Long QT syndrome type 5-Lite: Defining the clinical phenotype associated with the potentially proarrhythmic p.Asp85Asn-KCNE1 common genetic variant

Multi-site validation of a functional assay to adjudicate SCN5A Brugada Syndrome-associated variants

Brugada Syndrome (BrS) is an inheritable arrhythmia condition that is associated with rare, loss-of-function variants in the cardiac sodium channel gene, SCN5A. Interpreting the pathogenicity of SCN5A missense variants is challenging and ~79% of SCN5A missense variants in ClinVar are currently classified as Variants of Uncertain Significance (VUS). An in vitro SCN5A-BrS automated patch clamp assay was generated for high-throughput functional studies of NaV1.5. The assay was independently studied at two separate research sites - Vanderbilt University Medical Center and Victor Chang Cardiac Research Institute - revealing strong correlations, including peak INa density (R2=0.86). The assay was calibrated according to ClinGen Sequence Variant Interpretation recommendations using high-confidence variant controls (n=49). Normal and abnormal ranges of function were established based on the distribution of benign variant assay results. The assay accurately distinguished benign controls (24/25) from pathogenic controls (23/24). Odds of Pathogenicity values derived from the experimental results yielded 0.042 for normal function (BS3 criterion) and 24.0 for abnormal function (PS3 criterion), resulting in up to strong evidence for both ACMG criteria. The calibrated assay was then used to study SCN5A VUS observed in four families with BrS and other arrhythmia phenotypes associated with SCN5A loss-of-function. The assay revealed loss-of-function for three of four variants, enabling reclassification to likely pathogenic. This validated APC assay provides clinical-grade functional evidence for the reclassification of current VUS and will aid future SCN5A-BrS variant classification.

Post-mortem genetic testing in sudden cardiac death and genetic screening of relatives at risk: lessons learned from a Czech pilot multidisciplinary study

Sudden cardiac death (SCD) might have an inherited cardiac condition background. Genetic testing supports post-mortem diagnosis and screening of relatives at risk. Our aim is to determine the feasibility of a Czech national collaboration group and to establish the clinical importance of molecular autopsy and family screening. From 2016 to 2021, we have evaluated 100 unrelated SCD cases (71.0% males, age: 33.3 (12.8) years). Genetic testing was performed by next-generation sequencing utilizing a panel of 100 genes related to inherited cardiac/aortic conditions and/or whole exome sequencing. According to autopsy, cases were divided into cardiomyopathies, sudden arrhythmic death syndrome, sudden unexplained death syndrome, and sudden aortic death. We identified pathogenic/likely pathogenic variants following ACMG/AMP recommendations in 22/100 (22.0%) of cases. Since poor DNA quality, we have performed indirect DNA testing in affected relatives or in healthy parents reaching a diagnostic genetic yield of 11/24 (45.8%) and 1/10 (10.0%), respectively. Cardiological and genetic screening disclose 83/301 (27.6%) relatives at risk of SCD. Genetic testing in affected relatives as starting material leads to a high diagnostic yield offering a valuable alternative when suitable material is not available. This is the first multidisciplinary/multicenter molecular autopsy study in the Czech Republic which supports the establishment of this type of diagnostic tests. A central coordinator and proper communication among centers are crucial for the success of a collaboration at a national level.

Continuous Bayesian variant interpretation accounts for incomplete penetrance among Mendelian cardiac channelopathies

PURPOSE

The congenital Long QT Syndrome (LQTS) and Brugada Syndrome (BrS) are Mendelian autosomal dominant diseases that frequently precipitate fatal cardiac arrhythmias. Incomplete penetrance is a barrier to clinical management of heterozygotes harboring variants in the major implicated disease genes KCNQ1, KCNH2, and SCN5A. We apply and evaluate a Bayesian penetrance estimation strategy that accounts for this phenomenon.

METHODS

We generated Bayesian penetrance models for KCNQ1-LQT1 and SCN5A-LQT3 using variant-specific features and clinical data from the literature, international arrhythmia genetic centers, and population controls. We analyzed the distribution of posterior penetrance estimates across 4 genotype-phenotype relationships and compared continuous estimates with ClinVar annotations. Posterior estimates were mapped onto protein structure.

RESULTS

Bayesian penetrance estimates of KCNQ1-LQT1 and SCN5A-LQT3 are empirically equivalent to 10 and 5 clinically phenotype heterozygotes, respectively. Posterior penetrance estimates were bimodal for KCNQ1-LQT1 and KCNH2-LQT2, with a higher fraction of missense variants with high penetrance among KCNQ1 variants. There was a wide distribution of variant penetrance estimates among identical ClinVar categories. Structural mapping revealed heterogeneity among "hot spot" regions and featured high penetrance estimates for KCNQ1 variants in contact with calmodulin and the S6 domain.

CONCLUSIONS

Bayesian penetrance estimates provide a continuous framework for variant interpretation.

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.

Estimating the Posttest Probability of Long QT Syndrome Diagnosis for Rare KCNH2 Variants

BACKGROUND

The proliferation of genetic profiling has revealed many associations between genetic variations and disease. However, large-scale phenotyping efforts in largely healthy populations, coupled with DNA sequencing, suggest variants currently annotated as pathogenic are more common in healthy populations than previously thought. In addition, novel and rare variants are frequently observed in genes associated with disease both in healthy individuals and those under suspicion of disease. This raises the question of whether these variants can be useful predictors of disease. To answer this question, we assessed the degree to which the presence of a variant in the cardiac potassium channel gene KCNH2 was diagnostically predictive for the autosomal dominant long QT syndrome.

METHODS

We estimated the probability of a long QT diagnosis given the presence of each KCNH2 variant using Bayesian methods that incorporated variant features such as changes in variant function, protein structure, and in silico predictions. We call this estimate the posttest probability of disease. Our method was applied to over 4000 individuals heterozygous for 871 missense or in-frame insertion/deletion variants in KCNH2 and validated against a separate international cohort of 933 individuals heterozygous for 266 missense or in-frame insertion/deletion variants.

RESULTS

Our method was well-calibrated for the observed fraction of heterozygotes diagnosed with long QT syndrome. Heuristically, we found that the innate diagnostic information one learns about a variant from 3-dimensional variant location, in vitro functional data, and in silico predictors is equivalent to the diagnostic information one learns about that same variant by clinically phenotyping 10 heterozygotes. Most importantly, these data can be obtained in the absence of any clinical observations.

CONCLUSIONS

We show how variant-specific features can inform a prior probability of disease for rare variants even in the absence of clinically phenotyped heterozygotes.

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.

When genetic burden reaches threshold

Rare cardiac genetic diseases have generally been considered to be broadly Mendelian in nature, with clinical genetic testing for these conditions predicated on the detection of a primary causative rare pathogenic variant that will enable cascade genetic screening in families. However, substantial variability in penetrance and disease severity among carriers of pathogenic variants, as well as the inability to detect rare Mendelian variants in considerable proportions of patients, indicates that more complex aetiologies are likely to underlie these diseases. Recent findings have suggested genetic variants across a range of population frequencies and effect sizes may combine, along with non-genetic factors, to determine whether the threshold for expression of disease is reached and the severity of the phenotype. The availability of increasingly large genetically characterized cohorts of patients with rare cardiac diseases is enabling the discovery of common genetic variation that may underlie both variable penetrance in Mendelian diseases and the genetic aetiology of apparently non-Mendelian rare cardiac conditions. It is likely that the genetic architecture of rare cardiac diseases will vary considerably between different conditions as well as between patients with similar phenotypes, ranging from near-Mendelian disease to models more akin to common, complex disease. Uncovering the broad range of genetic factors that predispose patients to rare cardiac diseases offers the promise of improved risk prediction and more focused clinical management in patients and their families.

Precision Medicine Approaches to Cardiac Arrhythmias: JACC Focus Seminar 4/5

In the initial 3 papers in this Focus Seminar series, the fundamentals and key concepts of precision medicine were reviewed, followed by a focus on precision medicine in the context of vascular disease and cardiomyopathy. For the remaining 2 papers, we focus on precision medicine in the context of arrhythmias. Specifically, in this fourth paper we focus on long QT syndrome, Brugada syndrome, and atrial fibrillation. The final (fifth) paper will deal with catecholaminergic polymorphic ventricular tachycardia. These arrhythmias represent a spectrum of disease ranging from common to relatively rare, with very different genetic and environmental causative factors, and with differing clinical manifestations that range from almost no consequences to lethality in childhood or adolescence if untreated. Accordingly, the emerging precision medicine approaches to these arrhythmias vary significantly, but several common themes include increased use of genetic testing, avoidance of triggers, and personalized risk stratification to guide the use of arrhythmia-specific therapies.

A computational model of induced pluripotent stem-cell derived cardiomyocytes for high throughput risk stratification of KCNQ1 genetic variants

In the last decade, there has been tremendous progress in identifying genetic anomalies linked to clinical disease. New experimental platforms have connected genetic variants to mechanisms underlying disruption of cellular and organ behavior and the emergence of proarrhythmic cardiac phenotypes. The development of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) signifies an important advance in the study of genetic disease in a patient-specific context. However, considerable limitations of iPSC-CM technologies have not been addressed: 1) phenotypic variability in apparently identical genotype perturbations, 2) low-throughput electrophysiological measurements, and 3) an immature phenotype which may impact translation to adult cardiac response. We have developed a computational approach intended to address these problems. We applied our recent iPSC-CM computational model to predict the proarrhythmic risk of 40 KCNQ1 genetic variants. An I_Ks computational model was fit to experimental data for each mutation, and the impact of each mutation was simulated in a population of iPSC-CM models. Using a test set of 15 KCNQ1 mutations with known clinical long QT phenotypes, we developed a method to stratify the effects of KCNQ1 mutations based on proarrhythmic markers. We utilized this method to predict the severity of the remaining 25 KCNQ1 mutations with unknown clinical significance. Tremendous phenotypic variability was observed in the iPSC-CM model population following mutant perturbations. A key novelty is our reporting of the impact of individual KCNQ1 mutant models on adult ventricular cardiomyocyte electrophysiology, allowing for prediction of mutant impact across the continuum of aging. This serves as a first step toward translating predicted response in the iPSC-CM model to predicted response of the adult ventricular myocyte given the same genetic mutation. As a whole, this study presents a new computational framework that serves as a high throughput method to evaluate risk of genetic mutations based-on proarrhythmic behavior in phenotypically variable populations.

In the last decade, there has been tremendous progress in identifying genetic mutations linked to clinical diseases, such as cardiac arrhythmia. Many experimental platforms have been developed to study this link, including induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). IPSC-CMs are patient-derived cardiac cells which allow for the study of genetic variants within a patient-specific context. However, experimentally iPSC-CMs have certain limitations, including: (1) they exhibit variability in behavior within cells that are apparently genetically identical, and (2) they are immature compared to adult cardiac cells. In our study, we have developed a computational approach to model 40 genetic variants in the KCNQ1 gene and predict the proarrhythmic risk of each variant. To do this, we modeled the ionic current determined by KCNQ1, I_Ks, to fit experimental data for each mutation. We then simulated the impact of each mutation in a population of iPSC-CMs, incorporating variability across the population. We also simulated each variant in an adult cardiac cell model, providing a link between iPSC-CM response to mutants and adult cardiac cell response to the same mutants. Overall, this study provides a new computational framework to evaluate risk of genetic mutations based-on proarrhythmic behavior diverse populations of iPSC-CM models.

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.

An International Multicenter Evaluation of Type 5 Long QT Syndrome: A Low Penetrant Primary Arrhythmic Condition

BACKGROUND

Insight into type 5 long QT syndrome (LQT5) has been limited to case reports and small family series. Improved understanding of the clinical phenotype and genetic features associated with rare KCNE1 variants implicated in LQT5 was sought through an international multicenter collaboration.

METHODS

Patients with either presumed autosomal dominant LQT5 (N = 229) or the recessive Type 2 Jervell and Lange-Nielsen syndrome (N = 19) were enrolled from 22 genetic arrhythmia clinics and 4 registries from 9 countries. KCNE1 variants were evaluated for ECG penetrance (defined as QTc >460 ms on presenting ECG) and genotype-phenotype segregation. Multivariable Cox regression was used to compare the associations between clinical and genetic variables with a composite primary outcome of definite arrhythmic events, including appropriate implantable cardioverter-defibrillator shocks, aborted cardiac arrest, and sudden cardiac death.

RESULTS

A total of 32 distinct KCNE1 rare variants were identified in 89 probands and 140 genotype positive family members with presumed LQT5 and an additional 19 Type 2 Jervell and Lange-Nielsen syndrome patients. Among presumed LQT5 patients, the mean QTc on presenting ECG was significantly longer in probands (476.9±38.6 ms) compared with genotype positive family members (441.8±30.9 ms, P<0.001). ECG penetrance for heterozygous genotype positive family members was 20.7% (29/140). A definite arrhythmic event was experienced in 16.9% (15/89) of heterozygous probands in comparison with 1.4% (2/140) of family members (adjusted hazard ratio [HR] 11.6 [95% CI, 2.6-52.2]; P=0.001). Event incidence did not differ significantly for Type 2 Jervell and Lange-Nielsen syndrome patients relative to the overall heterozygous cohort (10.5% [2/19]; HR 1.7 [95% CI, 0.3-10.8], P=0.590). The cumulative prevalence of the 32 KCNE1 variants in the Genome Aggregation Database, which is a human database of exome and genome sequencing data from now over 140 000 individuals, was 238-fold greater than the anticipated prevalence of all LQT5 combined (0.238% vs 0.001%).

CONCLUSIONS

The present study suggests that putative/confirmed loss-of-function KCNE1 variants predispose to QT prolongation, however, the low ECG penetrance observed suggests they do not manifest clinically in the majority of individuals, aligning with the mild phenotype observed for Type 2 Jervell and Lange-Nielsen syndrome patients.

Pre-Test Probability and Genes and Variants of Uncertain Significance in Familial Long QT Syndrome

The genetics underlying familial long QT syndrome (LQTS) are among the best characterised of all of the inherited heart conditions. Cohort and registry studies have demonstrated important genotype-phenotype correlations that are now essential in guiding clinical practice of patients with the most common three genotypes; KCNQ1 (LQT type 1), KCNH2 (LQT type 2) and SCN5A (LQT type 3). However, the growing number of genes-now more than 16-is confusing, and there is much doubt as to whether many actually cause LQTS at all. Furthermore, changes in sequencing techniques, evolving variant classification criteria and new scientific discoveries make all genes and variants subject to a continuous process of re-classification. This review discusses the nature of variant adjudication, the important concept of pre-test probability in interpreting a genetic result and how the nomenclature of LQTS is shifting in response to this new knowledge. It further discusses the role of deep phenotyping, the inclusion of evaluation of family members in interpreting a genetic test result, or even deciding if genetic testing should occur at all, and the role of specialist multidisciplinary teams to translate this continuously evolving knowledge into the best clinical advice, in partnership with referring cardiologists.

Recent understanding of clinical sequencing and gene-based risk stratification in inherited primary arrhythmia syndrome

Inherited primary arrhythmia syndromes (IPAS) may result in ventricular tachycardia or ventricular fibrillation by some genetic disorders, leading to sudden cardiac death. IPAS are also called "channelopathies" since many of these are caused by an abnormality in myocardial ion channels. Congenital long-QT syndrome (LQTS) is the most well documented IPAS, which may be seen in 0.1% of the general population. More than 15 disease-causing genes have been identified in almost 70% of LQTS patients and genetic testing is well applied to not only clinical diagnosis but also risk stratification and gene-based therapeutic strategy for each person with LQTS. Thus, in LQTS, gene-based personalized medicine can be realized. Unlike the LQTS, genetic testing for the Brugada syndrome (BrS) is still controversial since only 20% of patients can be identified with the causing gene mutations, most of which are in SCN5A. Furthermore, even in the SCN5A mutation-positive carriers, their phenotypes are not completely consistent with BrS, but may cause other IPAS including LQTS, cardiac conduction defect, sick sinus syndrome, and dilated cardiomyopathy. On the other hand, a recent Japanese BrS registry demonstrated that the pore-region mutations in SCN5A are significantly associated with a risk of lethal cardiac events. Furthermore, a genome-wide association study revealed that a common variant in SCN10A or HEY2 in addition to SCN5A is associated with BrS, thus, BrS may not be a monogenic Mendelian disease but probably an oligogenic disease. The purpose of this review is to describe the basic genetic and pathophysiological findings of the IPAS, particularly LQTS and Brugada syndrome, and to outline a rational approach to genetic testing, management, and family screening.

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.