of emerging Ca_V1.2 channel interacting proteins, such as Galectin-1 and Cereblon, and discuss their roles in hypertension and heart failure through fine-tuning Ca_V1.2 channel activity. Of current interest, we will also evaluate the implication of the role of Ca_V1.2 channel in SARS-CoV-2 infection and the potential treatments of COVID-19-related cardiovascular symptoms.

Brugada Syndrome: From Molecular Mechanisms and Genetics to Risk Stratification

Brugada syndrome (BrS) is a rare hereditary arrhythmia disorder, with a distinctive ECG pattern, correlated with an increased risk of ventricular arrhythmias and sudden cardiac death (SCD) in young adults. BrS is a complex entity in terms of mechanisms, genetics, diagnosis, arrhythmia risk stratification, and management. The main electrophysiological mechanism of BrS requires further research, with prevailing theories centered on aberrant repolarization, depolarization, and current-load match. Computational modelling, pre-clinical, and clinical research show that BrS molecular anomalies result in excitation wavelength (k) modifications, which eventually increase the risk of arrhythmia. Although a mutation in the SCN5A (Sodium Voltage-Gated Channel Alpha Subunit 5) gene was first reported almost two decades ago, BrS is still currently regarded as a Mendelian condition inherited in an autosomal dominant manner with incomplete penetrance, despite the recent developments in the field of genetics and the latest hypothesis of additional inheritance pathways proposing a more complex mode of inheritance. In spite of the extensive use of the next-generation sequencing (NGS) technique with high coverage, genetics remains unexplained in a number of clinically confirmed cases. Except for the SCN5A which encodes the cardiac sodium channel NaV1.5, susceptibility genes remain mostly unidentified. The predominance of cardiac transcription factor loci suggests that transcriptional regulation is essential to the Brugada syndrome's pathogenesis. It appears that BrS is a multifactorial disease, which is influenced by several loci, each of which is affected by the environment. The primary challenge in individuals with a BrS type 1 ECG is to identify those who are at risk for sudden death, researchers propose the use of a multiparametric clinical and instrumental strategy for risk stratification. The aim of this review is to summarize the latest findings addressing the genetic architecture of BrS and to provide novel perspectives into its molecular underpinnings and novel models of risk stratification.

β subunits of voltage-gated calcium channels in cardiovascular diseases

Calcium signaling is required in bodily functions essential for survival, such as muscle contractions and neuronal communications. Of note, the voltage-gated calcium channels (VGCCs) expressed on muscle and neuronal cells, as well as some endocrine cells, are transmembrane protein complexes that allow for the selective entry of calcium ions into the cells. The α1 subunit constitutes the main pore-forming subunit that opens in response to membrane depolarization, and its biophysical functions are regulated by various auxiliary subunits-β, α2δ, and γ subunits. Within the cardiovascular system, the γ-subunit is not expressed and is therefore not discussed in this review. Because the α1 subunit is the pore-forming subunit, it is a prominent druggable target and the focus of many studies investigating potential therapeutic interventions for cardiovascular diseases. While this may be true, it should be noted that the direct inhibition of the α1 subunit may result in limited long-term cardiovascular benefits coupled with undesirable side effects, and that its expression and biophysical properties may depend largely on its auxiliary subunits. Indeed, the α2δ subunit has been reported to be essential for the membrane trafficking and expression of the α1 subunit. Furthermore, the β subunit not only prevents proteasomal degradation of the α1 subunit, but also directly modulates the biophysical properties of the α1 subunit, such as its voltage-dependent activities and open probabilities. More importantly, various isoforms of the β subunit have been found to differentially modulate the α1 subunit, and post-translational modifications of the β subunits further add to this complexity. These data suggest the possibility of the β subunit as a therapeutic target in cardiovascular diseases. However, emerging studies have reported the presence of cardiomyocyte membrane α1 subunit trafficking and expression in a β subunit-independent manner, which would undermine the efficacy of β subunit-targeting drugs. Nevertheless, a better understanding of the auxiliary β subunit would provide a more holistic approach when targeting the calcium channel complexes in treating cardiovascular diseases. Therefore, this review focuses on the post-translational modifications of the β subunit, as well as its role as an auxiliary subunit in modulating the calcium channel complexes.

Role of Ca2+ in healthy and pathologic cardiac function: from normal excitation-contraction coupling to mutations that cause inherited arrhythmia

Calcium (Ca²⁺) ions are a key second messenger involved in the rhythmic excitation and contraction of cardiomyocytes throughout the heart. Proper function of Ca²⁺-handling proteins is required for healthy cardiac function, whereas disruption in any of these can cause cardiac arrhythmias. This comprehensive review provides a broad overview of the roles of Ca²⁺-handling proteins and their regulators in healthy cardiac function and the mechanisms by which mutations in these proteins contribute to inherited arrhythmias. Major Ca²⁺ channels and Ca²⁺-sensitive regulatory proteins involved in cardiac excitation-contraction coupling are discussed, with special emphasis on the function of the RyR2 macromolecular complex. Inherited arrhythmia disorders including catecholaminergic polymorphic ventricular tachycardia, long QT syndrome, Brugada syndrome, short QT syndrome, and arrhythmogenic right-ventricular cardiomyopathy are discussed with particular emphasis on subtypes caused by mutations in Ca²⁺-handling proteins.

CACNA1C-Related Channelopathies

The CACNA1C gene encodes the pore-forming subunit of the CaV1.2 L-type Ca2+ channel, a critical component of membrane physiology in multiple tissues, including the heart, brain, and immune system. As such, mutations altering the function of these channels have the potential to impact a wide array of cellular functions. The first mutations identified within CACNA1C were shown to cause a severe, multisystem disorder known as Timothy syndrome (TS), which is characterized by neurodevelopmental deficits, long-QT syndrome, life-threatening cardiac arrhythmias, craniofacial abnormalities, and immune deficits. Since this initial description, the number and variety of disease-associated mutations identified in CACNA1C have grown tremendously, expanding the range of phenotypes observed in affected patients. CACNA1C channelopathies are now known to encompass multisystem phenotypes as described in TS, as well as more selective phenotypes where patients may exhibit predominantly cardiac or neurological symptoms. Here, we review the impact of genetic mutations on CaV1.2 function and the resultant physiological consequences.

Cav1.4 congenital stationary night blindness is associated with an increased rate of proteasomal degradation

Pathogenic, generally loss-of-function, variants in CACNA1F, encoding the Ca_v1.4α₁ calcium channel, underlie congenital stationary night blindness type 2 (CSNB2), a rare inherited retinal disorder associated with visual disability. To establish the underlying pathomechanism, we investigated 10 clinically derived CACNA1F missense variants located across pore-forming domains, connecting loops, and the carboxy-tail domain of the Ca_v1.4α subunit. Homology modeling showed that all variants cause steric clashes; informatics analysis correctly predicted pathogenicity for 7/10 variants. In vitro analyses demonstrated that all variants cause a decrease in current, global expression, and protein stability and act through a loss-of-function mechanism and suggested that the mutant Ca_v1.4α proteins were degraded by the proteasome. We showed that the reduced current for these variants could be significantly increased through treatment with clinical proteasome inhibitors. In addition to facilitating clinical interpretation, these studies suggest that proteasomal inhibition represents an avenue of potential therapeutic intervention for CSNB2.

Epigenetic mechanism of L-type calcium channel β-subunit downregulation in short QT human induced pluripotent stem cell-derived cardiomyocytes with CACNB2 mutation

AIMS

A loss-of-function mutation in L-type calcium (Ca2+) channel subunit gene CACNB2 has been reported to cause short QT syndrome subtype 5 (SQT5). However, the mechanism underlying the loss-of-function of the Ca2+ channel has not been clarified. In the present study, we aim to explore the DNA methylation mechanism of L-type Ca2+ channel downregulation in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) of SQT5.

METHODS AND RESULTS

The hiPSC-CMs were generated from a healthy donor and a SQT5 patient carrying the CACNB2 variant c.1439C > T/p.S480L. The variant was genetically corrected using ribonucleoprotein-based CRISPR/Cas9 technique to obtain an isogenic control cell line. The action potential (AP) and Ca2+ current were measured by patch clamp. Protein expression levels were determined by western blotting. Dot blotting and bisulfite sequence were performed for epigenetic study. Our results showed that AP durations at 10% repolarization (APD10) and 50% repolarization (APD50) were significantly shortened in SQT5 cells and both the expression level of the β-subunit and channel current of L-type Ca2+ channel were reduced. Besides, an increased level of whole-genome DNA methylation and DNA methylation of CpG island in the promoter region of CACNB2 gene was detected. Overexpression of demethylation enzyme could rescue the decreased expression of CACNB2 and the L-type Ca2+ current.

CONCLUSION

In SQT5 hiPSC-CMs carrying the CACNB2-S480L variant, the decreased L-type Ca2+ current resulting from decreased CACNB2 protein expression was caused by enhanced methylation in the promoter region of the CACNB2 gene and upregulation of DNA methyltransferases might be one of the mechanisms.

Exercise-induced Brugada pattern and ventricular tachycardia during Capecitabine treatment

We report the case of a 59-year-old female patient with no previous cardiovascular disease treated for Breast cancer with Capecitabine. Shortly after starting treatment, she developed recurrent angina. An exercise stress echocardiogram was performed, which induced a type 1 Brugada pattern 12 s of a non-sustained pleomorphic ventricular tachycardia ensued.

Computational analysis of arrhythmogenesis in KCNH2 T618I mutation-associated short QT syndrome and the pharmacological effects of quinidine and sotalol

Short QT syndrome (SQTS) is a rare but dangerous genetic disease. In this research, we conducted a comprehensive in silico investigation into the arrhythmogenesis in KCNH2 T618I-associated SQTS using a multi-scale human ventricle model. A Markov chain model of I_Kr was developed firstly to reproduce the experimental observations. It was then incorporated into cell, tissue, and organ models to explore how the mutation provided substrates for ventricular arrhythmias. Using this T618I Markov model, we explicitly revealed the subcellular level functional alterations by T618I mutation, particularly the changes of ion channel states that are difficult to demonstrate in wet experiments. The following tissue and organ models also successfully reproduced the changed dynamics of reentrant spiral waves and impaired rate adaptions in hearts of T618I mutation. In terms of pharmacotherapy, we replicated the different effects of a drug under various conditions using identical mathematical descriptions for drugs. This study not only simulated the actions of an effective drug (quinidine) at various physiological levels, but also elucidated why the I_Kr inhibitor sotalol failed in SQT1 patients through profoundly analyzing its mutation-dependent actions.

Concealed Substrates in Brugada Syndrome: Isolated Channelopathy or Associated Cardiomyopathy?

Brugada syndrome (BrS) is an inherited autosomal dominant genetic disorder responsible for sudden cardiac death from malignant ventricular arrhythmia. The term “channelopathy” is nowadays used to classify BrS as a purely electrical disease, mainly occurring secondarily to loss-of-function mutations in the α subunit of the cardiac sodium channel protein Nav1.5. In this setting, arrhythmic manifestations of the disease have been reported in the absence of any apparent structural heart disease or cardiomyopathy. Over the last few years, however, a consistent amount of evidence has grown in support of myocardial structural and functional abnormalities in patients with BrS. In detail, abnormal ventricular dimensions, either systolic or diastolic dysfunctions, regional wall motion abnormalities, myocardial fibrosis, and active inflammatory foci have been frequently described, pointing to alternative mechanisms of arrhythmogenesis which challenge the definition of channelopathy. The present review aims to depict the status of the art of concealed arrhythmogenic substrates in BrS, often resulting from an advanced and multimodal diagnostic workup, to foster future preclinical and clinical research in support of the cardiomyopathic nature of the disease.

ARumenamides: A novel class of potential antiarrhythmic compounds

Background: Most therapeutics targeting cardiac voltage-gated sodium channels (Nav1.5) attenuate the sodium current (INa) conducted through the pore of the protein. Whereas these drugs may be beneficial for disease states associated with gain-of-function (GoF) in Nav1.5, few attempts have been made to therapeutically treat loss-of-function (LoF) conditions. The primary impediment to designing efficacious therapies for LoF is a tendency for drugs to occlude the Nav1.5 central pore. We hypothesized that molecular candidates with a high affinity for the fenestrations would potentially reduce pore block.

Methods and Results: Virtual docking was performed on 21 compounds, selected based on their affinity for the fenestrations in Nav1.5, which included a class of sulfonamides and carboxamides we identify as ARumenamide (AR). Six ARs, AR-051, AR-189, AR-674, AR-802, AR-807 and AR-811, were further docked against Nav1.5 built on NavAb and rNav1.5. Based on the virtual docking results, these particular ARs have a high affinity for Domain III-IV and Domain VI-I fenestrations. Upon functional characterization, a trend was observed in the effects of the six ARs on INa. An inverse correlation was established between the aromaticity of the AR’s functional moieties and compound block. Due to its aromaticity, AR-811 blocked INa the least compared with other aromatic ARs, which also decelerated fast inactivation onset. AR-674, with its aliphatic functional group, significantly suppresses INa and enhances use-dependence in Nav1.5. AR-802 and AR-811, in particular, decelerated fast inactivation kinetics in the most common Brugada Syndrome Type 1 and Long-QT Syndrome Type 3 mutant, E1784K, without affecting peak or persistent INa.

Conclusion: Our hypothesis that LoF in Nav1.5 may be therapeutically treated was supported by the discovery of ARs, which appear to preferentially block the fenestrations. ARs with aromatic functional groups as opposed to aliphatic groups efficaciously maintained Nav1.5 availability. We predict that these bulkier side groups may have a higher affinity for the hydrophobic milieu of the fenestrations, remaining there rather than in the central pore of the channel. Future refinements of AR compound structures and additional validation by molecular dynamic simulations and screening against more Brugada variants will further support their potential benefits in treating certain LoF cardiac arrhythmias.

Regulation of cardiac ion channels by transcription factors: Looking for new opportunities of druggable targets for the treatment of arrhythmias

Cardiac electrical activity is governed by different ion channels that generate action potentials. Acquired or inherited abnormalities in the expression and/or function of ion channels usually result in electrophysiological changes that can cause cardiac arrhythmias. Transcription factors (TFs) control gene transcription by binding to specific DNA sequences adjacent to target genes. Linkage analysis, candidate-gene screening within families, and genome-wide association studies have linked rare and common genetic variants in the genes encoding TFs with genetically-determined cardiac arrhythmias. Besides its critical role in cardiac development, recent data demonstrated that they control cardiac electrical activity through the direct regulation of the expression and function of cardiac ion channels in adult hearts. This narrative review summarizes some studies showing functional data on regulation of the main human atrial and ventricular Na⁺, Ca²⁺, and K⁺ channels by cardiac TFs such as Pitx2c, Tbx20, Tbx5, Zfhx3, among others. The results have improved our understanding of the mechanisms regulating cardiac electrical activity and may open new avenues for therapeutic interventions in cardiac acquired or inherited arrhythmias through the identification of TFs as potential drug targets. Even though TFs have for a long time been considered as 'undruggable' targets, advances in structural biology have led to the identification of unique pockets in TFs amenable to be targeted with small-molecule drugs or peptides that are emerging as novel therapeutic drugs.

A Preclinical Study on Brugada Syndrome with a CACNB2 Variant Using Human Cardiomyocytes from Induced Pluripotent Stem Cells

Aims: Some gene variants in the sodium channels, as well as calcium channels, have been associated with Brugada syndrome (BrS). However, the investigation of the human cellular phenotype and the use of drugs for BrS in presence of variant in the calcium channel subunit is still lacking. Objectives: The objective of this study was to establish a cellular model of BrS in the presence of a CACNB2 variant of uncertain significance (c.425C > T/p.S142F) using human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and test drug effects using this model. Methods and results: This study recruited cells from a patient with Brugada syndrome (BrS) and recurrent ventricular fibrillation carrying a missense variant in CACNB2 as well as from three healthy independent persons. These cells (hiPSC-CMs) generated from skin biopsies of healthy persons and the BrS patient (BrS-hiPSC-CMs) as well as CRISPR/Cas9 corrected cells (isogenic control, site-variant corrected) were used for this study. The hiPSC-CMs from the BrS patient showed a significantly reduced L-type calcium channel current (ICa-L) compared with the healthy control hiPSC-CMs. The inactivation curve was shifted to a more positive potential and the recovery from inactivation was accelerated. The protein expression of CACNB2 of the hiPSC-CMs from the BrS-patient was significantly decreased compared with healthy hiPSC-CMs. Moreover, the correction of the CACNB2 site-variant rescued the changes seen in the hiPSC-CMs of the BrS patient to the normal state. These data indicate that the CACNB2 gene variant led to loss-of-function of L-type calcium channels in hiPSC-CMs from the BrS patient. Strikingly, arrhythmia events were more frequently detected in BrS-hiPSC-CMs. Bisoprolol (beta-blockers) at low concentration and quinidine decreased arrhythmic events. Conclusions: The CACNB2 variant (c.425C > T/p.S142F) causes a loss-of-function of L-type calcium channels and is pathogenic for this type of BrS. Bisoprolol and quinidine may be effective for treating BrS with this variant.

Novel CACNA1C R511Q mutation, located in domain Ⅰ-Ⅱ linker, causes non-syndromic type-8 long QT syndrome

Background

Gain-of-function mutations in CACNA1C encoding Cav1.2 cause syndromic or non-syndromic type-8 long QT syndrome (LQTS) (sLQT8 or nsLQT8). The cytoplasmic domain (D)Ⅰ-Ⅱ linker in Cav1.2 plays a pivotal role in calcium channel inactivation, and mutations in this site have been associated with sLQT8 (such as Timothy syndrome) but not nsLQT8.

Objective

Since we identified a novel CACNA1C mutation, located in the DⅠ-Ⅱ linker, associated with nsLQTS, we sought to reveal its biophysical defects.

Methods

Target panel sequencing was employed in 24 genotype-negative nsLQTS probands (after Sanger sequencing) and three family members. Wild-type (WT) or R511Q Cav1.2 was transiently expressed in tsA201 cells, then whole-cell Ca²⁺ or Ba²⁺ currents (I_Ca or I_Ba) were recorded using whole-cell patch-clamp techniques.

Results

We identified two CACNA1C mutations, a previously reported R858H mutation and a novel R511Q mutation located in the DⅠ-Ⅱ linker. Four members of one nsLQTS family harbored the CACNA1C R511Q mutation. The current density and steady-state activation were comparable to those of WT-I_Ca. However, persistent currents in R511Q-I_Ca were significantly larger than those of WT-I_Ca (WT at +20 mV: 3.3±0.3%, R511Q: 10.8±0.8%, P<0.01). The steady-state inactivation of R511Q-I_Ca was weak in comparison to that of WT-I_Ca at higher prepulse potentials, resulting in increased window currents in R511Q-I_Ca. Slow component of inactivation of R511Q-I_Ca was significantly delayed compared to that of WT-I_Ca (WT-tau at +20 mV: 81.3±3.3 ms, R511Q-tau: 125.1±5.0 ms, P<0.01). Inactivation of R511Q-I_Ba was still slower than that of WT-I_Ba, indicating that voltage-dependent inactivation (VDI) of R511Q-I_Ca was predominantly delayed.

Conclusions

Delayed VDI, increased persistent currents, and increased window currents of R511Q-I_Ca cause nsLQT8. Our data provide novel insights into the structure-function relationships of Cav1.2 and the pathophysiological roles of the DⅠ-Ⅱ linker in phenotypic manifestations.

Exercise in the Genetic Arrhythmia Syndromes - A Review

Provide a brief summary of your article (100-150 words; no references or figures/tables). The synopsis appears only in the table of contents and is often used by indexing services such as PubMed. Genetic arrhythmia syndromes are rare, yet harbor the potential for highly consequential, often unpredictable arrhythmias or sudden death events. There has been historical uncertainty regarding the correct advice to offer to affected patients who are reasonably wanting to participate in sporting and athletic endeavors. In some cases, this had led to abundantly cautious disqualifications, depriving individuals from participation unnecessarily. Societal guidance and expert opinion has evolved significantly over the last decade or 2, along with our understanding of the genetics and natural history of these conditions, and the emphasis has switched toward shared decision making with respect to the decision to participate or not, with patients and families becoming better informed, and willing participants in the decision making process. This review aims to give a brief update of the salient issues for the busy physician concerning these syndromes and to provide a framework for approaching their management in the otherwise aspirational or keen sports participant.

The Genetics and Epigenetics of Ventricular Arrhythmias in Patients Without Structural Heart Disease

Ventricular arrhythmia without structural heart disease is an arrhythmic disorder that occurs in structurally normal heart and no transient or reversible arrhythmia factors, such as electrolyte disorders and myocardial ischemia. Ventricular arrhythmias without structural heart disease can be induced by multiple factors, including genetics and environment, which involve different genetic and epigenetic regulation. Familial genetic analysis reveals that cardiac ion-channel disorder and dysfunctional calcium handling are two major causes of this type of heart disease. Genome-wide association studies have identified some genetic susceptibility loci associated with ventricular tachycardia and ventricular fibrillation, yet relatively few loci associated with no structural heart disease. The effects of epigenetics on the ventricular arrhythmias susceptibility genes, involving non-coding RNAs, DNA methylation and other regulatory mechanisms, are gradually being revealed. This article aims to review the knowledge of ventricular arrhythmia without structural heart disease in genetics, and summarizes the current state of epigenetic regulation.

Inhibitory effects on L- and N-type calcium channels by a novel CaVβ1 variant identified in a patient with autism spectrum disorder

Voltage-gated calcium channel (VGCC) subunits have been genetically associated with autism spectrum disorders (ASD). The properties of the pore-forming VGCC subunit are modulated by auxiliary β-subunits, which exist in four isoforms (Ca_Vβ_1-4). Our previous findings suggested that activation of L-type VGCCs is a common feature of Ca_Vβ₂ subunit mutations found in ASD patients. In the current study, we functionally characterized a novel Ca_Vβ_1b variant (p.R296C) identified in an ASD patient. We used whole-cell and single-channel patch clamp to study the effect of Ca_Vβ_{1b_R296C} on the function of L- and N-type VGCCs. Furthermore, we used co-immunoprecipitation followed by Western blot to evaluate the interaction of the Ca_Vβ_1b-subunits with the RGK-protein Gem. Our data obtained at both, whole-cell and single-channel levels, show that compared to a wild-type Ca_Vβ_1b, the Ca_Vβ_{1b_R296C} variant inhibits L- and N-type VGCCs. Interaction with and modulation by the RGK-protein Gem seems to be intact. Our findings indicate functional effects of the Ca_Vβ_{1b_R296C} variant differing from that attributed to Ca_Vβ₂ variants found in ASD patients. Further studies have to detail the effects on different VGCC subtypes and on VGCC expression.

Brugada Syndrome: Different Experimental Models and the Role of Human Cardiomyocytes From Induced Pluripotent Stem Cells

Brugada syndrome (BrS) is an inherited and rare cardiac arrhythmogenic disease associated with an increased risk of ventricular fibrillation and sudden cardiac death. Different genes have been linked to BrS. The majority of mutations are located in the SCN5A gene, and the typical abnormal ECG is an elevation of the ST segment in the right precordial leads V1 to V3. The pathophysiological mechanisms of BrS were studied in different models, including animal models, heterologous expression systems, and human-induced pluripotent stem cell-derived cardiomyocyte models. Currently, only a few BrS studies have used human-induced pluripotent stem cell-derived cardiomyocytes, most of which have focused on genotype-phenotype correlations and drug screening. The combination of new technologies, such as clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 (CRISPR associated protein 9)-mediated genome editing and 3-dimensional engineered heart tissues, has provided novel insights into the pathophysiological mechanisms of the disease and could offer opportunities to improve the diagnosis and treatment of patients with BrS. This review aimed to compare different models of BrS for a better understanding of the roles of human-induced pluripotent stem cell-derived cardiomyocytes in current BrS research and personalized medicine at a later stage.

Identification of ultra-rare disruptive variants in voltage-gated calcium channel-encoding genes in Japanese samples of schizophrenia and autism spectrum disorder

Several large-scale whole-exome sequencing studies in patients with schizophrenia (SCZ) and autism spectrum disorder (ASD) have identified rare variants with modest or strong effect size as genetic risk factors. Dysregulation of cellular calcium homeostasis might be involved in SCZ/ASD pathogenesis, and genes encoding L-type voltage-gated calcium channel (VGCC) subunits Ca_v1.1 (CACNA1S), Ca_v1.2 (CACNA1C), Ca_v1.3 (CACNA1D), and T-type VGCC subunit Ca_v3.3 (CACNA1I) recently were identified as risk loci for psychiatric disorders. We performed a screening study, using the Ion Torrent Personal Genome Machine (PGM), of exon regions of these four candidate genes (CACNA1C, CACNA1D, CACNA1S, CACNA1I) in 370 Japanese patients with SCZ and 192 with ASD. Variant filtering was applied to identify biologically relevant mutations that were not registered in the dbSNP database or that have a minor allele frequency of less than 1% in East-Asian samples from databases; and are potentially disruptive, including nonsense, frameshift, canonical splicing site single nucleotide variants (SNVs), and non-synonymous SNVs predicted as damaging by five different in silico analyses. Each of these filtered mutations were confirmed by Sanger sequencing. If parental samples were available, segregation analysis was employed for measuring the inheritance pattern. Using our filter, we discovered one nonsense SNV (p.C1451* in CACNA1D), one de novo SNV (p.A36V in CACNA1C), one rare short deletion (p.E1675del in CACNA1D), and 14 NSstrict SNVs (non-synonymous SNV predicted as damaging by all of five in silico analyses). Neither p.A36V in CACNA1C nor p.C1451* in CACNA1D were found in 1871 SCZ cases, 380 ASD cases, or 1916 healthy controls in the independent sample set, suggesting that these SNVs might be ultra-rare SNVs in the Japanese population. The neuronal splicing isoform of Ca_v1.2 with the p.A36V mutation, discovered in the present study, showed reduced Ca²⁺-dependent inhibition, resulting in excessive Ca²⁺ entry through the mutant channel. These results suggested that this de novo SNV in CACNA1C might predispose to SCZ by affecting Ca²⁺ homeostasis. Thus, our analysis successfully identified several ultra-rare and potentially disruptive gene variants, lending partial support to the hypothesis that VGCC-encoding genes may contribute to the risk of SCZ/ASD.

A descriptive report on short QT interval in Kherameh branch of the PERSIAN cohort study

Short QT-interval is a condition that bear the suspicion of short QT syndrome (SQTS). SQTS is known to increase risk of life-threatening arrythmias and sudden cardiac death (SCD). Due to the insufficient population-based studies and use of various QT cut-off values, it accounts for as an undiagnosed condition. In this study, we sought for prevalence of short QT interval in Kherameh cohort study, one of the southern branches of the Prospective Epidemiological Research Studies in Iran (PERSIAN). Data of 4363 adult subjects were analyzed from phase 1 of the cohort during 2014–2017. The corrected QT (QTc) intervals were calculated and electrocardiograms (ECGs) with QTc of less than 370 ms (msec) were reanalyzed for bradycardia, early repolarization, atrial fibrillation (AF), arrhythmias, and other electrical conduction abnormalities. Seventy-two subjects (1.65%) had a QTc of less than 370 ms (mean QTc of 360.72 ± 11.72). A male predominance and a lower mean heart rate observed in SQTS susceptible group (M/F of 1/0.26 vs. 1/1.145, p-value < 0.0001; 58.389 ± 9.787 vs. 70.899 ± 11.775; p-value < 0.0001) compare to the subjects with normal QTc. At least, 2 subjects with high-probability SQTS and 3 with intermediate-probability SQTS identified. The frequency of AF, syncope, bradycardia, early repolarization, low voltage ECG, and infantile SCD in first- and second-degree relatives were 16.67, 4.17, 33.33, 11.11, 11.11, 11.11%, respectively. The prevalence of short QT interval in our cohort was in line with previous studies. The incidence of cardiac symptoms/events, familial SCDs and ECG derived specific findings were high amongst SQTS-susceptible index persons. However, these variables could not predict the symptomatic subjects, which emphasizes gene studies and family screening.

The role of CACNA1C in Brugada syndrome: prevalence and phenotype of probands referred for genetic testing

BACKGROUND

Contradictory evidence is available on the role of the CACNA1C gene, encoding for the α-subunit of the cardiac L-type calcium channel (CaV1.2), as a cause of the BrS3 variant of Brugada syndrome (BrS).

OBJECTIVE

We aimed at tackling this issue in a large BrS cohort to define the yield of molecular screening and to address the hypothesis if an appropriate patient selection could improve the clinical utility.

METHODS

A total of 709 patients entered this study. BrS probands (n= 563, consecutively referred) underwent CACNA1C sequencing. Two matched cohorts where defined: discovery cohort (n = 200 patients) and confirmation cohort (n = 363 patients). Furthermore, the clinical phenotypes of a matched SCN5A positive BrS cohort (n= 146) were included for comparative genotype-phenotype correlation.

RESULTS

In the discovery cohort, we identified 11 different rare variants in 9 patients of whom 10 (5%) were considered potentially causative based on their frequency in the general population. However, ACMG criteria were unable to classify the majority (80%) of them eventually labeled as variants of unknown significance (VUS). Functional studies revealed a loss of function for 9 variants pointing to a prevalence of CACNA1C causative variants in 4% in the discovery cohort. Genotype-phenotype correlation showed that pathogenic variants are significantly more frequent in patients with a shorter QTc (12.9 % vs 2.2 % in patients with QTc < 390 ms).

CONCLUSION

CACNA1C is an infrequent but definitive cause of BrS typically associated with short QT. Functional studies are highly relevant to improve variant interpretation.

Circulatory MicroRNAs in Plasma and Atrial Fibrillation in the General Population: The Rotterdam Study

Background: MicroRNAs (miRNAs), small non-coding RNAs regulating gene expression, have been shown to play an important role in cardiovascular disease. However, limited population-based data regarding the relationship between circulatory miRNAs in plasma and atrial fibrillation (AF) exist. Moreover, it remains unclear if the relationship differs by sex. We therefore aimed to determine the (sex-specific) association between plasma circulatory miRNAs and AF at the population level. Methods: Plasma levels of miRNAs were measured using a targeted next-generation sequencing method in 1999 participants from the population-based Rotterdam Study. Logistic regression and Cox proportional hazards models were used to assess the associations of 591 well-expressed miRNAs with the prevalence and incidence of AF. Models were adjusted for cardiovascular risk factors. We further examined the link between predicted target genes of the identified miRNAs. Results: The mean age was 71.7 years (57.1% women), 98 participants (58 men and 40 women) had prevalent AF at baseline. Moreover, 196 participants (96 men and 100 women) developed AF during a median follow-up of 9.0 years. After adjusting for multiple testing, miR-4798-3p was significantly associated with the odds of prevalent AF among men (odds ratio, 95% confidence interval, 0.39, 0.24–0.66, p-value = 0.000248). No miRNAs were significantly associated with incident AF. MiR-4798-3p could potentially regulate the expression of a number of AF-related genes, including genes involved in calcium and potassium handling in myocytes, protection of cells against oxidative stress, and cardiac fibrosis. Conclusions: Plasma levels of miR-4798-3p were significantly associated with the odds of prevalent AF among men. Several target genes in relation to AF pathophysiology could potentially be regulated by miR-4798-3p that warrant further investigations in future experimental studies.

Personalized medicine in cardiovascular disease: review of literature

Purpose

Personalized medicine (PM) is the concept of managing patients based on their characteristics, including genotypes. In the field of cardiology, advantages of PM could be found in the diagnosis and treatment of several conditions such as arrhythmias and cardiomyopathies; moreover, it may be beneficial to prevent adverse drug reactions (ADR) and select the best medication. Genetic background can help us in selecting effective treatments, appropriate dose requirements, and preventive strategies in individuals with particular genotypes.

Method

In this review, we provide examples of personalized medicine based on human genetics for the most used pharmaceutics in cardiology, including warfarin, clopidogrel, and statins. We also review cardiovascular diseases, including coronary artery disease, arrhythmia, and cardiomyopathies.

Conclusion

Genetic factors are as important as environmental factors and they should be tested and evaluated more in the future by improving in genetic testing tools.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-021-00840-0.

Androgens, QT, sex and ventricular repolarization-a double-edged sword: A case series

The prevalence and incidence of cardiac pro-arrhythmic disorders are often influenced by sex due to specific effects on the QT interval. Androgens shorten QT, which may be protective against acquired long QT syndromes and their related arrhythmias in men such as torsade de pointes (TdP). On the other hand, androgens can potentiate Brugada and early repolarization syndromes, which are most prevalent in men. In this case series, we highlight four male patients with aborted SCD in the setting of abnormal testosterone status; two patients with TdP in a setting of testosterone deprivation (of which one drug-induced) and 2 patients with ventricular fibrillation associated with exogenous androgenic booster (Tribulus terrestris) intake. From this case series, we review the current available literature of the effects of androgen as a double-edged sword on the QTc interval and emphasize the importance of QTc monitoring in this subset of patients.

Electrocardiographic Scaling Reveals Differences in Electrocardiogram Interval Durations Between Marine and Terrestrial Mammals

Although the ability of marine mammals to lower heart rates for extended periods when diving is well documented, it is unclear whether marine mammals have electrophysiological adaptations that extend beyond overall bradycardia. We analyzed electrocardiographic data from 50 species of terrestrial mammals and 19 species of marine mammals to determine whether the electrical activity of the heart differs between these two groups of mammals. We also tested whether physiological state (i.e., anesthetized or conscious) affects electrocardiogram (ECG) parameters. Analyses of ECG waveform morphology (heart rate, P-wave duration, and PQ, PR, QRS, and QT intervals) revealed allometric relationships between body mass and all ECG intervals (as well as heart rate) for both groups of mammals and specific differences in ECG parameters between marine mammals and their terrestrial counterparts. Model outputs indicated that marine mammals had 19% longer P-waves, 24% longer QRS intervals, and 21% shorter QT intervals. In other words, marine mammals had slower atrial and ventricular depolarization, and faster ventricular repolarization than terrestrial mammals. Heart rates and PR intervals were not significantly different between marine and terrestrial mammals, and physiological state did not significantly affect any ECG parameter. On average, ECG interval durations of marine and terrestrial mammals scaled with body mass to the power of 0.21 (range: 0.19–0.23) rather than the expected 0.25—while heart rate scaled with body mass to the power of –0.22 and was greater than the widely accepted –0.25 derived from fractal geometry. Our findings show clear differences between the hearts of terrestrial and marine mammals in terms of cardiac timing that extend beyond diving bradycardia. They also highlight the importance of considering special adaptations (such as breath-hold diving) when analyzing allometric relationships.

Ventricular voltage-gated ion channels: Detection, characteristics, mechanisms, and drug safety evaluation

Cardiac voltage-gated ion channels (VGICs) play critical roles in mediating cardiac electrophysiological signals, such as action potentials, to maintain normal heart excitability and contraction. Inherited or acquired alterations in the structure, expression, or function of VGICs, as well as VGIC-related side effects of pharmaceutical drug delivery can result in abnormal cellular electrophysiological processes that induce life-threatening cardiac arrhythmias or even sudden cardiac death. Hence, to reduce possible heart-related risks, VGICs must be acknowledged as important targets in drug discovery and safety studies related to cardiac disease. In this review, we first summarize the development and application of electrophysiological techniques that are employed in cardiac VGIC studies alone or in combination with other techniques such as cryoelectron microscopy, optical imaging and optogenetics. Subsequently, we describe the characteristics, structure, mechanisms, and functions of various well-studied VGICs in ventricular myocytes and analyze their roles in and contributions to both physiological cardiac excitability and inherited cardiac diseases. Finally, we address the implications of the structure and function of ventricular VGICs for drug safety evaluation. In summary, multidisciplinary studies on VGICs help researchers discover potential targets of VGICs and novel VGICs in heart, enrich their knowledge of the properties and functions, determine the operation mechanisms of pathological VGICs, and introduce groundbreaking trends in drug therapy strategies, and drug safety evaluation.

Sensitivity Analysis of Ion Channel Conductance on Myocardial Electromechanical Delay: Computational Study

It is well known that cardiac electromechanical delay (EMD) can cause dyssynchronous heart failure (DHF), a prominent cardiovascular disease (CVD). This work computationally assesses the conductance variation of every ion channel on the cardiac cell to give rise to EMD prolongation. The electrical and mechanical models of human ventricular tissue were simulated, using a population approach with four conductance reductions for each ion channel. Then, EMD was calculated by determining the difference between the onset of action potential and the start of cell shortening. Finally, EMD data were put into the optimized conductance dimensional stacking to show which ion channel has the most influence in elongating the EMD. We found that major ion channels, such as L-type calcium (CaL), slow-delayed rectifier potassium (Ks), rapid-delayed rectifier potassium (Kr), and inward rectifier potassium (K1), can significantly extend the action potential duration (APD) up to 580 ms. Additionally, the maximum intracellular calcium (Cai) concentration is greatly affected by the reduction in channel CaL, Ks, background calcium, and Kr. However, among the aforementioned major ion channels, only the CaL channel can play a superior role in prolonging the EMD up to 83 ms. Furthermore, ventricular cells with long EMD have been shown to inherit insignificant mechanical response (in terms of how strong the tension can grow and how far length shortening can go) compared with that in normal cells. In conclusion, despite all variations in every ion channel conductance, only the CaL channel can play a significant role in extending EMD. In addition, cardiac cells with long EMD tend to have inferior mechanical responses due to a lack of Cai compared with normal conditions, which are highly likely to result in a compromised pump function of the heart.