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Background: Cardiac sodium channel β-subunit mutations have been associated with several inherited cardiac arrhythmia syndromes.Objective: To identify and characterize variations in SCN1Bb associated with Brugada syndrome (BrS) and sudden infant death syndrome (SIDS).Methods: All known exons and intron borders of the BrS-susceptibility genes were amplified and sequenced in both directions. Wild type (WT) and mutant genes were expressed in TSA201 cells and studied using co-immunoprecipitation and whole-cell patch-clamp techniques.Results: Patient 1 was a 44-year-old man with an ajmaline-induced type 1 ST-segment elevation in V1 and V2 supporting the diagnosis of BrS. Patient 2 was a 62-year-old woman displaying a coved-type BrS electrocardiogram who developed cardiac arrest during fever. Patient 3 was a 4-month-old female SIDS case. A R214Q variant was detected in exon 3A of SCN1Bb (Na(v)1B) in all three probands, but not in any other gene previously associated with BrS or SIDS. R214Q was identified in 4 of 807 ethnically-matched healthy controls (0.50%). Co-expression of SCN5A/WT + SCN1Bb/R214Q resulted in peak sodium channel current (I(Na)) 56.5% smaller compared to SCN5A/WT + SCN1Bb/WT (n = 11-12, P<0.05). Co-expression of KCND3/WT + SCN1Bb/R214Q induced a Kv4.3 current (transient outward potassium current, I(to)) 70.6% greater compared with KCND3/WT + SCN1Bb/WT (n = 10-11, P<0.01). Co-immunoprecipitation indicated structural association between Na(v)β1B and Na(v)1.5 and K(v)4.3.Conclusion: Our results suggest that R214Q variation in SCN1Bb is a functional polymorphism that may serve as a modifier of the substrate responsible for BrS or SIDS phenotypes via a combined loss of function of sodium channel current and gain of function of transient outward potassium current. [ABSTRACT FROM AUTHOR]

Background: Brugada syndrome (BrS) is a sudden death-predisposing genetic condition characterized electrocardiographically by ST segment elevation in the leads V(1)-V(3). Given the prominent role of the transient outward current (I(to)) in BrS pathogenesis, we hypothesized that rare gain-of-function mutations in KCND3 may serve as a pathogenic substrate for BrS.Methods: Comprehensive mutational analysis of KCND3-encoded Kv4.3 (I(to)) was conducted using polymerase chain reaction, denaturing high performance liquid chromatography, and direct sequencing of DNA derived from 86 unrelated BrS1-8 genotype-negative BrS patients. DNA from 780 healthy individuals was examined to assess allelic frequency for nonsynonymous variants. Putative BrS-associated Kv4.3 mutations were engineered and coexpressed with wild-type KChIP2 in HEK293 cells. Wild-type and mutant I(to) ion currents were recorded using whole-cell patch clamp.Results: Two BrS1-8 genotype-negative cases possessed novel Kv4.3 missense mutations. Both Kv4.3-L450F and Kv4.3-G600R were absent in 1,560 reference alleles and involved residues highly conserved across species. Both Kv4.3-L450F and Kv4.3-G600R demonstrated a gain-of-function phenotype, increasing peak I(to) current density by 146.2% (n = 15, P <.05) and 50.4% (n = 15, P <.05), respectively. Simulations using a Luo-Rudy II action potential (AP) model demonstrated the stable loss of the AP dome as a result of the increased I(to) maximal conductance associated with the heterozygous expression of either L450F or G600R.Conclusions: These findings provide the first molecular and functional evidence implicating novel KCND3 gain-of-function mutations in the pathogenesis and phenotypic expression of BrS, with the potential for a lethal arrhythmia being precipitated by a genetically enhanced I(to) current gradient within the right ventricle where KCND3 expression is the highest. [ABSTRACT FROM AUTHOR]

Background: J-wave syndromes have emerged conceptually to encompass the pleiotropic expression of J-point abnormalities including Brugada syndrome (BrS) and early repolarization syndrome (ERS). KCNJ8, which encodes the cardiac K(ATP) Kir6.1 channel, recently has been implicated in ERS following identification of the functionally uncharacterized missense mutation S422L.Objective: The purpose of this study was to further explore KCNJ8 as a novel susceptibility gene for J-wave syndromes.Methods: Using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct DNA sequencing, comprehensive open reading frame/splice site mutational analysis of KCNJ8 was performed in 101 unrelated patients with J-wave syndromes, including 87 with BrS and 14 with ERS. Six hundred healthy individuals were examined to assess the allelic frequency for all variants detected. KCNJ8 mutation(s) was engineered by site-directed mutagenesis and coexpressed heterologously with SUR2A in COS-1 cells. Ion currents were recorded using whole-cell configuration of the patch-clamp technique.Results: One BrS case and one ERS case hosted the identical missense mutation S422L, which was reported previously. KCNJ8-S422L involves a highly conserved residue and was absent in 1,200 reference alleles. Both cases were negative for mutations in all known BrS and ERS susceptibility genes. K(ATP) current of the Kir6.1-S422L mutation was increased significantly over the voltage range from 0 to 40 mV compared to Kir6.1-WT channels (n = 16-21; P <.05).Conclusion: These findings further implicate KCNJ8 as a novel J-wave syndrome susceptibility gene and a marked gain of function in the cardiac K(ATP) Kir6.1 channel secondary to KCNJ8-S422L as a novel pathogenic mechanism for the phenotypic expression of both BrS and ERS. [ABSTRACT FROM AUTHOR]

Background: Approximately 10% of sudden infant death syndrome (SIDS) cases may stem from potentially lethal cardiac channelopathies, with approximately half of channelopathic SIDS involving the Na(V)1.5 cardiac sodium channel. Recently, Na(V) beta subunits have been implicated in various cardiac arrhythmias. Thus, the 4 genes encoding Na(V) beta subunits represent plausible candidate genes for SIDS.Objective: This study sought to determine the spectrum, prevalence, and functional consequences of sodium channel beta-subunit mutations in a SIDS cohort.Methods: In this institutional review board-approved study, mutational analysis of the 4 beta-subunit genes, SCN1B to 4B, was performed using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct DNA sequencing of DNA derived from 292 SIDS cases. Engineered mutations were coexpressed with SCN5A in HEK 293 cells and were whole-cell patch clamped. One of the putative SIDS-associated mutations was similarly studied in adenovirally transduced adult rat ventricular myocytes.Results: Three rare (absent in 200 to 800 reference alleles) missense mutations (beta3-V36M, beta3-V54G, and beta4-S206L) were identified in 3 of 292 SIDS cases. Compared with SCN5A+beta3-WT, beta3-V36M significantly decreased peak I(Na) and increased late I(Na), whereas beta3-V54G resulted in a marked loss of function. beta4-S206L accentuated late I(Na) and positively shifted the midpoint of inactivation compared with SCN5A+beta4-WT. In native cardiomyocytes, beta4-S206L accentuated late I(Na) and increased the ventricular action potential duration compared with beta4-WT.Conclusion: This study provides the first molecular and functional evidence to implicate the Na(V) beta subunits in SIDS pathogenesis. Altered Na(V)1.5 sodium channel function due to beta-subunit mutations may account for the molecular pathogenic mechanism underlying approximately 1% of SIDS cases. [ABSTRACT FROM AUTHOR]

Background: Long QT syndrome (LQTS) is a potentially lethal, highly treatable cardiac channelopathy for which genetic testing has matured from discovery to translation and now clinical implementation.Objectives: Here we examine the spectrum and prevalence of mutations found in the first 2,500 unrelated cases referred for the FAMILION LQTS clinical genetic test.Methods: Retrospective analysis of the first 2,500 cases (1,515 female patients, average age at testing 23 +/- 17 years, range 0 to 90 years) scanned for mutations in 5 of the LQTS-susceptibility genes: KCNQ1 (LQT1), KCNH2 (LQT2), SCN5A (LQT3), KCNE1 (LQT5), and KCNE2 (LQT6).Results: Overall, 903 referral cases (36%) hosted a possible LQTS-causing mutation that was absent in >2,600 reference alleles; 821 (91%) of the mutation-positive cases had single genotypes, whereas the remaining 82 patients (9%) had >1 mutation in > or =1 gene, including 52 cases that were compound heterozygous with mutations in >1 gene. Of the 562 distinct mutations, 394 (70%) were missense, 428 (76%) were seen once, and 336 (60%) are novel, including 92 of 199 in KCNQ1, 159 of 226 in KCNH2, and 70 of 110 in SCN5A.Conclusion: This cohort increases the publicly available compendium of putative LQTS-associated mutations by >50%, and approximately one-third of the most recently detected mutations continue to be novel. Although control population data suggest that the great majority of these mutations are pathogenic, expert interpretation of genetic test results will remain critical for effective clinical use of LQTS genetic test results. [ABSTRACT FROM AUTHOR]

OBJECTIVE: To perform a molecular autopsy involving the RyR2-encoded cardiac ryanodine receptor/calcium release channel to determine whether mutations responsible for catecholaminergic polymorphic ventricular tachycardia (CPVT) represent a novel pathogenic basis for unexplained drownings. METHODS: A cardiac channel molecular autopsy was performed on 2 individuals who died of unexplained drowning and whose cases were referred to the Sudden Death Genomics Laboratory at the Mayo Clinic in Rochester, Minn. Comprehensive mutational analysis of all 60 protein-encoded exons of the 5 long QT syndrome-causing cardiac channel genes and a targeted analysis of 18 RyR2 exons known to host RyR2-mediated CPVT-causing mutations (CPVT1) was performed using polymerase chain reaction, denaturing high-performance liquid chromatography, and DNA sequencing. RESULTS: Both individuals harbored novel mutations in RyR2. Postmortem mutational analysis revealed a familial missense mutation in exon 14, R414C, in a 16-year-old girl. A 9-year-old boy possessed a sporadic missense mutation in exon 49, V2475F. Both amino acid positions involve highly conserved residues that localize to critical functional domains in the calcium release channel. Neither substitution was present in 1000 reference alleles. CONCLUSIONS: This molecular autopsy study provides proof of principle that RyR2 mutations can underlie some unexplained drownings. A population-based genetic epidemiology study that involves molecular autopsies of individuals who die of unexplained drowning is needed to determine the prevalence and spectrum of KCNQ1 and now RyR2 mutations as potential pathogenic mechanisms for drowning. [ABSTRACT FROM AUTHOR]

OBJECTIVE: To perform a molecular autopsy of the RyR2-encoded cardiac ryanodine receptor/calcium release channel in medical examiner/coroner's cases of sudden unexplained death (SUD). METHODS: From September 1998 to March 2004, 49 cases of SUD were referred by medical examiners/coroners to the Sudden Death Genomics Laboratory at the Mayo Clinic in Rochester, Minn, for a cardiac channel molecular autopsy. Mutational analysis of 18 exons of RyR2 implicated previously in the pathogenesis of catecholaminergic polymorphic ventricular tachycardia (CPVT) was performed on genomic DNA using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct DNA sequencing. RESULTS: This cohort of 49 cases of SUD included 30 males, 13 with a family history of syncope, cardiac arrest, or sudden cardiac death (mean +/- SD age at death, 14.2 +/- 10.9 years). Six distinct RyR2 missense mutations (3 novel) were discovered in 7 cases (14%, 6 males, mean +/- SD age at death, 13.6 +/- 11.2 years) of SUD. The activities at the time of SUD were exertion (3), emotion (1), and unknown (3). The mutations, R420W, S2246L, N4097S, E4146K, T4158P, and R4497C, involved nonconservative amino acid substitutions in highly conserved residues across species and were not seen in 400 reference alleles. CONCLUSIONS: This study represents the first molecular autopsy of RyR2 in medical examiner-referred cases of SUD. A targeted analysis of only 18 of the 105 protein-encoding exons of the cardiac ryanodine receptor/calcium release channel revealed potential CPVT1-causing RyR2 mutations in 1 of every 7 cases of SUD. These findings suggest that postmortem genetic testing of RyR2 should be considered as a part of the comprehensive medicolegal autopsy investigation of a SUD case and that this potentially heritable and often elusive arrhythmia syndrome be scrutinized carefully in family members of those who experience SUD. [ABSTRACT FROM AUTHOR]

Objectives: This study was undertaken to determine the spectrum and prevalence of mutations in the RYR2-encoded cardiac ryanodine receptor in cases with exertional syncope and normal corrected QT interval (QTc).Background: Mutations in RYR2 cause type 1 catecholaminergic polymorphic ventricular tachycardia (CPVT1), a cardiac channelopathy with increased propensity for lethal ventricular dysrhythmias. Most RYR2 mutational analyses target 3 canonical domains encoded by <40% of the translated exons. The extent of CPVT1-associated mutations localizing outside of these domains remains unknown as RYR2 has not been examined comprehensively in most patient cohorts.Methods: Mutational analysis of all RYR2 exons was performed using polymerase chain reaction, high-performance liquid chromatography, and deoxyribonucleic acid sequencing on 155 unrelated patients (49% females, 96% Caucasian, age at diagnosis 20 +/- 15 years, mean QTc 428 +/- 29 ms), with either clinical diagnosis of CPVT (n = 110) or an initial diagnosis of exercise-induced long QT syndrome but with QTc <480 ms and a subsequent negative long QT syndrome genetic test (n = 45).Results: Sixty-three (34 novel) possible CPVT1-associated mutations, absent in 400 reference alleles, were detected in 73 unrelated patients (47%). Thirteen new mutation-containing exons were identified. Two-thirds of the CPVT1-positive patients had mutations that localized to 1 of 16 exons.Conclusions: Possible CPVT1 mutations in RYR2 were identified in nearly one-half of this cohort; 45 of the 105 translated exons are now known to host possible mutations. Considering that approximately 65% of CPVT1-positive cases would be discovered by selective analysis of 16 exons, a tiered targeting strategy for CPVT genetic testing should be considered. [ABSTRACT FROM AUTHOR]

Objectives: The aims of this study were to determine the spectrum and prevalence of "background genetic noise" in the arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC) genetic test and to determine genetic associations that can guide the interpretation of a positive test result.Background: ARVC is a potentially lethal genetic cardiovascular disorder characterized by myocyte loss and fibrofatty tissue replacement of the right ventricle. Genetic variation among the ARVC susceptibility genes has not been systematically examined, and little is known about the background noise associated with the ARVC genetic test.Methods: Using direct deoxyribonucleic acid sequencing, the coding exons/splice junctions of PKP2, DSP, DSG2, DSC2, and TMEM43 were genotyped for 93 probands diagnosed with ARVC from the Netherlands and 427 ostensibly healthy controls of various ethnicities. Eighty-two additional ARVC cases were obtained from published reports, and additional mutations were included from the ARVD/C Genetic Variants Database.Results: The overall yield of mutations among ARVC cases was 58% versus 16% in controls. Radical mutations were hosted by 0.5% of control individuals versus 43% of ARVC cases, while 16% of controls hosted missense mutations versus a similar 21% of ARVC cases. Relative to controls, mutations in cases occurred more frequently in non-Caucasians, localized to the N-terminal regions of DSP and DSG2, and localized to highly conserved residues within PKP2 and DSG2.Conclusions: This study is the first to comprehensively evaluate genetic variation in healthy controls for the ARVC susceptibility genes. Radical mutations are high-probability ARVC-associated mutations, whereas rare missense mutations should be interpreted in the context of race and ethnicity, mutation location, and sequence conservation. [ABSTRACT FROM AUTHOR]

Background: Hypertrophic cardiomyopathy (HCM) is a common genetic heart disease. Women with HCM tend to have a later onset but more severe disease course. However, the underlying pathobiological mechanisms for these differences remain unknown., Methods: Myectomy samples from 97 patients (53 males/44 females) with symptomatic obstructive HCM and 23 control cardiac tissues were included in this study. RNA-sequencing was performed on all samples. Mass spectrometry-based proteomics and phosphoproteomics was performed on a representative subset of samples., Results: The transcriptome, proteome, and phosphoproteome was similar between sexes and did not separate on PCA plotting. Overall, there were 482 differentially expressed genes (DEGs) between control females and control males while there were only 53 DEGs between HCM females and HCM males. There were 1983 DEGs between HCM females and control females compared to 1064 DEGs between HCM males and control males. Additionally, there was increased transcriptional downregulation of hypertrophy pathways in HCM females and in HCM males. HCM females had 119 differentially expressed proteins compared to control females while HCM males only had 27 compared to control males. Finally, the phosphoproteome showed females had 341 differentially phosphorylated proteins (DPPs) compared to controls while males only had 184. Interestingly, there was hypophosphorylation and inactivation of hypertrophy pathways in females but hyperphosphorylation and activation in males., Conclusion: There are subtle, but biologically relevant differences in the multi-omics profile of HCM. This study provides the most comprehensive atlas of sex-specific differences in the transcriptome, proteome, and phosphoproteome present at the time of surgical myectomy for obstructive HCM., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background: Genetic testing for cardiac channelopathies is the standard of care. However, many rare genetic variants remain classified as variants of uncertain significance (VUS) due to lack of epidemiological and functional data. Whether deep protein language models may aid in VUS resolution remains unknown. Here, we set out to compare how 2 deep protein language models perform at VUS resolution in the 3 most common long-QT syndrome-causative genes compared with the gold-standard patch clamp., Methods: A total of 72 rare nonsynonymous VUS (9 KCNQ1, 19 KCNH2 , and 50 SCN5A ) were engineered by site-directed mutagenesis and expressed in either HEK293 cells or TSA201 cells. Whole-cell patch-clamp technique was used to functionally characterize these variants. The protein language models, evolutionary scale modeling, version 1b and AlphaMissense, were used to predict the variant effect of missense variants and compared with patch clamp., Results: Considering variants in all 3 genes, the evolutionary scale modeling, version 1b model had a receiver operating characteristic curve-area under the curve of 0.75 ( P =0.0003). It had a sensitivity of 88% and a specificity of 50%. AlphaMissense performed well compared with patch-clamp with an receiver operating characteristic curve-area under the curve of 0.85 ( P <0.0001), sensitivity of 80%, and specificity of 76%., Conclusions: Deep protein language models aid in VUS resolution with high sensitivity but lower specificity. Thus, these tools cannot fully replace functional characterization but can aid in reducing the number of variants that may require functional analysis., Competing Interests: Dr Ackerman is a consultant for Abbott, BioMarin Pharmaceutical, Boston Scientific, Bristol Myers Squibb, Daiichi Sankyo, Illumina, Invitae, Medtronic, Solid Biosciences, Tenaya Therapeutics, and UpToDate. Dr Ackerman and Mayo Clinic are involved in an equity/intellectual property/royalty relationship with AliveCor, Anumana, ARMGO Pharma, Pfizer, and Thryv Therapeutics. However, none of these entities have contributed to this study in any manner. The other authors report no conflicts.

Background and Aims: Type 1 long QT syndrome (LQT1) is caused by pathogenic variants in the KCNQ1-encoded Kv7.1 potassium channels, which pathologically prolong ventricular action potential duration (APD). Herein, the pathologic phenotype in transgenic LQT1 rabbits is rescued using a novel KCNQ1 suppression-replacement (SupRep) gene therapy., Methods: KCNQ1-SupRep gene therapy was developed by combining into a single construct a KCNQ1 shRNA (suppression) and an shRNA-immune KCNQ1 cDNA (replacement), packaged into adeno-associated virus serotype 9, and delivered in vivo via an intra-aortic root injection (1E10 vg/kg). To ascertain the efficacy of SupRep, 12-lead electrocardiograms were assessed in adult LQT1 and wild-type (WT) rabbits and patch-clamp experiments were performed on isolated ventricular cardiomyocytes., Results: KCNQ1-SupRep treatment of LQT1 rabbits resulted in significant shortening of the pathologically prolonged QT index (QTi) towards WT levels. Ventricular cardiomyocytes isolated from treated LQT1 rabbits demonstrated pronounced shortening of APD compared to LQT1 controls, leading to levels similar to WT (LQT1-UT vs. LQT1-SupRep, P < .0001, LQT1-SupRep vs. WT, P = ns). Under β-adrenergic stimulation with isoproterenol, SupRep-treated rabbits demonstrated a WT-like physiological QTi and APD90 behaviour., Conclusions: This study provides the first animal-model, proof-of-concept gene therapy for correction of LQT1. In LQT1 rabbits, treatment with KCNQ1-SupRep gene therapy normalized the clinical QTi and cellular APD90 to near WT levels both at baseline and after isoproterenol. If similar QT/APD correction can be achieved with intravenous administration of KCNQ1-SupRep gene therapy in LQT1 rabbits, these encouraging data should compel continued development of this gene therapy for patients with LQT1., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Background: CaM (calmodulin)-mediated long-QT syndrome is a genetic arrhythmia disorder (calmodulinopathies) characterized by a high prevalence of life-threatening ventricular arrhythmias occurring early in life. Three distinct genes ( CALM1 , CALM2 , and CALM3 ) encode for the identical CaM protein. Conventional pharmacotherapies fail to adequately protect against potentially lethal cardiac events in patients with calmodulinopathy., Methods: Five custom-designed CALM1 -, CALM2 -, and CALM3 -targeting short hairpin RNAs (shRNAs) were tested for knockdown (KD) efficiency using TSA201 cells and reverse transcription-quantitative polymerase chain reaction. A dual-component suppression and replacement (SupRep) CALM gene therapy (CALM-SupRep) was created by cloning into a single construct CALM1 -, CALM2 -, and CALM3-specific shRNAs that produce KD (suppression) of each respective gene and a shRNA-immune CALM1 cDNA (replacement). CALM1-F142L, CALM2-D130G, and CALM3-D130G induced pluripotent stem cell-derived CMs were generated from patients with CaM-mediated long-QT syndrome. A voltage-sensing dye was used to measure action potential duration at 90% repolarization (APD90)., Results: Following shRNA KD efficiency testing, a candidate shRNA was identified for CALM1 (86% KD), CALM2 (71% KD), and CALM3 (94% KD). The APD90 was significantly prolonged in CALM2-D130G (647±9 ms) compared with CALM2-WT (359±12 ms; P <0.0001). Transfection with CALM -SupRep shortened the average APD90 of CALM2-D130G to 457±19 ms (66% attenuation; P <0.0001). Additionally, transfection with CALM -SupRep shortened the APD90 of CALM1-F142L (665±9 to 410±15 ms; P <0.0001) and CALM3-D130G (978±81 to 446±6 ms; P <0.001)., Conclusions: We provide the first proof-of-principle suppression-replacement gene therapy for CaM-mediated long-QT syndrome. The CALM-SupRep gene therapy shortened the pathologically prolonged APD90 in CALM1 -, CALM2 -, and CALM3-variant CaM-mediated long-QT syndrome induced pluripotent stem cell-derived CM lines. The single CALM-SupRep construct may be able to treat all calmodulinopathies, regardless of which of the 3 CaM-encoding genes are affected., Competing Interests: Dr Ackerman is a consultant for Abbott, Boston Scientific, Bristol Myers Squibb, Daiichi Sankyo, Invitae, Medtronic, Tenaya Therapeutics, and UpToDate. Dr Ackerman and Mayo Clinic are involved in an equity/royalty relationship with AliveCor, Anumana, ARMGO Pharma, Pfizer, and Thryv Therapeutics. However, none of these entities have contributed to this study in any manner. The other authors report no conflicts.

Objective: To describe our early observations with sudden cardiac arrest (SCA) and sudden death (SD) in patients using vape products., Patients and Methods: A retrospective analysis of Mayo Clinic's Windland Smith Rice Genetic Heart Rhythm Clinic and Sudden Death Genomics Laboratory was performed on all SCA survivors and decedents who presented between January 1, 2007, and December 31, 2021, to identify patients/decedents with a history of vaping. Data abstraction included patient demographics, clinical characteristics, and documented use of vape products., Results: Among 144 SCA survivors and 360 SD victims, there were six individuals (1%; 3 females) with unexplained SCA (n=4) or SD (n=2) that was temporally associated with vaping use with a mean age at sentinel event of 23±5 years. The SCA survivors include a 19-year-old male who was resuscitated from documented ventricular fibrillation 40 minutes after vaping and a 19-year-old male who was resuscitated from ventricular fibrillation a few hours post vaping. The first SD victim was a 19-year-old female with exercise-induced asthma who died in her sleep after vaping that evening. Autopsy results showed eosinophilic infiltrates in the lung tissue and death was attributed to bronchial asthma. The second vaping-associated death involved a 26-year-old male whose autopsy attributed the death to acute respiratory distress syndrome., Conclusion: We have identified six young individuals with a history of vaping who experienced a near fatal episode or a tragic SD. Although larger cohort studies are needed to quantify the actual risk of SD, it seems prudent to sound an early warning about vaping's potential lethality., (Copyright © 2023 Mayo Foundation for Medical Education and Research. Published by Elsevier Inc. All rights reserved.)

Hypertrophic cardiomyopathy (HCM) is a genetically heterogenous condition with about half of cases remaining genetically elusive or non-genetic in origin. HCM patients with a positive genetic test (HCM Sarc ) present earlier and with more severe disease than those with a negative genetic test (HCM Neg ). We hypothesized these differences may be due to and/or reflect proteomic and phosphoproteomic differences between the two groups. TMT-labeled mass spectrometry was performed on 15 HCM Sarc , 8 HCM Neg , and 7 control samples. There were 243 proteins differentially expressed and 257 proteins differentially phosphorylated between HCM Sarc and HCM Neg . About 90% of pathways altered between genotypes were in disease-related pathways and HCM Sarc showed enhanced proteomic and phosphoproteomic alterations in these pathways. Thus, we show HCM Sarc has enhanced proteomic and phosphoproteomic dysregulation observed which may contribute to the more severe disease phenotype., (© 2023. Springer Nature Limited.)

Background: Long QT syndrome type 2 (LQT2) is caused by pathogenic variants in KCNH2. LQT2 may manifest as QT prolongation on an electrocardiogram and present with arrhythmic syncope/seizures and sudden cardiac arrest/death. Progestin-based oral contraceptives may increase the risk of LQT2-triggered cardiac events in women. We previously reported on a woman with LQT2 and recurrent cardiac events temporally related and attributed to the progestin-based contraceptive medroxyprogesterone acetate ("Depo-Provera" [Depo] MilliporeSigma, Catalog# 1378001, St. Louis, MO)., Objective: The purpose of this study was to evaluate the arrhythmic risk of Depo in a patient-specific induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) model of LQT2., Methods: An iPSC-CM line was generated from a 40-year-old woman with p.G1006Afs∗49-KCNH2. A CRISPR/Cas9 gene-edited/variant-corrected isogenic control iPSC-CM line was generated. FluoVolt (Invitrogen, F10488, Waltham, MA) was used to measure the action potential duration after treatment with 10 μM Depo. Erratic beating patterns characterized as alternating spike amplitudes, alternans, or early afterdepolarization-like phenomena were assessed using multielectrode array (MEA) after 10 μM Depo, 1 μM isoproterenol (ISO), or combined Depo + ISO treatment., Results: Depo treatment shortened the action potential duration at 90% repolarization of G1006Afs∗49 iPSC-CMs from 394 ± 10 to 303 ± 10 ms (P < .0001). Combined Depo + ISO treatment increased the percentage of electrodes displaying erratic beating in G1006Afs∗49 iPSC-CMs (baseline: 18% ± 5% vs Depo + ISO: 54% ± 5%; P < .0001) but not in isogenic control iPSC-CMs (baseline: 0% ± 0% vs Depo + ISO: 10% ± 3%; P = .9659)., Conclusion: This cell study provides a potential mechanism for the patient's clinically documented Depo-associated episodes of recurrent ventricular fibrillation. This in vitro data should prompt a large-scale clinical assessment of Depo's potential proarrhythmic effect in women with LQT2., (Copyright © 2023 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Triadin knockout syndrome (TKOS) is a malignant arrhythmia disorder caused by recessive null variants in TRDN-encoded cardiac triadin. Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were generated from two unrelated TKOS patients and an unrelated control. CRISPR-Cas9 gene editing was used to insert homozygous TRDN-p.D18fs ∗ 13 into a control line to generate a TKOS model (TRDN -/- ). Western blot confirmed total knockout of triadin in patient-specific and TRDN -/- iPSC-CMs. iPSC-CMs from both patients revealed a prolonged action potential duration (APD) at 90% repolarization, and this was normalized by protein replacement of triadin. APD prolongation was confirmed in TRDN -/- iPSC-CMs. TRDN -/- iPSC-CMs revealed that loss of triadin underlies decreased expression and co-localization of key calcium handling proteins, slow and decreased calcium release from the sarcoplasmic reticulum, and slow inactivation of the L-type calcium channel leading to frequent cellular arrhythmias, including early and delayed afterdepolarizations and APD alternans., Competing Interests: Conflict of interests M.J.A. is a consultant for Abbott, ARMGO Pharma, Boston Scientific, Daiichi Sankyo, Invitae, LQT Therapeutics, Medtronic, and UpToDate. M.J.A. and Mayo Clinic are involved in equity/royalty relationships with AliveCor and Anumana. These relationships are all modest, and none of these entities have contributed to this study in any manner., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Background: Pathogenic variants in the SCN5A-encoded Nav1.5 sodium channel cause type 3 long QT syndrome (LQT3). We present the case of an infant with severe LQT3 who was refractory to multiple pharmacologic therapies as well as bilateral stellate ganglionectomy. The patient's novel variant, p.F1760C-SCN5A, involves a critical residue of the Nav1.5's local anesthetic binding domain., Objective: The purpose of this study was to characterize functionally the p.F1760C-SCN5A variant using TSA-201 and patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs)., Methods: Whole-cell patch clamp was used to assess p.F1760C-SCN5A associated sodium currents with/without lidocaine (Lido), flecainide, and phenytoin (PHT) in TSA-201 cells. p.F1760C-SCN5A and CRISPR-Cas9 variant-corrected isogenic control (IC) iPSC-CMs were generated. FluoVolt voltage dye was used to measure the action potential duration (APD) with/without mexiletine or PHT., Results: V 1/2 of inactivation was right-shifted significantly in F1760C cells (-72.2 ± 0.7 mV) compared to wild-type (WT) cells (-86.3 ± 0.9 mV; P <.0001) resulting in a marked increase in window current. F1760C increased sodium late current 2-fold from 0.18% ± 0.04% of peak in WT to 0.49% ± 0.07% of peak in F1760C (P = .0005). Baseline APD to 90% repolarization (APD 90 ) was increased markedly in F1760C iPSC-CMs (601 ± 4 ms) compared to IC iPSC-CMs (423 ± 15 ms; P <.0001). However, 4-hour treatment with 10 μM mexiletine failed to shorten APD 90 , and treatment with 5μM PHT significantly decreased APD 90 of F1760C iPSC-CMs (453 ± 6 ms; P <.0001)., Conclusion: PHT rescued electrophysiological phenotype and APD of a novel p.F1760C-SCN5A variant. The antiepileptic drug PHT may be an effective alternative therapeutic for the treatment of LQT3, especially for variants that disrupt the Lido/mexiletine binding site., (Copyright © 2023 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)