A large candidate gene survey identifies the KCNE1 D85N polymorphism as a possible modulator of drug-induced torsades de pointes

Pharmacogenomic markers associated with drug-induced QT prolongation: a systematic review

AIM

To systematically assess clinical studies involving patients undergoing drug therapy, comparing different genotypes to assess the relationship with changes in QT intervals, with no limitations on study design, setting, population, dosing regimens, or duration.

METHODS

This systematic review followed PRISMA guidelines and a pre-registered protocol. Clinical human studies on PGx markers of diQTP were identified, assessed using standardized tools, and categorized by design. Gene associations were classified as pharmacokinetic or pharmacodynamic. Identified genes underwent pathway enrichment analyses. Drugs were classified by third-level Anatomical Therapeutic Chemical (ATC) codes. Descriptive statistics were computed by study category and drug classes.

RESULTS

Of 4,493 reports, 84 studies were included, identifying 213 unique variants across 42 drug classes, of which 10% were replicated. KCNE1-Asp85Asn was the most consistent variant. Most findings (82%) were derived from candidate gene studies, suggesting bias toward known markers. The diQTP-associated genes were mainly linked to "cardiac conduction" and "muscle contraction" pathways (false discovery rate = 4.71 × 10-14). We also found an overlap between diQTP-associated genes and congenital long QT syndrome genes.

CONCLUSION

Key genes, drugs, and pathways were identified, but few consistent PGx markers emerged. Extensive, unbiased studies with diverse populations are crucial to advancing the field.

REGISTRATION

A protocol was pre-registered at PROSPERO under registration number CRD42022296097.

DATA DEPOSITION

Data sets generated by this review are available at figshare: DOI: 10.6084/m9.figshare.27959616.

High-throughput functional mapping of variants in an arrhythmia gene, KCNE1, reveals novel biology

BACKGROUND

KCNE1 encodes a 129-residue cardiac potassium channel (IKs) subunit. KCNE1 variants are associated with long QT syndrome and atrial fibrillation. However, most variants have insufficient evidence of clinical consequences and thus limited clinical utility.

METHODS

In this study, we leveraged the power of variant effect mapping, which couples saturation mutagenesis with high-throughput sequencing, to ascertain the function of thousands of protein-coding KCNE1 variants.

RESULTS

We comprehensively assayed KCNE1 variant cell surface expression (2554/2709 possible single-amino-acid variants) and function (2534 variants). Our study identified 470 loss- or partial loss-of-surface expression and 574 loss- or partial loss-of-function variants. Of the 574 loss- or partial loss-of-function variants, 152 (26.5%) had reduced cell surface expression, indicating that most functionally deleterious variants affect channel gating. Nonsense variants at residues 56-104 generally had WT-like trafficking scores but decreased functional scores, indicating that the latter half of the protein is dispensable for protein trafficking but essential for channel function. 22 of the 30 KCNE1 residues (73%) highly intolerant of variation (with > 70% loss-of-function variants) were in predicted close contact with binding partners KCNQ1 or calmodulin. Our functional assay data were consistent with gold standard electrophysiological data (ρ =  - 0.64), population and patient cohorts (32/38 presumed benign or pathogenic variants with consistent scores), and computational predictors (ρ =  - 0.62). Our data provide moderate-strength evidence for the American College of Medical Genetics/Association of Molecular Pathology functional criteria for benign and pathogenic variants.

CONCLUSIONS

Comprehensive variant effect maps of KCNE1 can both provide insight into I Ks channel biology and help reclassify variants of uncertain significance.

Escitalopram-induced QTc prolongation and its relationship with KCNQ1, KCNE1, and KCNH2 gene polymorphisms

BACKGROUND

Escitalopram can cause prolongation of the QT interval on the electrocardiogram (ECG). However, only some patients get pathological QTc prolongation in clinic. We investigated the influence of KCNQ1, KCNE1, and KCNH2 gene polymorphisms along with clinical factors on escitalopram-induced QTc prolongation.

METHODS

A total of 713 patients prescribed escitalopram were identified and had at least one ECG recording in this retrospective study. 472 patients with two or more ECG data were divided into QTc prolongation (n = 119) and non-prolongation (n = 353) groups depending on the threshold change in QTc of 30 ms above baseline value (∆QTc ≥ 30 ms). 45 patients in the QTc prolongation group and 90 patients in the QTc non-prolongation group were genotyped for 43 single nucleotide polymorphisms (SNPs) of KCNQ1, KCNE1, and KCNH2 genes.

RESULTS

Patients with QTc prolongation (∆QTc ≥ 30 ms) got higher escitalopram dose (10.3 mg) than patients without QTc prolongation (9.4 mg), although no significant relationship was found between QTc interval and escitalopram dose in the linear mixed model. Patients who were older/coronary disease/hypertension or carried with KCNE1 rs1805127 C allele, KCNE1 rs4817668 C allele, KCNH2 rs3807372 AG/GG genotype were significantly at risk for QTc prolongation (∆QTc ≥ 30 ms). Concomitant antipsychotic treatment was associated with a longer QTc interval.

LIMITATIONS

A relatively small sample size and lack of the blood concentration of escitalopram restricted the accurate relationship between escitalopram dose and QTc interval.

CONCLUSION

Our study revealed that KCNQ1, KCNE1, and KCNH2 gene polymorphisms along with clinical factors provide a complementary effect in escitalopram-induced QTc prolongation.

Genetic risk factors for drug-induced long QT syndrome: findings from a large real-world case-control study

Aim: Drug-induced long QT syndrome (diLQTS), an adverse effect of many drugs, can lead to sudden cardiac death. Candidate genetic variants in cardiac ion channels have been associated with diLQTS, but several limitations of previous studies hamper clinical utility. Materials & methods: Thus, the purpose of this study was to assess the associations of KCNE1-D85N, KCNE2-I57T and SCN5A-G615E with diLQTS in a large observational case-control study (6,083 self-reported white patients treated with 27 different high-risk QT-prolonging medications; 12.0% with diLQTS). Results: KCNE1-D85N significantly associated with diLQTS (adjusted odds ratio: 2.24 [95% CI: 1.35-3.58]; p = 0.001). Given low minor allele frequencies, the study had insufficient power to analyze KCNE2-I57T and SCN5A-G615E. Conclusion: KCNE1-D85N is a risk factor for diLQTS that should be considered in future clinical practice guidelines.

High-throughput functional mapping of variants in an arrhythmia gene, KCNE1, reveals novel biology

Background

KCNE1 encodes a 129-residue cardiac potassium channel (IKs) subunit. KCNE1 variants are associated with long QT syndrome and atrial fibrillation. However, most variants have insufficient evidence of clinical consequences and thus limited clinical utility.

Results

Here, we demonstrate the power of variant effect mapping, which couples saturation mutagenesis with high-throughput sequencing, to ascertain the function of thousands of protein coding KCNE1 variants. We comprehensively assayed KCNE1 variant cell surface expression (2,554/2,709 possible single amino acid variants) and function (2,539 variants). We identified 470 loss-of-surface expression and 588 loss-of-function variants. Out of the 588 loss-of-function variants, only 155 had low cell surface expression. The latter half of the protein is dispensable for protein trafficking but essential for channel function. 22 of the 30 KCNE1 residues (73%) highly intolerant of variation were in predicted close contact with binding partners KCNQ1 or calmodulin. Our data were highly concordant with gold standard electrophysiological data (ρ = -0.65), population and patient cohorts (32/38 concordant variants), and computational metrics (ρ = -0.55). Our data provide moderate-strength evidence for the ACMG/AMP functional criteria for benign and pathogenic variants.

Conclusions

Comprehensive variant effect maps of KCNE1 can both provide insight into IKs channel biology and help reclassify variants of uncertain significance.

The Advantages, Challenges, and Future of Human-Induced Pluripotent Stem Cell Lines in Type 2 Long QT Syndrome

Type 2 long QT syndrome (LQT2) is the second most common subtype of long QT syndrome and is caused by mutations in KCHN2 encoding the rapidly activating delayed rectifier potassium channel vital for ventricular repolarization. Sudden cardiac death is a sentinel event of LQT2. Preclinical diagnosis by genetic testing is potentially life-saving.Traditional LQT2 models cannot wholly recapitulate genetic and phenotypic features; therefore, there is a demand for a reliable experimental model. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) meet this challenge. This review introduces the advantages of the hiPSC-CM model over the traditional model and discusses how hiPSC-CM and gene editing are used to decipher mechanisms of LQT2, screen for cardiotoxicity, and identify therapeutic strategies, thus promoting the realization of precision medicine for LQT2 patients.

The impact of genetics on the long QT syndrome: myth or reality?

PURPOSE OF REVIEW

To summarize and critically assess the contribution of genetics to the Long QT Syndrome (LQTS), with specific reference to the unraveling of its underlying mechanisms and to its impact on clinical practice.

RECENT FINDINGS

The evolution towards our current approach to therapy for LQTS patients is examined in terms of risk stratification, gene-specific management, and assessment of the clinical impact that genetic modifiers may have in modulating the natural history of the patients. Glimpses are provided on the newest multidisciplinary approaches to study disease mechanisms, test new candidate drugs and identify precision treatments.

SUMMARY

It is undeniable that genetics has revolutionized our mechanistic understanding of cardiac channelopathies. Its impact has been enormous but, curiously, the way LQTS patients are being treated today is largely the same that was used in the pregenetic era, even though management has been refined and gene-specific differences allow a more individually tailored antiarrhythmic protection. The synergy of genetic findings with modern in vitro and in silico tools may expand precision treatments; however, they will need to prove more effective than the current therapeutic approaches and equally safe.

Cardiac Repolarization in Health and Disease

Abnormal cardiac repolarization is at the basis of life-threatening arrhythmias in various congenital and acquired cardiac diseases. Dysfunction of ion channels involved in repolarization at the cellular level are often the underlying cause of the repolarization abnormality. The expression pattern of the gene encoding the affected ion channel dictates its impact on the shape of the T-wave and duration of the QT interval, thereby setting the stage for both the occurrence of the trigger and the substrate for maintenance of the arrhythmia. Here we discuss how research into the genetic and electrophysiological basis of repolarization has provided us with insights into cardiac repolarization in health and disease and how this in turn may provide the basis for future improved patient-specific management.

Curcumin, a dietary natural supplement, prolongs the action potential duration of KCNE1-D85N-induced pluripotent stem cell-derived cardiomyocytes

BACKGROUND

Curcumin, a polyphenolic dietary natural compound and active ingredient in turmeric, exerts antioxidant, anti-inflammatory, antidiabetic, anticancer, and antiarrhythmic properties. KCNE1-D85N, present in ∼1% of white, is a common, potentially proarrhythmic variant that predisposes individuals to drug-induced QT prolongation under certain conditions.

OBJECTIVE

The purpose of this article was to test the hypothesis that curcumin might cause action potential duration (APD) prolongation in KCNE1-D85N-derived human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs).

METHODS

Gene-edited/variant-corrected isogenic control and patient-specific KCNE1-D85N-containing iPSC-CMs were generated previously. Voltage-sensing dye, multielectrode array (MEA), and whole-cell patch clamp technique were used to measure APD without and with 4-hour incubation with 10 nM curcumin.

RESULTS

KCNE1-D85N-derived iPSC-CMs demonstrated significant APD prolongation with treatment of 10 nM curcumin. Using voltage-sensing dye, action potential duration at 90% repolarization (APD90) was 578 ± 7 ms (n = 39) at baseline and was prolonged to 658 ± 13 ms (n = 35) with curcumin incubation (P < .0001). Using MEA, APD90 at baseline was 237 ± 6 ms (n = 24) compared with 280 ± 6 ms (n = 12) with curcumin incubation (P = .0002). The whole-cell patch clamp technique confirmed these results, with APD90 being 544 ± 37 ms at baseline and 664 ± 40 ms with treatment of curcumin (P < .005). However, APD from isogenic control iPSC-CMs remained unchanged with curcumin treatment.

CONCLUSION

This study provides pharmacological and functional evidence to suggest that curcumin, a dietary natural supplement, might cause APD prolongation in patients with common, potentially proarrhythmic functional variants such as KCNE1-D85N. Whether this supplement is potentially dangerous for the Caucasian subpopulation that has this variant warrants further investigation.

The genetics of drug-induced QT prolongation: evaluating the evidence for pharmacodynamic variants

Drug-induced long QT syndrome (diLQTS) is an adverse effect of many commonly prescribed drugs, and it can increase the risk for lethal ventricular arrhythmias. Genetic variants in pharmacodynamic genes have been associated with diLQTS, but the strength of the evidence for each of those variants has not yet been evaluated. Therefore, the purpose of this review was to evaluate the strength of the evidence for pharmacodynamic genetic variants associated with diLQTS using a novel, semiquantitative scoring system modified from the approach used for congenital LQTS. KCNE1-D85N and KCNE2-T8A had definitive and strong evidence for diLQTS, respectively. The high level of evidence for these variants supports current consideration as risk factors for patients that will be prescribed a QT-prolonging drug.

Rare Variation in Drug Metabolism and Long QT Genes and the Genetic Susceptibility to Acquired Long QT Syndrome

BACKGROUND

Acquired long QT syndrome (aLQTS) is a serious unpredictable adverse drug reaction. Pharmacogenomic markers may predict risk.

METHODS

Among 153 aLQTS patients (mean age 58 years [range, 14-88], 98.7% White, 85.6% symptomatic), computational methods identified proteins interacting most significantly with 216 QT-prolonging drugs. All cases underwent sequencing of 31 candidate genes arising from this analysis or associating with congenital LQTS. Variants were filtered using a minor allele frequency <1% and classified for susceptibility for aLQTS. Gene-burden analyses were then performed comparing the primary cohort to control exomes (n=452) and an independent replication aLQTS exome sequencing cohort.

RESULTS

In 25.5% of cases, at least one rare variant was identified: 22.2% of cases carried a rare variant in a gene associated with congenital LQTS, and in 4% of cases that variant was known to be pathogenic or likely pathogenic for congenital LQTS; 7.8% cases carried a cytochrome-P450 (CYP) gene variant. Of 12 identified CYP variants, 11 (92%) were in an enzyme known to metabolize at least one culprit drug to which the subject had been exposed. Drug-drug interactions that affected culprit drug metabolism were found in 19% of cases. More than one congenital LQTS variant, CYP gene variant, or drug interaction was present in 7.8% of cases. Gene-burden analyses of the primary cohort compared to control exomes (n=452), and an independent replication aLQTS exome sequencing cohort (n=67) and drug-tolerant controls (n=148) demonstrated an increased burden of rare (minor allele frequency<0.01) variants in CYP genes but not LQTS genes.

CONCLUSIONS

Rare susceptibility variants in CYP genes are emerging as potentially important pharmacogenomic risk markers for aLQTS and could form part of personalized medicine approaches in the future.

Common Ancestry-Specific Ion Channel Variants Predispose to Drug-Induced Arrhythmias

BACKGROUND

Multiple reports associate the cardiac sodium channel gene (SCN5A) variants S1103Y and R1193Q with type 3 congenital long QT syndrome and drug-induced long QT syndrome. These variants are too common in ancestral populations to be highly arrhythmogenic at baseline, however: S1103Y allele frequency is 8.1% in African Americans and R1193Q 6.1% in East Asians. R1193Q is known to increase late sodium current (I_Na-L) in cardiomyocytes derived from induced pluripotent stem cells but the role of these variants in modulating repolarization remains poorly understood.

METHODS

We determined the effect of S1103Y on QT intervals among African-American participants in a large electronic health record. Using cardiomyocytes derived from induced pluripotent stem cells carrying naturally occurring or genome-edited variants, we studied action potential durations (APDs) at baseline and after challenge with the repolarizing potassium current (I_Kr) blocker dofetilide and I_Na-L and I_Kr at baseline.

RESULTS

In 1479 African-American participants with no confounding medications or diagnoses of heart disease, QT intervals in S1103Y carriers was no different from that in noncarriers. Baseline APD was no different in cells expressing the Y allele (SY, YY cells) compared with isogenic cells with the reference allele (SS cells). However, I_Na-L was increased in SY and YY cells and the I_Na-L blocker GS967 shortened APD in SY/YY but not SS cells (P<0.001). I_Kr was increased almost 2-fold in SY/YY cells compared with SS cells (tail current: 0.66±0.1 versus 1.2±0.1 pA/pF; P<0.001). Dofetilide challenge prolonged APD at much lower concentrations in SY (4.1 nmol/L [interquartile range, 1.5-9.3]; n=11) and YY (4.2 nmol/L [1.7-5.0]; n=5) than in SS cells (249 nmol/L [22.3-2905]; n=14; P<0.001 and P<0.01, respectively) and elicited afterdepolarizations in 8/16 SY/YY cells but only in 1/14 SS cells. R1193Q cells similarly displayed no difference in baseline APD but increased I_Kr and increased dofetilide sensitivity.

CONCLUSIONS

These common ancestry-specific variants do not affect baseline repolarization, despite generating increased I_Na-L. We propose that increased I_Kr serves to maintain normal repolarization but increases the risk of manifest QT prolongation with I_Kr block in variant carriers. Our findings emphasize the need for inclusion of diverse populations in the study of adverse drug reactions.

Clinical Genetics of Inherited Arrhythmogenic Disease in the Pediatric Population

Sudden death is a rare event in the pediatric population but with a social shock due to its presentation as the first symptom in previously healthy children. Comprehensive autopsy in pediatric cases identify an inconclusive cause in 40-50% of cases. In such cases, a diagnosis of sudden arrhythmic death syndrome is suggested as the main potential cause of death. Molecular autopsy identifies nearly 30% of cases under 16 years of age carrying a pathogenic/potentially pathogenic alteration in genes associated with any inherited arrhythmogenic disease. In the last few years, despite the increasing rate of post-mortem genetic diagnosis, many families still remain without a conclusive genetic cause of the unexpected death. Current challenges in genetic diagnosis are the establishment of a correct genotype-phenotype association between genes and inherited arrhythmogenic disease, as well as the classification of variants of uncertain significance. In this review, we provide an update on the state of the art in the genetic diagnosis of inherited arrhythmogenic disease in the pediatric population. We focus on emerging publications on gene curation for genotype-phenotype associations, cases of genetic overlap and advances in the classification of variants of uncertain significance. Our goal is to facilitate the translation of genetic diagnosis to the clinical area, helping risk stratification, treatment and the genetic counselling of families.

Genetics and genomics of arrhythmic risk: current and future strategies to prevent sudden cardiac death

A genetic risk of sudden cardiac arrest and sudden death due to an arrhythmic cause, known as sudden cardiac death (SCD), has become apparent from epidemiological studies in the general population and in patients with ischaemic heart disease. However, genetic susceptibility to sudden death is greatest in young people and is associated with uncommon, monogenic forms of heart disease. Despite comprehensive pathology and genetic evaluations, SCD remains unexplained in a proportion of young people and is termed sudden arrhythmic death syndrome, which poses challenges to the identification of relatives from affected families who might be at risk of SCD. In this Review, we assess the current understanding of the epidemiology and causes of SCD and evaluate both the monogenic and the polygenic contributions to the risk of SCD in the young and SCD associated with drug therapy. Finally, we analyse the potential clinical role of genomic testing in the prevention of SCD in the general population.

Anti-Ro/SSA Antibodies and the Autoimmune Long-QT Syndrome

Autoimmunity is increasingly recognized as a novel pathogenic mechanism for cardiac arrhythmias. Several arrhythmogenic autoantibodies have been identified, cross-reacting with different types of surface proteins critically involved in the cardiomyocyte electrophysiology, primarily ion channels (autoimmune cardiac channelopathies). Specifically, some of these autoantibodies can prolong the action potential duration leading to acquired long-QT syndrome (LQTS), a condition known to increase the risk of life-threatening ventricular arrhythmias, particularly Torsades de Pointes (TdP). The most investigated form of autoimmune LQTS is associated with the presence of circulating anti-Ro/SSA-antibodies, frequently found in patients with autoimmune diseases (AD), but also in a significant proportion of apparently healthy subjects of the general population. Accumulating evidence indicates that anti-Ro/SSA-antibodies can markedly delay the ventricular repolarization via a direct inhibitory cross-reaction with the extracellular pore region of the human-ether-a-go-go-related (hERG) potassium channel, resulting in a higher propensity for anti-Ro/SSA-positive subjects to develop LQTS and ventricular arrhythmias/TdP. Recent population data demonstrate that the risk of LQTS in subjects with circulating anti-Ro/SSA antibodies is significantly increased independent of a history of overt AD, intriguingly suggesting that these autoantibodies may silently contribute to a number of cases of ventricular arrhythmias and cardiac arrest in the general population. In this review, we highlight the current knowledge in this topic providing complementary basic, clinical and population health perspectives.

Out-of-hospital cardiac arrest and differential risk of cardiac and non-cardiac QT-prolonging drugs in 37 000 cases

Aims

Drugs that prolong the QT interval, either by design (cardiac QT‐prolonging drugs: anti‐arrhythmics) or as off‐target effect (non‐cardiac QT‐prolonging drugs), may increase the risk of ventricular arrhythmias and out‐of‐hospital cardiac arrest (OHCA). Risk mitigation measures were instituted, in particular, surrounding prescription of cardiac QT‐prolonging drugs. We studied OHCA risk of both drug types in current clinical practice.

Methods

Using data from large population‐based OHCA registries in the Netherlands and Denmark, we conducted two independent case–control studies. OHCA cases with presumed cardiac causes were matched on age/sex/index date with up to five non‐OHCA controls. We calculated odds ratios (ORs) for the association of cardiac or non‐cardiac QT‐prolonging drugs with OHCA risk using conditional logistic regression analyses.

Results

We identified 2503 OHCA cases and 10 543 non‐OHCA controls in the Netherlands, and 35 017 OHCA cases and 175 085 non‐OHCA controls in Denmark. Compared to no use of QT‐prolonging drugs, use of non‐cardiac QT‐prolonging drugs (Netherlands: cases: 3.0%, controls: 1.9%; Denmark: cases: 14.9%, controls: 7.5%) was associated with increased OHCA risk (Netherlands: OR 1.37 [95% CI: 1.03–1.81]; Denmark: OR 1.63 [95% CI: 1.57–1.70]). The association between cardiac QT‐prolonging drugs (Netherlands: cases: 4.0%, controls: 2.5%; Denmark: cases: 2.1%, controls: 0.9%) and OHCA was weaker (Netherlands: OR 1.17 [95% CI: 0.92–1.50]; Denmark: OR 1.21 [95% CI: 1.09–1.33]), although users of cardiac QT‐prolonging drugs had more medication use and comorbidities associated with OHCA risk than users of non‐cardiac QT‐prolonging drugs.

Conclusion

In clinical practice, cardiac QT‐prolonging drugs confer lower OHCA risk than non‐cardiac QT‐prolonging drugs, although users of the former have higher a priori risk. This is likely due to risk mitigation measures surrounding prescription of cardiac QT‐prolonging drugs.

Development of a Patient-Specific p.D85N-Potassium Voltage-Gated Channel Subfamily E Member 1-Induced Pluripotent Stem Cell-Derived Cardiomyocyte Model for Drug-Induced Long QT Syndrome

BACKGROUND

Prior epidemiological studies demonstrated that the p.D85N-Potassium voltage-gated channel subfamily E member 1 (KCNE1) common variant reduces repolarization reserve and predisposes to drug-induced QT prolongation/torsades de pointes. We sought to develop a cellular model for drug-induced long QT syndrome using a patient-specific induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM).

METHODS

p.D85N-KCNE1 iPSCs were generated from a 23-year-old female with an exaggerated heart rate-corrected QT interval response to metoclopramide (ΔQTc of 160 ms). Clustered regularly interspaced short palindromic repeats-associated 9 technology was used to generate gene-corrected isogenic iPSCs. Field potential duration and action potential duration (APD) were measured from iPSC-CMs.

RESULTS

At baseline, p.D85N-KCNE1 iPSC-CMs displayed significantly longer field potential duration (281±15 ms, n=13 versus 223±8.6 ms, n=14, P<0.01) and action potential duration at 90% repolarization (APD90; 579±22 ms, n=24 versus 465±33 ms, n=26, P<0.01) than isogenic-control iPSC-CMs. Dofetilide at a concentration of 2 nM increased significantly field potential duration (379±20 ms, n=13, P<0.01) and APD90 (666±11 ms, n=46, P<0.01) in p.D85N-KCNE1 iPSC-CMs but not in isogenic-control. The effect of dofetilide on APD90 (616±54 ms, n=7 versus 526±54 ms, n=10, P<0.05) was confirmed by Patch-clamp. Interestingly, treatment of p.D85N-KCNE1 iPSC-CMs with estrogen at a concentration of 1 nM exaggerated further dofetilide-induced APD90 prolongation (696±9 ms, n=81, P<0.01) and caused more early afterdepolarizations (11.7%) compared with isogenic control (APD90: 618±8 ms, n=115 and early afterdepolarizations: 2.6%, P<0.05).

CONCLUSIONS

This iPSC-CM study provides further evidence that the p.D85N-KCNE1 common variant in combination with environmental factors such as QT prolonging drugs and female sex is proarrhythmic.

Variant Reinterpretation in Survivors of Cardiac Arrest With Preserved Ejection Fraction (the Cardiac Arrest Survivors With Preserved Ejection Fraction Registry) by Clinicians and Clinical Commercial Laboratories

BACKGROUND

Following an unexplained cardiac arrest, clinical genetic testing is increasingly becoming standard of care. Periodic review of variant classification is required, as reinterpretation can change the diagnosis, prognosis, and management of patients and their relatives.

METHODS

This study aimed to develop and validate a standardized algorithm to facilitate clinical application of the 2015 American College of Medical Genetics and Association for Molecular Pathology guidelines for the interpretation of genetic variants. The algorithm was applied to genetic results in the Cardiac Arrest Survivors With Preserved Ejection Fraction Registry, to assess the rate of variant reclassification over time. Variant classifications were then compared with the classifications of 2 commercial laboratories to determine the rate and identify sources of variant interpretation discordance.

RESULTS

Thirty-one percent of participants (40 of 131) had at least 1 genetic variant with a clinically significant reclassification over time. Variants of uncertain significance were more likely to be downgraded (73%) to benign than upgraded to pathogenic (27%; P=0.03). For the second part of the study, 50% (70 of 139) of variants had discrepant interpretations (excluding benign variants), provided by at least 1 team.

CONCLUSIONS

Periodic review of genetic variant classification is a key component of follow-up care given rapidly changing information in the field. There is potential for clinical care gaps with discrepant variant interpretations, based on the interpretation and application of current guidelines. The development of gene- and disease-specific guidelines and algorithms may provide an opportunity to further standardize variant interpretation reporting in the future. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT00292032.

Elevation of propofol sensitivity of cardiac IKs channel by KCNE1 polymorphism D85N

BACKGROUND AND PURPOSE

The slowly activating delayed rectifier K⁺ channel (I_Ks ), composed of pore-forming KCNQ1 α-subunits and ancillary KCNE1 β-subunits, regulates ventricular repolarization in human heart. Propofol, at clinically used concentrations, modestly inhibits the intact (wild-type) I_Ks channels and is therefore unlikely to appreciably prolong QT interval in ECG during anaesthesia. However, little information is available concerning the inhibitory effect of propofol on I_Ks channel associated with its gene variants implicated in QT prolongation. The KCNE1 single nucleotide polymorphism leading to D85N is associated with drug-induced QT prolongation and therefore regarded as a clinically important genetic variant. This study examined whether KCNE1-D85N affects the sensitivity of I_Ks to inhibition by propofol.

EXPERIMENTAL APPROACH

Whole-cell patch-clamp and immunostaining experiments were conducted in HEK293 cells and/or mouse cardiomyocyte-derived HL-1 cells, transfected with wild-type KCNQ1, wild-type or variant KCNE1 cDNAs.

KEY RESULTS

Propofol inhibited KCNQ1/KCNE1-D85N current more potently than KCNQ1/KCNE1 current in HEK293 cells and HL-1 cells. Immunostaining experiments in HEK293 cells revealed that pretreatment with propofol (10 μM) did not appreciably affect cell membrane expression of KCNQ1 and KCNE1 proteins in KCNQ1/KCNE1 and KCNQ1/KCNE1-D85N channels.

CONCLUSION AND IMPLICATIONS

The KCNE1 polymorphism D85N significantly elevates the sensitivity of I_Ks to inhibition by propofol. This study detects a functionally important role of KCNE1-D85N polymorphism in conferring genetic susceptibility to propofol-induced QT prolongation and further suggests the possibility that the inhibitory action of anaesthetics on ionic currents becomes exaggerated in patients carrying variants in genes encoding ion channels.

European Resuscitation Council Guidelines 2021: Epidemiology of cardiac arrest in Europe

In this section of the European Resuscitation Council Guidelines 2021, key information on the epidemiology and outcome of in and out of hospital cardiac arrest are presented. Key contributions from the European Registry of Cardiac Arrest (EuReCa) collaboration are highlighted. Recommendations are presented to enable health systems to develop registries as a platform for quality improvement and to inform health system planning and responses to cardiac arrest.

The Role of Pharmacogenomics in Contemporary Cardiovascular Therapy: A position statement from the European Society of Cardiology Working Group on Cardiovascular Pharmacotherapy

There is a strong and ever-growing body of evidence regarding the use of pharmacogenomics to inform cardiovascular pharmacology. However, there is no common position taken by international cardiovascular societies to unite diverse availability, interpretation and application of such data, nor is there recognition of the challenges of variation in clinical practice between countries within Europe. Aside from the considerable barriers to implementing pharmacogenomic testing and the complexities of clinically actioning results, there are differences in the availability of resources and expertise internationally within Europe. Diverse legal and ethical approaches to genomic testing and clinical therapeutic application also require serious thought. As direct-to-consumer genomic testing becomes more common, it can be anticipated that data may be brought in by patients themselves, which will require critical assessment by the clinical cardiovascular prescriber. In a modern, pluralistic and multi-ethnic Europe, self-identified race/ethnicity may not be concordant with genetically detected ancestry and thus may not accurately convey polymorphism prevalence. Given the broad relevance of pharmacogenomics to areas such as thrombosis and coagulation, interventional cardiology, heart failure, arrhythmias, clinical trials, and policy/regulatory activity within cardiovascular medicine, as well as to genomic and pharmacology subspecialists, this position statement attempts to address these issues at a wide-ranging level.

Sex-specific IKAS activation in rabbit ventricles with drug-induced QT prolongation

BACKGROUND

Female sex is a known risk factor for drug-induced long QT syndrome (diLQTS). We recently demonstrated a sex difference in apamin-sensitive small-conductance Ca2+-activated K+ current (IKAS) activation during β-adrenergic stimulation.

OBJECTIVE

The purpose of this study was to test the hypothesis that there is a sex difference in IKAS in the rabbit models of diLQTS.

METHODS

We evaluated the sex difference in ventricular repolarization in 15 male and 22 female Langendorff-perfused rabbit hearts with optical mapping techniques during atrial pacing. HMR1556 (slowly activating delayed rectifier K+ current [IKs] blocker), E4031 (rapidly activating delayed rectifier K+ current [IKr] blocker) and sea anemone toxin (ATX-II, late Na+ current [INaL] activator) were used to simulate types 1-3 long QT syndrome, respectively. Apamin, an IKAS blocker, was then added to determine the magnitude of further QT prolongation.

RESULTS

HMR1556, E4031, and ATX-II led to the prolongation of action potential duration at 80% repolarization (APD80) in both male and female ventricles at pacing cycle lengths of 300-400 ms. Apamin further prolonged APD80 (pacing cycle length 350 ms) from 187.8±4.3 to 206.9±7.1 (P=.014) in HMR1556-treated, from 209.9±7.8 to 224.9±7.8 (P=.003) in E4031-treated, and from 174.3±3.3 to 188.1±3.0 (P=.0002) in ATX-II-treated female hearts. Apamin did not further prolong the APD80 in male hearts. The Cai transient duration (CaiTD) was significantly longer in diLQTS than baseline but without sex differences. Apamin did not change CaiTD.

CONCLUSION

We conclude that IKAS is abundantly increased in female but not in male ventricles with diLQTS. Increased IKAS helps preserve the repolarization reserve in female ventricles treated with IKs and IKr blockers or INaL activators.

Prophylactic (hydroxy)chloroquine in COVID-19: Potential relevance for cardiac arrhythmia risk

(Hydroxy)chloroquine ((H)CQ) is being investigated as a treatment for COVID-19, but studies have so far demonstrated either no or a small benefit. However, these studies have been mostly performed in patients admitted to the hospital and hence likely already (severely) affected. Another suggested approach uses prophylactic (H)CQ treatment aimed at preventing either severe acute respiratory syndrome coronavirus 2 infection or the development of disease. A substantial number of clinical trials are planned or underway aimed at assessing the prophylactic benefit of (H)CQ. However, (H)CQ may lead to QT prolongation and potentially induce life-threatening arrhythmias. This may be of particular relevance to patients with preexisting cardiovascular disease and those taking other QT-prolonging drugs. In addition, it is known that a certain percentage of the population carries genetic variant(s) that reduces their repolarization reserve, predisposing them to (H)CQ-induced QT prolongation, and this may be more relevant to female patients who already have a longer QT interval to start with. This review provides an overview of the current evidence on (H)CQ therapy in patients with COVID-19 and discusses different strategies for prophylactic (H)CQ therapy (ie, preinfection, postexposure, and postinfection). In particular, the potential cardiac effects, including QT prolongation and arrhythmias, will be addressed. Based on these insights, recommendations will be presented as to which preventive measures should be taken when giving (H)CQ prophylactically, including electrocardiographic monitoring.

Transethnic Genome-Wide Association Study Provides Insights in the Genetic Architecture and Heritability of Long QT Syndrome

BACKGROUND

Long QT syndrome (LQTS) is a rare genetic disorder and a major preventable cause of sudden cardiac death in the young. A causal rare genetic variant with large effect size is identified in up to 80% of probands (genotype positive) and cascade family screening shows incomplete penetrance of genetic variants. Furthermore, a proportion of cases meeting diagnostic criteria for LQTS remain genetically elusive despite genetic testing of established genes (genotype negative). These observations raise the possibility that common genetic variants with small effect size contribute to the clinical picture of LQTS. This study aimed to characterize and quantify the contribution of common genetic variation to LQTS disease susceptibility.

METHODS

We conducted genome-wide association studies followed by transethnic meta-analysis in 1656 unrelated patients with LQTS of European or Japanese ancestry and 9890 controls to identify susceptibility single nucleotide polymorphisms. We estimated the common variant heritability of LQTS and tested the genetic correlation between LQTS susceptibility and other cardiac traits. Furthermore, we tested the aggregate effect of the 68 single nucleotide polymorphisms previously associated with the QT-interval in the general population using a polygenic risk score.

RESULTS

Genome-wide association analysis identified 3 loci associated with LQTS at genome-wide statistical significance (P<5×10-8) near NOS1AP, KCNQ1, and KLF12, and 1 missense variant in KCNE1(p.Asp85Asn) at the suggestive threshold (P<10-6). Heritability analyses showed that ≈15% of variance in overall LQTS susceptibility was attributable to common genetic variation (h2SNP 0.148; standard error 0.019). LQTS susceptibility showed a strong genome-wide genetic correlation with the QT-interval in the general population (rg=0.40; P=3.2×10-3). The polygenic risk score comprising common variants previously associated with the QT-interval in the general population was greater in LQTS cases compared with controls (P<10-13), and it is notable that, among patients with LQTS, this polygenic risk score was greater in patients who were genotype negative compared with those who were genotype positive (P<0.005).

CONCLUSIONS

This work establishes an important role for common genetic variation in susceptibility to LQTS. We demonstrate overlap between genetic control of the QT-interval in the general population and genetic factors contributing to LQTS susceptibility. Using polygenic risk score analyses aggregating common genetic variants that modulate the QT-interval in the general population, we provide evidence for a polygenic architecture in genotype negative LQTS.

Hydroxychloroquine in COVID-19 Therapy: Protection Versus Proarrhythmia

In recent months, the new coronavirus SARS-CoV-2 has emerged as a worldwide threat with about 4.2 million confirmed cases and almost 300 000 deaths. Its major clinical presentation is characterized by respiratory symptoms ranging from mild cough to serve pneumonia with fever and potentially even death. Until today, there is no known medication to improve clinical symptoms or even prevent or fight the infection. The search for a useful vaccination is ongoing and it will probably not be available before the end of 2020. In this review, we highlight hydroxychloroquine (HCQ) as a potential agent to prevent coronavirus disease 2019 (COVID-19) and reduce as well as shorten clinical symptoms. Moreover, it might serve as a potential post-exposition prophylaxis. Although it has been used in the treatment of rheumatoid arthritis, discoid or systemic lupus erythematosus, and malaria prophylaxis and therapy for decades, knowledge on HCQ as a potential treatment for COVID-19 is limited and multiple clinical trials have just emerged. Especially, rare HCQ side effects which were of minor importance for use in selected indications might gain major relevance with population-wide application. These rare side effects include retinopathy and-even more important-QT prolongation leading to sudden cardiac death by malignant arrhythmias.

A current understanding of drug-induced QT prolongation and its implications for anticancer therapy

The QT interval, a global index of ventricular repolarization, varies among individuals and is influenced by diverse physiologic and pathophysiologic stimuli such as gender, age, heart rate, electrolyte concentrations, concomitant cardiac disease, and other diseases such as diabetes. Many drugs produce a small but reproducible effect on QT interval but in rare instances this is exaggerated and marked QT prolongation can provoke the polymorphic ventricular tachycardia 'torsades de pointes', which can cause syncope or sudden cardiac death. The generally accepted common mechanism whereby drugs prolong QT is block of a key repolarizing potassium current in heart, IKr, generated by expression of KCNH2, also known as HERG. Thus, evaluation of the potential that a new drug entity may cause torsades de pointes has relied on exposure of normal volunteers or patients to drug at usual and high concentrations, and on assessment of IKr block in vitro. More recent work, focusing on anticancer drugs with QT prolonging liability, is defining new pathways whereby drugs can prolong QT. Notably, the in vitro effects of some tyrosine kinase inhibitors to prolong cardiac action potentials (the cellular correlate of QT) can be rescued by intracellular phosphatidylinositol 3,4,5-trisphosphate, the downstream effector of phosphoinositide 3-kinase. This finding supports a role for inhibition of this enzyme, either directly or by inhibition of upstream kinases, to prolong QT through mechanisms that are being worked out, but include enhanced inward 'late' sodium current during the plateau of the action potential. The definition of non-IKr-dependent pathways to QT prolongation will be important for assessing risk, not only with anticancer therapies but also with other QT prolonging drugs and for generating a refined understanding how variable activity of intracellular signalling systems can modulate QT and associated arrhythmia risk.

Explaining sudden infant death with cardiac arrhythmias: Complete exon sequencing of nine cardiac arrhythmia genes in Dutch SIDS cases highlights new and known DNA variants

Previous studies suggested that Sudden Infant Death Syndrome (SIDS) can partially be genetically explained by cardiac arrhythmias; however, the number of individuals and populations investigated remain limited. We report the first SIDS study on cardiac arrhythmias genes from the Netherlands, a country with the lowest SIDS incidence likely due to parent education on awareness of environmental risk factors. By using targeted massively parallel sequencing (MPS) in 142 Dutch SIDS cases, we performed a complete exon screening of all 173 exons from 9 cardiac arrhythmias genes SCN5A, KCNQ1, KCNH2, KCNE1, KCNE2, CACNA1C, CAV3, ANK2 and KCNJ2 (∼34,000 base pairs), that were selected to harbour previously established SIDS-associated DNA variants. Motivated by the poor DNA quality from the paraffin embedded material used, the application of a conservative sequencing quality control protocol resulted in 102 SIDS cases surviving quality control. Amongst the 102 SIDS cases, we identified a total of 40 DNA variants in 8 cardiac arrhythmia genes found in 60 (58.8 %) cases. Statistical analyses using ancestry-adjusted reference population data and multiple test correction revealed that 13 (32.5 %) of the identified DNA variants in 6 cardiac arrhythmia genes were significantly associated with SIDS, which were observed in 15 (14.7 %) SIDS cases. These 13, and another three, DNA variants were classified as likely pathogenic for cardiac arrhythmias using the American College of Medical Genetics guidelines for interpretation of sequence variants. The 16 likely pathogenic DNA variants were found in 16 (15.7 %) SIDS cases, including i) 3 novel DNA variants not recorded in public databases ii) 7 known DNA variants for which significant SIDS association established here was previously unknown, and iii) 6 known DNA variants for which LQTS association was reported previously. By having replicated previously reported SIDS-associated DNA variants located in cardiac arrhythmia genes and by having highlighting novel SIDS-associated DNA variants in such genes, our findings provide additional empirical evidence for the partial genetic explanation of SIDS by cardiac arrhythmias. On a wider note, our study outcome stresses the need for routine post-mortem genetic screening of assumed SIDS cases, particularly for cardiac arrhythmia genes. When put in practise, it will allow preventing further sudden deaths (not only in infants) in the affected families, thereby allowing forensic molecular autopsy not only to provide answers on the cause of death, but moreover to save lives.

Clinical and functional reappraisal of alleged type 5 long QT syndrome: Causative genetic variants in the KCNE1-encoded minK β-subunit

BACKGROUND

KCNE1 loss-of-function variants cause type 5 long QT syndrome (LQT5). However, most alleged LQT5-causative KCNE1 variants were identified before the true rate of background genetic variation was appreciated fully.

OBJECTIVE

The purpose of this study was to reassess the clinical and electrophysiological (EP) phenotypes associated with KCNE1 variants detected in a single-center LQTS cohort.

METHODS

Retrospective analysis of 1026 LQTS patients was used to identify those individuals with isolated KCNE1 ultra-rare variants (minor allele frequency [MAF] <0.0004 in the Genome Aggregation Database [gnomAD]). After classification according to American College of Medical Genetics (ACMG) guidelines, variants of uncertain significance (VUS) were characterized in vitro using whole-cell patch-clamp technique. Lastly, the clinical phenotype observed in ACMG pathogenic/likely pathogenic (P/LP) KCNE1-positive individuals was assessed.

RESULTS

Overall, 6 KCNE1 variants were identified in 38 of 1026 LQTS patients (3.7%). Based on existing data, 2 KCNE1 variants (p.Asp76Asn-KCNE1 and p.Arg98Trp-KCNE1) were classified as P/LP. Whereas the p.Ser28Leu-KCNE1 VUS conferred a loss-of-function EP phenotype (72% reduction in I_Ks current) and was upgraded to an LP variant, the 3 remaining KCNE1 VUS (p.Arg67Cys-KCNE1, p.Arg67His-KCNE1, p.Ser74Leu-KCNE1) were indistinguishable from wild type. Collectively, the phenotype observed in p.Ser28Leu-KCNE1-, p.Asp76Asn-KCNE1-, and p.Arg98Trp-KCNE1-positive individuals (n = 22) was relatively weak (91% asymptomatic; average QTc 444 ± 19 ms; 27% with a maladaptive QTc response during exercise/recovery).

CONCLUSION

This study indicates that p.Ser28Leu-KCNE1 may be an LQT5-causative substrate analogous to p.Asp76Asn-KCNE1 and p.Arg98Trp-KCNE1. However, the weak phenotype and cumulative gnomAD MAF (42/141,156) associated with these P/LP variants suggest LQT5/KCNE-LQTS may be a more common/weaker form of LQTS than anticipated previously.

QTc Prolongation and Risk of Torsades de Pointes in Hospitalized Pediatric Oncology Patients

OBJECTIVE

To evaluate the prevalence of torsades de pointes and to identify risk factors associated with QTc prolongation of ≥500 milliseconds in hospitalized pediatric oncology patients. A QTc prolongation of ≥500 milliseconds is associated with higher mortality in hospitalized adults but has not been demonstrated in pediatrics.

STUDY DESIGN

A single-center, retrospective review of all hospitalized oncology patients ≤21 years of age was performed from 2014 to 2016. Patients with long/short QT syndrome or a QRS interval of ≥120 ms were excluded. Rapid response events were reviewed to determine the prevalence of torsades. In patients with ECGs for review, data were compared between patients with a QTc of <500 and ≥500 ms via logistic regression.

RESULTS

There were 1934 hospitalized patients included. Rapid response events occurred in 90 patients (4.7%) with 2 torsades events (0.1%). There were 1412 electrocardiograms performed in 287 unique patients (10.6 ± 6.3 years of age; 43% female). The mean QTc was 448 ± 31 ms; 25 patients (8.7%) had ≥1 ECG with a QTc of ≥500 ms. The prevalence of torsades was greater in patients with a QTc of ≥500 ms (8% vs 0%; P<.01). In multivariate analysis, factors associated with a QTc of ≥500 ms included female sex, (OR 2.95) and ≥2 QT-prolonging medications (OR, 2.95).

CONCLUSIONS

The prevalence of torsades in hospitalized pediatric oncology patients was low (0.1%), although the risk was significantly greater in patients with a QTc of ≥500 ms. Routine monitoring of electrocardiograms and electrolytes is essential in patients with risk factors predisposing to QTc prolongation.

An International, Multicentered, Evidence-Based Reappraisal of Genes Reported to Cause Congenital Long QT Syndrome

Supplemental Digital Content is available in the text.

Background:

Long QT syndrome (LQTS) is the first described and most common inherited arrhythmia. Over the last 25 years, multiple genes have been reported to cause this condition and are routinely tested in patients. Because of dramatic changes in our understanding of human genetic variation, reappraisal of reported genetic causes for LQTS is required.

Methods:

Utilizing an evidence-based framework, 3 gene curation teams blinded to each other’s work scored the level of evidence for 17 genes reported to cause LQTS. A Clinical Domain Channelopathy Working Group provided a final classification of these genes for causation of LQTS after assessment of the evidence scored by the independent curation teams.

Results:

Of 17 genes reported as being causative for LQTS, 9 (AKAP9, ANK2, CAV3, KCNE1, KCNE2, KCNJ2, KCNJ5, SCN4B, SNTA1) were classified as having limited or disputed evidence as LQTS-causative genes. Only 3 genes (KCNQ1, KCNH2, SCN5A) were curated as definitive genes for typical LQTS. Another 4 genes (CALM1, CALM2, CALM3, TRDN) were found to have strong or definitive evidence for causality in LQTS with atypical features, including neonatal atrioventricular block. The remaining gene (CACNA1C) had moderate level evidence for causing LQTS.

Conclusions:

More than half of the genes reported as causing LQTS have limited or disputed evidence to support their disease causation. Genetic variants in these genes should not be used for clinical decision-making, unless accompanied by new and sufficient genetic evidence. The findings of insufficient evidence to support gene-disease associations may extend to other disciplines of medicine and warrants a contemporary evidence-based evaluation for previously reported disease-causing genes to ensure their appropriate use in precision medicine.

Towards Precision Medicine With Human iPSCs for Cardiac Channelopathies

Long-QT syndrome, a frequently fatal inherited arrhythmia syndrome caused by genetic variants (congenital) or drugs (acquired), affects 1 in 2000 people worldwide. Its sentinel event is often sudden cardiac death, which makes preclinical diagnosis by genetic testing potentially life-saving. Unfortunately, clinical experience with genetic testing has shown that it is difficult to correctly identify genetic variants as disease causing. These current deficiencies in accurately assigning pathogenicity led to the discovery of increasing numbers of rare variants classified as variant of uncertain significance. To overcome these challenges, new technologies such as clustered regularly interspaced short palindromic repeats (CRISPR) genome editing can be combined with human induced pluripotent stem cell-derived cardiomyocytes to provide a new approach to decipher pathogenicity of variants of uncertain significance and to better predict arrhythmia risk. To that end, the overarching goal of our network is to establish the utility of induced pluripotent stem cell-based platforms to solve major clinical problems associated with long-QT syndrome by determining how to (1) differentiate pathogenic mutations from background genetic noise, (2) assess existing and novel variants associated with congenital and acquired long-QT syndrome, and (3) provide genotype- and phenotype- guided risk stratification and pharmacological management of long-QT syndrome. To achieve these goals and to further advance the use of induced pluripotent stem cells in disease modeling and drug discovery, our team of investigators for this Leducq Foundation Transatlantic Networks of Excellence proposal will work together to (1) improve differentiation efficiency, cellular maturation, and lineage specificity, (2) develop new assays for high throughput cellular phenotyping, and (3) train young investigators to clinically implement patient-specific genetic modeling.

Beyond the One Gene-One Disease Paradigm: Complex Genetics and Pleiotropy in Inheritable Cardiac Disorders

Inheritable cardiac disorders, which may be associated with cardiomyopathic changes, are often associated with increased risk of sudden death in the young. Early linkage analysis studies in Mendelian forms of these diseases, such as hypertrophic cardiomyopathy and long-QT syndrome, uncovered large-effect genetic variants that contribute to the phenotype. In more recent years, through genotype-phenotype studies and methodological advances in genetics, it has become evident that most inheritable cardiac disorders are not monogenic but, rather, have a complex genetic basis wherein multiple genetic variants contribute (oligogenic or polygenic inheritance). Conversely, studies on genes underlying these disorders uncovered pleiotropic effects, with a single gene affecting multiple and apparently unrelated phenotypes. In this review, we explore these 2 phenomena: on the one hand, the evidence that variants in multiple genes converge to generate one clinical phenotype, and, on the other, the evidence that variants in one gene can lead to apparently unrelated phenotypes. Although multiple conditions are addressed to illustrate these concepts, the experience obtained in the study of long-QT syndrome, Brugada syndrome, and arrhythmogenic cardiomyopathy, and in the study of functions related to SCN5A (the gene coding for the α-subunit of the most abundant sodium channel in the heart) and PKP2 (the gene coding for the desmosomal protein plakophilin-2), as well, is discussed in more detail.

A computational model of induced pluripotent stem-cell derived cardiomyocytes incorporating experimental variability from multiple data sources

Key points

Induced pluripotent stem cell‐derived cardiomyocytes (iPSC‐CMs) capture patient‐specific genotype–phenotype relationships, as well as cell‐to‐cell variability of cardiac electrical activity

Computational modelling and simulation provide a high throughput approach to reconcile multiple datasets describing physiological variability, and also identify vulnerable parameter regimes

We have developed a whole‐cell model of iPSC‐CMs, composed of single exponential voltage‐dependent gating variable rate constants, parameterized to fit experimental iPSC‐CM outputs

We have utilized experimental data across multiple laboratories to model experimental variability and investigate subcellular phenotypic mechanisms in iPSC‐CMs

This framework links molecular mechanisms to cellular‐level outputs by revealing unique subsets of model parameters linked to known iPSC‐CM phenotypes

Abstract

There is a profound need to develop a strategy for predicting patient‐to‐patient vulnerability in the emergence of cardiac arrhythmia. A promising in vitro method to address patient‐specific proclivity to cardiac disease utilizes induced pluripotent stem cell‐derived cardiomyocytes (iPSC‐CMs). A major strength of this approach is that iPSC‐CMs contain donor genetic information and therefore capture patient‐specific genotype–phenotype relationships. A cited detriment of iPSC‐CMs is the cell‐to‐cell variability observed in electrical activity. We postulated, however, that cell‐to‐cell variability may constitute a strength when appropriately utilized in a computational framework to build cell populations that can be employed to identify phenotypic mechanisms and pinpoint key sensitive parameters. Thus, we have exploited variation in experimental data across multiple laboratories to develop a computational framework for investigating subcellular phenotypic mechanisms. We have developed a whole‐cell model of iPSC‐CMs composed of simple model components comprising ion channel models with single exponential voltage‐dependent gating variable rate constants, parameterized to fit experimental iPSC‐CM data for all major ionic currents. By optimizing ionic current model parameters to multiple experimental datasets, we incorporate experimentally‐observed variability in the ionic currents. The resulting population of cellular models predicts robust inter‐subject variability in iPSC‐CMs. This approach links molecular mechanisms to known cellular‐level iPSC‐CM phenotypes, as shown by comparing immature and mature subpopulations of models to analyse the contributing factors underlying each phenotype. In the future, the presented models can be readily expanded to include genetic mutations and pharmacological interventions for studying the mechanisms of rare events, such as arrhythmia triggers.

Induced pluripotent stem cell‐derived cardiomyocytes (iPSC‐CMs) capture patient‐specific genotype–phenotype relationships, as well as cell‐to‐cell variability of cardiac electrical activity

Computational modelling and simulation provide a high throughput approach to reconcile multiple datasets describing physiological variability, and also identify vulnerable parameter regimes

We have developed a whole‐cell model of iPSC‐CMs, composed of single exponential voltage‐dependent gating variable rate constants, parameterized to fit experimental iPSC‐CM outputs

We have utilized experimental data across multiple laboratories to model experimental variability and investigate subcellular phenotypic mechanisms in iPSC‐CMs

This framework links molecular mechanisms to cellular‐level outputs by revealing unique subsets of model parameters linked to known iPSC‐CM phenotypes

Genetic susceptibility in pharmacodynamic and pharmacokinetic pathways underlying drug-induced arrhythmia and sudden unexplained deaths

Drug-induced arrhythmia is an adverse drug reaction that can be potentially fatal since it is mostly related to drug-induced QT prolongation, a known risk factor for Torsade de Pointes and sudden cardiac death (SCD). Several risk factors have been described in association to these drug-induced events, such as preexistent cardiac disease and genetic variation. Our objective was to study the genetic susceptibility in pharmacodynamic and pharmacokinetic pathways underlying suspected drug-induced arrhythmias and sudden unexplained deaths in 32 patients. The genetic component in the pharmacodynamic pathway was studied by analysing 96 genes associated with higher risk of SCD through massive parallel sequencing. Pharmacokinetic-mediated genetic susceptibility was investigated by studying the genes encoding cytochrome P450 enzymes using medium-throughput genotyping. Pharmacodynamic analysis showed three probably pathogenic variants and 45 variants of uncertain significance in 28 patients, several of them previously described in relation to mild or late onset cardiomyopathies. These results suggest that genetic variants in cardiomyopathy genes, in addition to those related with channelopathies, could be relevant to drug-induced cardiotoxicity and contribute to the arrhythmogenic phenotype. Pharmacokinetic analysis showed three patients that could have an altered metabolism of the drugs they received involving CYP2C19 and/or CYP2D6, probably contributing to the arrhythmogenic phenotype. The study of genetic variants in both pharmacodynamic and pharmacokinetic pathways may be a useful strategy to understand the multifactorial mechanism of drug-induced events in both clinical practice and forensic field. However, it is necessary to comprehensively study and evaluate the contribution of the genetic susceptibility to drug-induced cardiotoxicity.

SCN5A (NaV1.5) Variant Functional Perturbation and Clinical Presentation: Variants of a Certain Significance

BACKGROUND

Accurately predicting the impact of rare nonsynonymous variants on disease risk is an important goal in precision medicine. Variants in the cardiac sodium channel SCN5A (protein Na_V1.5; voltage-dependent cardiac Na+ channel) are associated with multiple arrhythmia disorders, including Brugada syndrome and long QT syndrome. Rare SCN5A variants also occur in ≈1% of unaffected individuals. We hypothesized that in vitro electrophysiological functional parameters explain a statistically significant portion of the variability in disease penetrance.

METHODS

From a comprehensive literature review, we quantified the number of carriers presenting with and without disease for 1712 reported SCN5A variants. For 356 variants, data were also available for 5 Na_V1.5 electrophysiological parameters: peak current, late/persistent current, steady-state V1/2 of activation and inactivation, and recovery from inactivation.

RESULTS

We found that peak and late current significantly associate with Brugada syndrome (P<0.001; ρ=-0.44; Spearman rank test) and long QT syndrome disease penetrance (P<0.001; ρ=0.37). Steady-state V1/2 activation and recovery from inactivation associate significantly with Brugada syndrome and long QT syndrome penetrance, respectively. Continuous estimates of disease penetrance align with the current American College of Medical Genetics classification paradigm.

CONCLUSIONS

Na_V1.5 in vitro electrophysiological parameters are correlated with Brugada syndrome and long QT syndrome disease risk. Our data emphasize the value of in vitro electrophysiological characterization and incorporating counts of affected and unaffected carriers to aid variant classification. This quantitative analysis of the electrophysiological literature should aid the interpretation of Na_V1.5 variant electrophysiological abnormalities and help improve Na_V1.5 variant classification.

Classification and Reporting of Potentially Proarrhythmic Common Genetic Variation in Long QT Syndrome Genetic Testing

The acquired and congenital forms of long QT syndrome represent 2 distinct but clinically and genetically intertwined disorders of cardiac repolarization characterized by the shared final common pathway of QT interval prolongation and risk of potentially life-threatening arrhythmias. Over the past 2 decades, our understanding of the spectrum of genetic variation that (1) perturbs the function of cardiac ion channel macromolecular complexes and intracellular calcium-handling proteins, (2) underlies acquired/congenital long QT syndrome susceptibility, and (3) serves as a determinant of QT interval duration in the general population has grown exponentially. In turn, these molecular insights led to the development and increased utilization of clinically impactful genetic testing for congenital long QT syndrome. However, the widespread adoption and potential misinterpretation of the 2015 American College of Medical Genetics and Genomics variant classification and reporting guidelines may have contributed unintentionally to the reduced reporting of common genetic variants, with compelling epidemiological and functional evidence to support a potentially proarrhythmic role in patients with congenital and acquired long QT syndrome. As a result, some genetic testing reports may fail to convey the full extent of a patient's genetic susceptibility for a potentially life-threatening arrhythmia to the ordering healthcare professional. In this white paper, we examine the current classification and reporting (or lack thereof) of potentially proarrhythmic common genetic variants and investigate potential mechanisms to facilitate the reporting of these genetic variants without increasing the risk of diagnostic miscues.

Citalopram and the KCNE1 D85N variant: a case report on the implications of a genetic modifier

Background

Prolongation of the QT interval on the electrocardiogram is clinically important due to the association with an increased risk of sudden cardiac death. A long QT interval may be genetically determined (congenital long QT syndrome) or be drug-induced long QT syndrome e.g. caused by pharmaceutical drugs and electrolyte imbalances.

Case summary

In this report, we describe the case a 54-year-old woman, who presented with syncope. At presentation, the QTc interval was markedly prolonged, and she was admitted for observation under telemetry. The following day the patient had experienced a near syncope during an episode of 18 s of Torsade de Pointes (TdP). At the time of TdP, the potassium level (3.4 mmol/L) was mildly reduced, and the ECG showed a QTc interval of 640 ms. In spite of correction of hypokalaemia and discontinuation of the possibly LQTS-inducing drug citalopram the QTc duration remained intermittently prolonged. A transthoracic echocardiogram and a recent coronary angiogram were normal. The patient received an implantable cardioverter-defibrillator. Subsequent genetic testing identified a heterozygous KCNE1 p.D85N (c.253G>A) variant, a known QT modifier with a population prevalence of 1.3%.

Discussion

We conclude that the combination of a commonly prescribed antidepressant, discrete hypokalaemia, and a common KCNE1 QT modifier may cause severe QTc prolongation and life-threatening arrhythmia.

Modifier genes for sudden cardiac death

Genetic conditions, even those associated with identical gene mutations, can present with variable clinical manifestations. One widely accepted explanation for this phenomenon is the existence of genetic factors capable of modifying the consequences of disease-causing mutations (modifier genes). Here, we address the concepts and principles by which genetic factors may be involved in modifying risk for cardiac arrhythmia, then discuss the current knowledge and interpretation of their contribution to clinical heterogeneity. We illustrate these concepts in the context of two important clinical conditions associated with risk for sudden cardiac death including a monogenic disorder (congenital long QT syndrome) in which the impact of modifier genes has been established, and a complex trait (life-threatening arrhythmias in acute myocardial infarction) for which the search for genetic modifiers of arrhythmic risk is more challenging. Advances in understanding the contribution of modifier genes to a higher or lower propensity towards sudden death should improve patient-specific risk stratification and be a major step towards precision medicine.

Catecholaminergic polymorphic ventricular tachycardia patients with multiple genetic variants in the PACES CPVT Registry

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is often a life-threatening arrhythmia disorder with variable penetrance and expressivity. Little is known about the incidence or outcomes of CPVT patients with ≥2 variants.

METHODS

The phenotypes, genotypes and outcomes of patients in the Pediatric and Congenital Electrophysiology Society CPVT Registry with ≥2 variants in genes linked to CPVT were ascertained. The American College of Medical Genetics & Genomics (ACMG) criteria and structural mapping were used to predict the pathogenicity of variants (3D model of pig RyR2 in open-state).

RESULTS

Among 237 CPVT subjects, 193 (81%) had genetic testing. Fifteen patients (8%) with a median age of 9 years (IQR 5-12) had ≥2 variants. Sudden cardiac arrest occurred in 11 children (73%), although none died during a median follow-up of 4.3 years (IQR 2.5-6.1). Thirteen patients (80%) had at least two RYR2 variants, while the remaining two patients had RYR2 variants plus variants in other CPVT-linked genes. Among all variants identified, re-classification of the commercial laboratory interpretation using ACMG criteria led to the upgrade from variant of unknown significance (VUS) to pathogenic/likely pathogenic (P/LP) for 5 variants, and downgrade from P/LP to VUS for 6 variants. For RYR2 variants, 3D mapping using the RyR2 model suggested that 2 VUS by ACMG criteria were P/LP, while 2 variants were downgraded to likely benign.

CONCLUSIONS

This severely affected cohort demonstrates that a minority of CPVT cases are related to ≥2 variants, which may have implications on family-based genetic counselling. While multi-variant CPVT patients were at high-risk for sudden cardiac arrest, there are insufficient data to conclude that this genetic phenomenon has prognostic implications at present. Further research is needed to determine the significance and generalizability of this observation. This study also shows that a rigorous approach to variant re-classification using the ACMG criteria and 3D mapping is important in reaching an accurate diagnosis, especially in the multi-variant population.

Ondansetron blocks wild-type and p.F503L variant small-conductance Ca2+-activated K+ channels

Apamin-sensitive small-conductance Ca2+-activated K+ (SK) current ( IKAS) is encoded by Ca2+-activated K+ channel subfamily N ( KCNN) genes. IKAS importantly contributes to cardiac repolarization in conditions associated with reduced repolarization reserve. To test the hypothesis that IKAS inhibition contributes to drug-induced long QT syndrome (diLQTS), we screened for KCNN variants among patients with diLQTS, determined the properties of heterologously expressed wild-type (WT) and variant KCNN channels, and determined if the 5-HT3 receptor antagonist ondansetron blocks IKAS. We searched 2,306,335 records in the Indiana Network for Patient Care and found 11 patients with diLQTS who had DNA available in the Indiana Biobank. DNA sequencing discovered a heterozygous KCNN2 variant (p.F503L) in a 52-yr-old woman presenting with corrected QT interval prolongation at baseline (473 ms) and further corrected QT interval lengthening (601 ms) after oral administration of ondansetron. That patient was also heterozygous for the p.S38G and p.P2835S variants of the QT-controlling genes KCNE1 and ankyrin 2, respectively. Patch-clamp experiments revealed that the p.F503L KCNN2 variant heterologously expressed in human embryonic kidney (HEK)-293 cells augmented Ca2+ sensitivity, increasing IKAS density. The fraction of total F503L-KCNN2 protein retained in the membrane was higher than that of WT KCNN2 protein. Ondansetron at nanomolar concentrations inhibited WT and p.F503L SK2 channels expressed in HEK-293 cells as well as native SK channels in ventricular cardiomyocytes. Ondansetron-induced IKAS inhibition was also demonstrated in Langendorff-perfused murine hearts. In conclusion, the heterozygous p.F503L KCNN2 variant increases Ca2+ sensitivity and IKAS density in transfected HEK-293 cells. Ondansetron at therapeutic (i.e., nanomolar) concentrations is a potent IKAS blocker. NEW & NOTEWORTHY We showed that ondansetron, a 5-HT3 receptor antagonist, blocks small-conductance Ca2+-activated K+ (SK) current. Ondansetron may be useful in controlling arrhythmias in which increased SK current is a likely contributor. However, its SK-blocking effects may also facilitate the development of drug-induced long QT syndrome.