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Background Clinical trials can be logistically burdensome, financially expensive, and potentially detrimental to patient outcomes. The NeoSphere study, which investigated the efficacy of docetaxel (T), pertuzumab (P), and trastuzumab (H) in combination with one another, was performed recently over an eight year stretch with n=254 operable breast cancer patients distributed across four study arms. Given the inherent hurdles of clinical trials, we set out to replicate the NeoSphere Trial in silico. We posit that never-before-possible in silico clinical trials can accurately forecast regimen efficacy/pathological complete response (pCR) rates and expand insights well in advance of human clinical trials. Analysis of tumor microenvironment and chemical interactions therein can enable drug developers to garnish more comprehensive insights than ex vivo or in vitro techniques. We aim to comprehensively understand cancer by leveraging our commercially available biophysical modeling platform and using all major hallmarks of cancer variation as input. Methods Selecting from the SimBioSys Virtual TumorBank of 3000+ past patient breast tumors and accompanying standard of care (SoC) clinical data, we matched NeoSphere sample composition based on age, tumor/node stage, cancer subtype, and HER2 receptor status. This generated a sample of n=144 patients, which were included across all four study arms (TH, THP, HP, and TP). Drug models used in our simulations were derived from publicly available data. Our main outcomes of interest (in operable breast cancer) included pCR rate by treatment arm, and pCR by treatment arm stratified by hormone receptor (HR) status (+/-). pCR was assessed per patient based on final simulation volume threshold of 0.1cc. Parameters from the NeoSphere study were mirrored in our SimBioSys Virtual Trial where possible, including treatment time, and time to surgery. We did not simulate post-surgery treatment. pCR rates were compared between virtual and clinical trials using two-tailed Fisher’s Exact tests. Results In non-stratified analyses, we observed pCR rates of 20.1% (TH), 42.4% (THP), 2.8% (HP), and 20.8% (TP) per arm, compared to 23.4% (TH), 47.7% (THP), 16.9% (HP), and 26.7% (TP) in the NeoSphere trial. Our non-stratified results were not significantly different from NeoSphere in the TH (p=0.72, OR=0.86), THP (p=0.69, OR=0.89) or TP (p=0.48, OR=0.78) arms. In our HP arm, we observed lower pCR rates (p=0.002, OR=0.17) than NeoSphere. Importantly, we predicted disease progression in 8.3% of HP patients, closely mirroring NeoSphere HP disease progression (7.4%). In our HR+ analyses, none of our results from the TH, THP, HP, or TP arms were significantly different than NeoSphere (prange = 0.34 to 0.69, ORrange = 0.61 to 1.36). In our HR- analyses, our results were not significantly different from NeoSphere in the TH (p=1.00, OR=1.03), THP (p=0.87, OR=0.92) or TP (p=0.55, OR=1.33) trial arms. However, as in our non-stratified analysis, in our HR-negative sample we observed a significantly lower proportion of pCR in patients treated with HP than in NeoSphere (p=0.0003, OR=0.00). Conclusion Using bleeding-edge biophysical simulations, our never-before-possible in silico clinical trial retrospectively predicted regimen efficacy, pCR rate, and disease progression of the NeoSphere clinical trial. Currently, we are investigating the impact of drug delivery, drug sensitivity, metabolism, and spatial heterogeneity on tumor responses within our trial. In the near future, our virtual clinical trials will curtail the negative aspects of real-world clinical trials, while enabling drug developers to garnish more comprehensive insights than ex vivo or in vitro techniques. Citation Format: John Ryan Pfeiffer, Tim Foley, Eduardo Braun, Anu Antony. Virtual replication of the NeoSphere trial using SimBioSys TumorScope: Associating standard of care data with clinical outcomes in HER2 positive breast cancer patients to garnish novel insights in silico [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-08-02.

Cardiac arrhythmias are responsible for 200-300 thousand deaths/year. Despite considerable research effort, much remains to be elucidated concerning the underlying mechanisms of arrhythmogenesis. Mutations in transient receptor potential melastatin 4 (TRPM4), a widely expressed Ca 2+ -activated nonselective cation channel, have been associated with causing cardiac arrhythmias. However, direct genotype-phenotype correlation of arrhythmogenic TRPM4 mutant variants are often complicated, as this channel is not primary to the cardiac action potential. Here, we assessed the electrophysiological and post-transcriptional molecular properties of a single mutation (R892C)-TRPM4 associated with short QT syndrome (SQTS) and a triple mutation (R250C|A432T|G582S)-TRPM4 associated with long QT syndrome (LQTS), using stably transfected HEK293 cells. Overall, protein expression of the triple mutant was found to be significantly reduced, with increased proteasomal degradation, but enhanced SUMOylation, as compared to either WT or the single R892 mutant TRPM4 channel. Consequently, expression of R250C|A432T|G582S-TRPM4 was significantly lower at the cellular membrane than either R892C- and WT-TRPM4. In contrast, while total expression of TRPM4 was not significantly different between WT and the R892C single mutant, although the R892C exhibited increase aggregation. Patch-clamp cellular electrophysiology experiments indicated that both single and triple TRPM4 mutant channels could be activated by lower Ca 2+ concentrations compared to WT. However, R892C-TRPM4 channels inactivated faster, while R250C|A432T|G582S-TRPM4 channels inactivated much slower compared to WT. These data as obtained in our homologous recombinant overexpression system reveal that while the R892C-TRPM4 mutant variant exhibited normal-to-higher levels of expression and increased Ca 2+ -activation sensitivity, its tendency to aggregate combined with faster inactivation can result in overall loss-of-function compared to WT, correlative with SQTS. Conversely, while the R250C|A432T|G582S-TRPM4 mutant variant exhibited reduced expression and perturbed trafficking, its increased Ca 2+ -activation sensitivity and slow inactivation can result in overall gain-of-function compared to WT, correlative with LQTS.

Background. We report an inherited cardiac arrhythmia syndrome consisting of Brugada and Early Repolarization Syndrome associated with variants in SCN9A, PXDNL, and FKBP1B. the proband inherited the 3 mutations and exhibited palpitations and arrhythmia-mediated syncope, whereas the parents and sister, who carried one or two of the mutations, were asymptomatic. Methods and Results. We assessed the functional impact of these mutations in induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) derived from the proband and an unaffected family member. Current and voltage clamp recordings, as well as confocal microscopy analysis of Ca2+ transients, were evaluated in hiPSC-CMs from the proband and compared these results with hiPSC-CMs from undiseased controls. Genetic analysis using next-generation DNA sequencing revealed heterozygous mutations in SCN9A, PXDNL, and FKBP1B in the proband. the proband displayed right bundle branch block and exhibited episodes of syncope. the father carried a mutation in FKBP1B, whereas the mother and sister carried the SCN9A mutation. None of the 3 family members screened developed cardiac events. Action potential recordings from control hiPSC-CM showed spontaneous activity and a low upstroke velocity. in contrast, the hiPSC-CM from the proband showed irregular spontaneous activity. Confocal microscopy of the hiPSC-CM of the proband revealed low fluorescence intensity Ca2+ transients that were episodic in nature. Patch-clamp measurements in hiPSC-CM showed no difference in I-Na but reduced ICa in the proband compared with control. Coexpression of PXDNL-R391Q with SCN5A-WT displayed lower I-Na density compared to PXDNLWT. in addition, coexpression of PXDNL-R391Q with KCND3-WT displayed significantly higher I-to density compared to PXDNL-WT. Conclusion. SCN9A, PXDNL, and FKBP1B variants appeared to alter spontaneous activity in hiPSC-CM. Only the proband carrying all 3 mutations displayed the ERS/BrS phenotype, whereas one nor two mutations alone did not produce the clinical phenotype. Our results suggest a polygenic cause of the BrS/ERS arrhythmic phenotype due to mutations in these three gene variants caused a very significant loss of function of I-Na and I-Ca and gain of function of I-to., NHLBIUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USANIH National Heart Lung & Blood Institute (NHLBI) [HL47678, HL138103, HL152201]; Martha and Wistar Morris Fund; W/W. Smith Trust; National Natural Science Foundation Project of ChinaNational Natural Science Foundation of China (NSFC) [81670304]; Free and Accepted Mason of New York; Free and Accepted Mason of Florida; Free and Accepted Mason of Massachusetts; Free and Accepted Mason of Connecticut; Free and Accepted Mason of Maryland; Free and Accepted Mason of Wisconsin; Free and Accepted Mason of Washington; Free and Accepted Mason of Rhode Island; [HL145530-01A1], Drs. Antzelevitch and Barajas acknowledge support from NHLBI (HL47678, HL138103, and HL152201), the Martha and Wistar Morris Fund, and the W/W. Smith Trust. Dr. Hu acknowledges support by the National Natural Science Foundation Project of China (Grant no. 81670304), distinguished professor of Chutian Scholar Program of Hubei Province. Dr. Cordeiro acknowledges support from HL145530-01A1 and the Free and Accepted Masons of New York, Florida, Massachusetts, Connecticut, Maryland, Wisconsin, Washington, and Rhode Island.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are used for genetic models of cardiac diseases. We report an arrhythmia syndrome consisting of Early Repolarization Syndrome (ERS) and Short QT Syndrome (SQTS). The index patient (MMRL1215) developed arrhythmia-mediated syncope after electrocution and was found to carry six mutations. Functional alterations resulting from these mutations were examined in patient-derived hiPSC-CMs. Electrophysiological recordings were made in hiPSC-CMs from MMRL1215 and healthy controls. ECG analysis of the index patient showed slurring of the QRS complex and QTc = 326 ms. Action potential (AP) recordings from MMRL1215 myocytes showed slower spontaneous activity and AP duration was shorter. Field potential recordings from MMRL1215 hiPSC-CMs lack a “pseudo” QRS complex suggesting reduced inward current(s). Voltage clamp analysis of ICa showed no difference in the magnitude of current. Measurements of INa reveal a 60% reduction in INa density in MMRL1215 hiPSC-CMs. Steady inactivation and recovery of INa was unaffected. mRNA analysis revealed ANK2 and SCN5A are significantly reduced in hiPSC-CM derived from MMRL1215, consistent with electrophysiological recordings. The polygenic cause of ERS/SQTS phenotype is likely due to a loss of INa due to a mutation in PKP2 coupled with and a gain of function in IK,ATP due to a mutation in ABCC9.

Background: Brugada syndrome (BrS) is a severe inherited arrhythmia syndrome which can be unmasked by fever. Methods: A clinical analysis was performed in 134 probands diagnosed with fever-induced BrS, including 59 patients who received next-generation genetic sequencing. We employed a biophysics-based computational protocol to investigate whether protein structure destabilization contributes to Nav1.5 variant-mediated fever-induced BrS. Findings: Among all cases enrolled, the symptoms at diagnosis were syncope in 26 (19.40%) and major arrhythmic events (MAE) in 16 (11.94%). SCN5A variant carriers were significantly younger than probands free of SCN5A variants. Compared with a historical cohort of non-fever BrS probands carrying SCN5A variants, carriers with fever-induced BrS were prone to MAE at younger age, and had a higher proportion of variants localizing at the interdomain linkers. Modeling result showed that most variants are destabilizing when temperature increases, suggesting that Nav1.5 structure destabilization is the cause of fever-induced BrS associated with SCN5A variants. Interpretation: In our cohort, SCN5A variant carriers with fever-induced BrS present at a younger age and harbor SCN5A variants predominantly localized to interdomain linker regions of Nav1.5. These SCN5A variants typically induce destabilization of Nav1.5 structure at higher body temperatures. Patients with SCN5A mutations present within interdomain linker regions may warrant more aggressive monitoring and management of fever. Funding Statement: The current work was supported by the National Natural Science Foundation Project of China (Grant No. 81670304); the National Institutes of Health of USA (NIH R56 - HL47678], NIH R01 [HL138103]), NIH R01 [HL152201], the W.W. Smith Charitable Trust and the Wistar and Martha Morris Fund. Declaration of Interests: The authors report no relationships that could be construed as a conflict of interest. Ethics Approval Statement: This study was approved by the Institutional Review Board of each hospital and performed in accordance with the declaration of Helsinki. All participants gave written informed consent.

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 −8 ) near NOS1AP , KCNQ1 , and KLF12 , and 1 missense variant in KCNE1 (p.Asp85Asn) at the suggestive threshold ( P −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 (r g =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 P 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.

Objectives This study sought to evaluate the phenotypic and functional expression of an apparent hotspot mutation associated with short QT syndrome (SQTS). Background SQTS is a rare channelopathy associated with a high risk of life-threatening arrhythmias and sudden cardiac death (SCD). Methods Probands diagnosed with SQTS and their family members were evaluated clinically and genetically. KCNH2 wild-type (WT) and mutant genes were transiently expressed in HEK293 cells, and currents were recorded using whole-cell patch clamp and action potential (AP) clamp techniques. Results KCNH2 -T618I was identified in 18 members of 7 unrelated families (10 men; median age: 24.0 years). All carriers showed 100% penetrance with variable expressivity. Eighteen members in 7 families had SCD. The average QTc intervals of probands and all carriers was 294.1 ± 23.8 ms and 313.2 ± 23.8 ms, respectively. Seven carriers received an implantable cardioverter-defibrillator. Quinidine with adequate plasma levels was effective in prolonging QTc intervals among 5 cases, but 3 cases still had premature ventricular contraction or nonsustained ventricular tachycardia. Bepridil successfully prevented drug-refractory ventricular fibrillation in 1 case with 19-ms prolongation of the QTc interval. Functional studies with KCNE2 revealed a significant increase of I Kr (rapidly activating delayed rectifier potassium channel) tail-current density in homozygous (119.0%) and heterozygous (74.6%) expression compared with WT. AP clamp recordings showed I Kr was larger, and peak repolarizing current occurred earlier in mutant versus WT channels. Conclusions We reported the clinical characteristics and biophysical properties of the highly frequent mutation that contributes to genetically identified SQTS probands. These findings extend our understanding of the spectrum of KCNH2 channel defects in SQTS.

Introduction: Cardiac arrhythmias are generally associated with abnormal mutations in ion channel genes. Epilepsy is a disorder of neuronal function, which also involves abnormal channel function. Our Hypothesis: now increasing by demonstration that the etiologies of Brugada syndrome (BrS) and epilepsy may partly overlap. However, only a few genetic studies have addressed a possible link between cardiac and neural channelopathies. Methods: The suspected case and family were underwent thorough medical examination. Fifteen candidate genes were screened for ion channels by direct sequencing. Ion channel variants were cloned by site-directed mutagenesis and studied using patch clamp and confocal microscopy techniques in TSA201 cells. Results: A 36 y/o male with epilepsy showing typical type 1 Brugada pattern ECG during flecainide challenge test and under antiepileptic medication (valproic acid). Cardiac evaluation included a normal echocardiogram and exercise stress test. We identified two mutations (D2130N and A1717G) in CACNA1C and one in KCNE2 (T10M). All mutations are highly conserved. The variants in CACNA1C were located in C terminal and the one in KCNE2 was in N terminal. Functional studies in CACNA1C mutants were co-expressed with CACNB2b and CACNA2D1 . At 0 mV, peak ICa densities were reduced by 85% and 70% in D2130N and A1717G vs. WT respectively. Significant kinetic alterations included a negative shift in V1/2 of inactivation, and positive shift in V1/2 of activation, for D2130N and A1717G, respectively. Confocal study showed D2130N and A1717G conjugated to YFP trafficked normally to the cell membrane. We found a gain-of-function in Ito current when T10M- KCNE2 was co-expressed with KCND3 channels by 55% relative to WT. Conclusion: Our results suggest for the first time that several mutations in CACNA1C leads to a loss of function in ICa and thus can contribute to the development of BrS phenotype. T10M- KCNE2 produces a gain of function in Ito, which further aggravates BrS. Meanwhile, as previously reported, T10M- KCNE2 also produces a loss-of-function of IKr, so it is reasonable to deduce that the mutation is probably responsible for the epilepsy. It once again provides the evidence that anti-epilepsy drug could unmask potential Brugada ECG.

Introduction: Mutations in genes encoding the α ( KCND3) and β ( KCNE3 ) subunits of genes encoding the cardiac transient outward potassium (Ito) have been associated with inherited cardiac arrhythmia syndromes such as Brugada Syndrome (BrS) and Sudden Infant Death Syndromes (SIDS). Hypothesis: Novel genetic variant in DPP10 associated with severe pediatric J Wave Syndrome (JWS), IVF and SIDS. Methods: The proband, a 16 year-old female, presented with atrial fibrillation and atrial septal defect. Subsequently she developed accentuated J waves in all ECG leads leading to repeated episodes of VT/VF (Type 3 ERS). Cilostazol proved effective in quieting VT/VF. She died of an electrical storm at 21 years of old. Genetic screening using Next Gen and Sanger methods uncovered a genetic variant in DPP10 but no variants in any other JWS susceptibility genes. Results: Transversion of thymine for guanine at nucleotide 15 predicted substitution of aspartic acid (D) for glutamine acid (E) at position 5 in exon 1b in the N-terminal of DPP10 (E5D) . The variation E5D was present in 5 unrelated patients with ERS (2), IVF (1) and BrS (3). E5D is highly conserved among species. Wild type (WT) and mutant genes were expressed in TSA201 cells and studied using whole-cell patch-clamp techniques at 37°C. Co-expression of KCND3 + KChIP2 + DPP10 /E5D generated Kv4.3 current density (I to ) 169.9% and 70.6% greater compared with KCND3 + KChIP2 + DPP10 /WT when homozygously and heterozygously expressed, respectively (n=9-12, pto by approximately 50% at +20 mV in E5D channels but less so (20 %) in WT channels. Conclusions: Our results provide, for the first time, evidence in support for the hypothesis that DDP10 is a novel susceptibility gene for life threatening arrhythmias associated with JWS. Our data suggest that DPP10- E5D contributes to the generation of a pathogenic substrate by boosting Ito and that Quinidine and Cilostazol serve as therapeutic options in this setting by reducing I to .

Background Phenotypic overlap of type 3 long QT syndrome ( LQT 3), Brugada syndrome (BrS), cardiac conduction disease ( CCD ), and sinus node dysfunction ( SND ) is observed with SCN 5A mutations. SCN 5A ‐E1784K is the most common mutation associated with BrS and LQTS 3. The present study examines the genotype–phenotype relationship in a large family carrying SCN 5A ‐E1784K and SCN 5A ‐H558R polymorphism. Methods and Results Clinical work‐up, follow‐up, and genetic analysis were performed in 35 family members. Seventeen were SCN 5A ‐E1784K positive. They also displayed QT c prolongation, and either BrS, CCD , or both. One carrier exhibited SND . The presence of SCN 5A ‐H558R did not significantly alter the phenotype of SCN 5A ‐E1784K carriers. Fourteen SCN 5A ‐E1784K patients underwent implantable cardioverter‐defibrillator ( ICD ) implantation; 4 developed VF and received appropriate ICD shocks after 8±3 months of follow‐up. One patient without ICD also developed VF after 6.7 years. These 5 cases carried both SCN 5A ‐E1784K and SCN 5A ‐H558R. Functional characterization was achieved by expressing SCN 5A variants in TSA 201 cells. Peak (I Na,P ) or late (I Na,L ) sodium currents were recorded using whole‐cell patch‐clamp techniques. Co‐expression of SCN 5A ‐E1784K and SCN 5A ‐ WT reduced I Na,P to 70.03% of WT , shifted steady‐state inactivation by −11.03 mV, and increased I Na,L from 0.14% to 1.86% of I Na,P . Similar changes were observed when SCN 5A ‐E1784K was co‐expressed with SCN 5A ‐H558R. Conclusions We demonstrate a strong genotype‐phenotype correlation with complete penetrance for BrS, LQTS , or CCD in the largest family harboring SCN 5A ‐E1784K mutation described so far. Phenotype of LQTS is present during all decades of life, whereas CCD develops with increasing age. Phenotypic overlap may explain the high event rate in carriers.

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 (Nav1B) 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 (INa) 56.5% smaller compared to SCN5A/WT + SCN1Bb/WT (n = 11-12, P

Background. Mutations in the SCN5A gene have been linked to Brugada syndrome (BrS), conduction disease, Long QT syndrome (LQT3), atrial fibrillation (AF), and to pre- and neonatal ventricular arrhythmias. Objective. The objective of this study is to characterize a novel mutation in Nav1.5 found in a newborn with fetal chaotic atrial tachycardia, post-partum intraventricular conduction delay, and QT interval prolongation. Methods. Genomic DNA was isolated and all exons and intron borders of 15 ion-channel genes were sequenced, revealing a novel missense mutation (Q270K) in SCN5A. Nav1.5 wild type (WT) and Q270K were expressed in CHO-K1 with and without the Navβ1 subunit. Results. Patch-clamp analysis showed ∼40% reduction in peak sodium channel current (INa) density for Q270K compared with WT. Fast and slow decay of INa were significantly slower in Q270K. Steady-state activation and inactivation of Q270K channels were shifted to positive potentials, and window current was increased. The tetrodotoxin-sensitive late INa was increased almost 3-fold compared with WT channels. Ranolazine reduced late INa in WT and Q270K channels, while exerting minimal effects on peak INa. Conclusion. The Q270K mutation in SCN5A reduces peak INa while augmenting late INa, and may thus underlie the development of atrial tachycardia, intraventricular conduction delay, and QT interval prolongation in an infant.

Background L-type calcium channel (LTCC) mutations have been associated with Brugada syndrome (BrS), short QT (SQT) syndrome, and Timothy syndrome (LQT8). Little is known about the extent to which LTCC mutations contribute to the J-wave syndromes associated with sudden cardiac death. Objective The purpose of this study was to identify mutations in the α1, β2, and α2δ subunits of LTCC (Ca v 1.2) among 205 probands diagnosed with BrS, idiopathic ventricular fibrillation (IVF), and early repolarization syndrome (ERS). CACNA1C, CACNB2b , and CACNA2D1 genes of 162 probands with BrS and BrS+SQT, 19 with IVF, and 24 with ERS were screened by direct sequencing. Methods/Results Overall, 23 distinct mutations were identified. A total of 12.3%, 5.2%, and 16% of BrS/BrS+SQT, IVF, and ERS probands displayed mutations in α1, β2, and α2δ subunits of LTCC, respectively. When rare polymorphisms were included, the yield increased to 17.9%, 21%, and 29.1% for BrS/BrS+SQT, IVF, and ERS probands, respectively. Functional expression of two CACNA1C mutations associated with BrS and BrS+SQT led to loss of function in calcium channel current. BrS probands displaying a normal QTc had additional variations known to prolong the QT interval. Conclusion The study results indicate that mutations in the LTCCs are detected in a high percentage of probands with J-wave syndromes associated with inherited cardiac arrhythmias, suggesting that genetic screening of Ca v genes may be a valuable diagnostic tool in identifying individuals at risk. These results are the first to identify CACNA2D1 as a novel BrS susceptibility gene and CACNA1C, CACNB2 , and CACNA2D1 as possible novel ERS susceptibility genes.

Background— Brugada syndrome, characterized by ST-segment elevation in the right precordial ECG leads and the development of life-threatening ventricular arrhythmias, has been associated with mutations in 6 different genes. We identify and characterize a mutation in a new gene. Methods and Results— A 64-year-old white male displayed a type 1 ST-segment elevation in V1 and V2 during procainamide challenge. Polymerase chain reaction-based direct sequencing was performed using a candidate gene approach. A missense mutation (L10P) was detected in exon 1 of SCN3B , the β3 subunit of the cardiac sodium channel, but not in any other gene known to be associated with Brugada syndrome or in 296 controls. Wild-type (WT) and mutant genes were expressed in TSA201 cells and studied using whole-cell patch-clamp techniques. Coexpression of SCN5A /WT+ SCN1B /WT+ SCN3B /L10P resulted in an 82.6% decrease in peak sodium current density, accelerated inactivation, slowed reactivation, and a −9.6-mV shift of half-inactivation voltage compared with SCN5A /WT+ SCN1B /WT+ SCN3B /WT. Confocal microscopy revealed that SCN5A /WT channels tagged with green fluorescent protein are localized to the cell surface when coexpressed with WT SCN1B and SCN3B but remain trapped in intracellular organelles when coexpressed with SCN1B /WT and SCN3B /L10P. Western blot analysis confirmed the presence of Na V β3 in human ventricular myocardium. Conclusions— Our results provide support for the hypothesis that mutations in SCN3B can lead to loss of transport and functional expression of the hNa v 1.5 protein, leading to reduction in sodium channel current and clinical manifestation of a Brugada phenotype.

Recent studies have demonstrated an association between mutations in CACNA1c or CACNB2b and Brugada syndrome (BrS). Previously described mutations all caused a loss of function secondary to a reduction of peak calcium current (I(Ca)). We describe a novel CACNB2b mutation associated with BrS in which loss of function is caused by accelerated inactivation of I(Ca). The proband, a 32 year old male, displayed a Type I ST segment elevation in two right precordial ECG leads following a procainamide challenge. EP study was positive with induction of polymorphic VT/VF. Interrogation of implanted ICD revealed brief episodes of very rapid ventricular tachycardia. He was also diagnosed with vasovagal syncope. Genomic DNA was isolated from lymphocytes. All exons and intron borders of 15 ion channel genes were amplified and sequenced. The only mutation uncovered was a missense mutation (T11I) in CACNB2b. We expressed WT or T11I CACNB2b in TSA201 cells co-transfected with WT CACNA1c and CACNA2d. Patch clamp analysis showed no significant difference between WT and T11I in peak I(Ca) density, steady-state inactivation or recovery from inactivation. However, both fast and slow decays of I(Ca) were significantly faster in mutant channels between 0 and + 20 mV. Action potential voltage clamp experiments showed that total charge was reduced by almost half compared to WT. We report the first BrS mutation in CaCNB2b resulting in accelerated inactivation of L-type calcium channel current. Our results suggest that the faster current decay results in a loss-of-function responsible for the Brugada phenotype

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BackgroundGenetic defects in KCNJ8, encoding the Kir6.1 subunit of the ATP-sensitive K(+) channel (I(K-ATP)), have previously been associated with early repolarization (ERS) and Brugada (BrS) syndromes. Here we test the hypothesis that genetic variants in ABCC9, encoding the ATP-binding cassette transporter of IK-ATP (SUR2A), are also associated with both BrS and ERS.Methods and resultsDirect sequencing of all ERS/BrS susceptibility genes was performed on 150 probands and family members. Whole-cell and inside-out patch-clamp methods were used to characterize mutant channels expressed in TSA201-cells. Eight ABCC9 mutations were uncovered in 11 male BrS probands. Four probands, diagnosed with ERS, carried a highly-conserved mutation, V734I-ABCC9. Functional expression of the V734I variant yielded a Mg-ATP IC₅₀ that was 5-fold that of wild-type (WT). An 18-y/o male with global ERS inherited an SCN5A-E1784K mutation from his mother, who displayed long QT intervals, and S1402C-ABCC9 mutation from his father, who displayed an ER pattern. ABCC9-S1402C likewise caused a gain of function of IK-ATP with a shift of ATP IC₅₀ from 8.5 ± 2 mM to 13.4 ± 5 μM (p

Mutations in CACNA1C that increase current through the CaV1.2 L-type Ca2+ channel underlie rare forms of long QT syndrome (LQTS), and Timothy syndrome (TS). We identified a variant in CACNA1C in a male child of Filipino descent with arrhythmias and extracardiac features by candidate gene sequencing and performed functional expression studies to electrophysiologically characterize the effects of the variant on CaV1.2 channels. As a baby, the subject developed seizures and displayed developmental delays at 30 months of age. At age 5 years, he displayed a QTc of 520 ms and experienced recurrent VT. Physical exam at 17 years of age was notable for microcephaly, short stature, lower extremity weakness and atrophy with hyperreflexia, spastic diplegia, multiple dental caries and episodes of rhabdomyolysis. Candidate gene sequencing identified a G>C transversion at position 5731 of CACNA1C (rs374528680) predicting a glycine>arginine substitution at residue 1911 (p.G1911R) of CaV1.2. The allele frequency of this variant is 0.01 in Malays, but absent in 984 Caucasian alleles and in the 1000 genomes project. In electrophysiological analyses, the variant decreased voltage-dependent inactivation, thus causing a gain of function of CaV1.2. We also observed a negative shift of V1/2 of activation and positive shift of V1/2 of channel inactivation, resulting in an increase of the window current. Together, these suggest a gain-of-function effect on CaV1.2 and suggest increased susceptibility for arrhythmias in certain clinical settings. The p.G1911R variant was also identified in a case of sudden unexplained infant death (SUID), for which an increasing number of clinical observations have demonstrated can be associated with arrhythmogenic mutations in cardiac ion channels. In summary, the combined effects of the CACNA1C variant to diminish voltage-dependent inactivation of CaV1.2 and increase window current expand our appreciation of mechanisms by which a gain of function of CaV1.2 can contribute to QT prolongation. Published version

The short QT syndrome (SQTS) is a rare channelopathy associated with a high risk of life-threatening arrhythmias, sudden cardiac death (SCD) or sudden death (SD). This study sought to evaluate the phenotypic and functional expression of an apparent hotspot mutation associated with SQTS. Probands

Background— Brugada syndrome is a potentially serious channelopathy that usually presents in adulthood and has only rarely been described in infancy. In the absence of metabolic or structural cardiac disease, rapid ventricular tachycardia (>200 bpm) and primary cardiac conduction disease are uncommon in infancy. We hypothesized that infants having rapid ventricular tachycardia and conduction abnormalities and not having structural or metabolic pathogeneses were likely to have mutations in depolarizing current channels. Methods and Results— A retrospective review of all clinical materials from a single institution over a 9-year period from all infants Conclusions— Infants having rapid ventricular tachycardia and conduction abnormalities in the absence of structural or metabolic abnormalities are likely to have disease-causing mutations in cardiac depolarizing channels.

Long QT syndrome (LQTS) is an inherited disorder characterized by prolonged QT intervals and potentially life-threatening arrhythmias. Mutations in 12 different genes have been associated with LQTS. Here we describe a patient with LQTS who has a mutation in KCNQ1 as well as a polymorphism in KCNH2. The proband (MMRL0362), a 32-year-old female, exhibited multiple ventricular extrasystoles and one syncope. Her ECG (QT interval corrected for heart rate (QTc) = 518ms) showed an LQT2 morphology in leads V4–V6 and LQT1 morphology in leads V1–V2. Genomic DNA was isolated from lymphocytes. All exons and intron borders of 7 LQTS susceptibility genes were amplified and sequenced. Variations were detected predicting a novel missense mutation (V110I) in KCNQ1, as well as a common polymorphism in KCNH2 (K897T). We expressed wild-type (WT) or V110I Kv7.1 channels in CHO-K1 cells cotransfected with KCNE1 and performed patch-clamp analysis. In addition, WT or K897T Kv11.1 were also studied by patch clamp. Current–voltage (I-V) relations for V110I showed a significant reduction in both developing and tail current densities compared with WT at potentials >+20 mV (p < 0.05; n = 8 cells, each group), suggesting a reduction in IKs currents. K897T- Kv11.1 channels displayed a significantly reduced tail current density compared with WT-Kv11.1 at potentials >+10 mV. Interestingly, channel availability assessed using a triple-pulse protocol was slightly greater for K897T compared with WT (V0.5 = –53.1 ± 1.13 mV and –60.7 ± 1.15 mV for K897T and WT, respectively; p < 0.05). Comparison of the fully activated I-V revealed no difference in the rectification properties between WT and K897T channels. We report a patient with a loss-of-function mutation in KCNQ1 and a loss-of-function polymorphism in KCNH2. Our results suggest that a reduction of both IKr and IKs underlies the combined LQT1 and LQT2 phenotype observed in this patient.

Background Brugada syndrome (BrS) is a common heritable channelopathy. Mutations in the SCN5A -encoded sodium channel (BrS1) culminate in the most common genotype. Objective This study sought to perform a retrospective analysis of BrS databases from 9 centers that have each genotyped >100 unrelated cases of suspected BrS. Methods Mutational analysis of all 27 translated exons in SCN5A was performed. Mutation frequency, type, and localization were compared among cases and 1,300 ostensibly healthy volunteers including 649 white subjects and 651 nonwhite subjects (blacks, Asians, Hispanics, and others) that were genotyped previously. Results A total of 2,111 unrelated patients (78% male, mean age 39 ± 15 years) were referred for BrS genetic testing. Rare mutations/variants were more common among BrS cases than control subjects (438/2,111, 21% vs. 11/649, 1.7% white subjects and 31/651, 4.8% nonwhite subjects, respectively, P −53 ). The yield of BrS1 genetic testing ranged from 11% to 28% ( P = .0017). Overall, 293 distinct mutations were identified in SCN5A: 193 missense, 32 nonsense, 38 frameshift, 21 splice-site, and 9 in-frame deletions/insertions. The 4 most frequent BrS1-associated mutations were E1784K (14×), F861WfsX90 (11×), D356N (8×), and G1408R (7×). Most mutations localized to the transmembrane-spanning regions. Conclusion This international consortium of BrS genetic testing centers has added 200 new BrS1-associated mutations to the public domain. Overall, 21% of BrS probands have mutations in SCN5A compared to the 2% to 5% background rate of rare variants reported in healthy control subjects. Additional studies drawing on the data presented here may help further distinguish pathogenic mutations from similarly rare but otherwise innocuous ones found in cases.

Background: Ion channelopathies are responsible for a number of genetic cardiac arrhythmia syndromes. Recent work demonstrated an association between mutations in CACNA1c and CACNB2b, the genes that encode the α and β subunits of the L-type calcium channel, and the Brugada syndrome (BrS). The mutations previously described all caused a loss of function secondary to a major reduction in peak calcium channel current (I Ca ). In the present study we describe a novel CACNB2b mutation associated with BrS in which loss of function was caused by accelerated inactivation of I Ca . Methods and Results: The proband, a 32 yo male, displayed a saddleback ST segment elevation in the right precordial leads that converted to a coved-type ECG following a procainamide challenge. His EP study was positive with double extrastimuli inducing polymorphic VT/VF. He was also diagnosed with vasovagal syncope. Genomic DNA was isolated from blood lymphocytes. All exons and intron borders of 12 ion channel genes were amplified and sequenced. The only mutation uncovered was a missense mutation (T11I) in CACNB2b. The effect of this mutation was studied by expression of WT or T11I CACNB2b in TSA201 cells co-transfected with WT CANCA1c and CACNA2d. Patch clamp analysis showed no difference in I Ca density between WT and T11I (17.9±1.8 vs 22.5±4.3 pA/pF, respectively at +20mV). Similarly, steady-state inactivation and channel recovery was not different between WT and T11I mutant channels. However, both the fast and slow decay of I Ca produced by T11I mutant were significantly faster compared to WT at potentials between −10 to +30 mV, suggesting a reduction in depolarizing current during the course of an action potential. Application of action potential voltage clamp pulses confirmed that T11I total charge was reduced by 42±2.3% compared to WT (p Conclusion: We report the first Brugada syndrome mutation in CaCNB2b resulting in accelerated inactivation of the L-type calcium channel. The T11I mutation caused a faster decay of cardiac L-type calcium current but did not significantly alter the magnitude of the peak current. Our results suggest that a reduced total charge carried by I Ca during the plateau of the action potential predisposes to the Brugada phenotype.

Background— Cardiac ion channelopathies are responsible for an ever-increasing number and diversity of familial cardiac arrhythmia syndromes. We describe a new clinical entity that consists of an ST-segment elevation in the right precordial ECG leads, a shorter-than-normal QT interval, and a history of sudden cardiac death. Methods and Results— Eighty-two consecutive probands with Brugada syndrome were screened for ion channel gene mutations with direct sequencing. Site-directed mutagenesis was performed, and CHO-K1 cells were cotransfected with cDNAs encoding wild-type or mutant CACNB2b (Ca vβ2b ), CACNA2D1 (Ca vα2δ1 ), and CACNA1C tagged with enhanced yellow fluorescent protein (Ca v 1.2). Whole-cell patch-clamp studies were performed after 48 to 72 hours. Three probands displaying ST-segment elevation and corrected QT intervals ≤360 ms had mutations in genes encoding the cardiac L-type calcium channel. Corrected QT ranged from 330 to 370 ms among probands and clinically affected family members. Rate adaptation of QT interval was reduced. Quinidine normalized the QT interval and prevented stimulation-induced ventricular tachycardia. Genetic and heterologous expression studies revealed loss-of-function missense mutations in CACNA1C (A39V and G490R) and CACNB2 (S481L) encoding the α 1 - and β 2b -subunits of the L-type calcium channel. Confocal microscopy revealed a defect in trafficking of A39V Ca v 1.2 channels but normal trafficking of channels containing G490R Ca v 1.2 or S481L Ca vβ2b -subunits. Conclusions— This is the first report of loss-of-function mutations in genes encoding the cardiac L-type calcium channel to be associated with a familial sudden cardiac death syndrome in which a Brugada syndrome phenotype is combined with shorter-than-normal QT intervals.

Background Mutations in genes encoding the α ( KCND3 ) and β ( KCNE3 ) subunits of genes encoding the cardiac transient outward potassium (I to ) have been associated with inherited cardiac arrhythmia syndromes such as Brugada syndrome (BrS) and sudden infant death syndromes (SIDS). Here, we identify and characterize a novel genetic variant in DPP10 associated with severe pediatric J-wave syndrome (JWS) characterized by early repolarization syndrome (ERS). Methods and Results The proband, a 14-year-old female, presented with atrial fibrillation. At age 16 she developed accentuated J waves in all ECG leads and multiple episodes of polymorphic ventricular tachycardia/ventricular fibrillation (VT/VF; type 3 ERS), resulting in appropriate ICD shocks. Cilostazol proved effective in quieting VT/VF. She died of an electrical storm at age 21. Genetic screening using Next Gen and Sanger methods uncovered a genetic variant in DPP10 but no variants in any other JWS susceptibility genes. Transversion of thymine for guanine at nucleotide 15 predicted substitution of aspartic acid (D) for glutamine acid (E) at position 5 in exon 1b in the N-terminal of DPP10 . The variation was present in 5 of 448 ethnically matched healthy controls (1.1%). E5 is highly conserved among species. The E5D rare polymorphism was found in the proband's aunt who was asymptomatic but displayed ER pattern in select ECG leads. Wild-type (WT) and mutant genes were expressed in TSA201 cells and studied using whole-cell patch-clamp techniques at 37°C. Coexpression of KCND3 + KChIP2 + DPP10 /E5D generated Kv4.3 current density (I to ) 169.9% and 70.6% greater compared with KCND3 + KChIP2 + DPP10 /WT when homozygously and heterozygously expressed, respectively (n = 9–12, P to and recovery from inactivation was slower in E5D channels. Quinidine (5 μM) and cilostazol (5 μM) inhibited I to by approximately 50% at +20 mV in E5D channels but less so (20 %) in WT channels. Conclusions Our results provide, for the first time, evidence supporting the hypothesis that DDP10 is a novel susceptibility gene for life-threatening arrhythmias associated with ERS. Our data suggest that DPP10- E5D contributes to generation of a pathogenic substrate by boosting I to and that quinidine and cilostazol serve as therapeutic options in this setting by reducing I to .

Background Timothy syndrome (TS) is a rare congenital long QT syndrome (LQTS) associated with extracardiac manifestations including craniofacial dysmorphia and dental abnormalities. The locus for TS is CACNA1C , which encodes the Ca V 1.2 L-type Ca 2+ channel, for which canonical mutations lead to a decrease in voltage-dependent inactivation (VDI). However, a recent report of a patient with LQTS in isolation and a CACNA1C mutation that did not affect VDI raised the question whether altered VDI is necessary for extracardiac phenotypes. In a patient with a maternally inherited microdeletion with a chromosomal translocation who presented with LQTS and associated ventricular tachyarrhythmias (Figure A), a subset of TS phenotypes, and a skeletal myopathy not readily explained by the translocation, we sought to identify a causative mutation for the TS phenotypes. Methods A candidate gene approach identified a mutation in CACNA1C that was absent in the mother. We performed electrophysiologic studies on the mutant and characterized CACNA1C expression in skeletal muscle with a mouse CACNA1C reporter line. Results We identified a glycine to arginine mutation at position 1911 (G1911R) in Ca V 1.2. Functional studies revealed that G1911R increased Ca V 1.2 channel availability (Figures B and C) and decreased VDI (Figure D). The CACNA1C reporter mouse showed no Ca V 1.2 expression in skeletal muscle. Conclusions We describe a CACNA1C mutation that leads to a subset of TS phenotypes. In the context of a recently described CACNA1C mutation that does not affect VDI in an LQTS patient without extracardiac phenotypes, these data suggest that the extracardiac phenotypes seen in TS require effects on VDI.

Several studies have demonstrated an association between Brugada syndrome (BrS) and mutations in genes encoding ion channel subunits including SCN5A, CACNA1C, CACNB2b, SCN1B, and KCNE3. Mutations in SCN5A, encoding the voltage-gated sodium channel Nav1.5, represent the majority with greater than 293 mutations in SCN5A linked to the syndrome (Kapplinger et al, Heart Rhythm, In press 2009). We identified a missense mutation (G1408R) in SCN5A in a large BrS family. Intriguingly, this mutation had been reported earlier in two independent studies and has also shown to be associated with Sick Sinus Syndrome (SSS) and Cardiac Conduction Defect (CCD) (Kyndt et al, 2001; Benson et al, 2003). Nav1.5-G1408R channels heterologously expressed in CHO cells and studied using patch-clamp techniques failed to generate any sodium channel current (INa). Co-expression of the mutated channels with wild-type (WT) channels resulted in a 50% reduction of current amplitudes with no changes in kinetic properties when compared with WT channels. The residue resides in the DIII pore region and is conserved among species. We addressed the importance of this amino acid at position 1408 by replacing it with another small neutral amino acid (G1408A) and by substituting a negatively charged aspartic acid (G1408D). Our results show that substituting glycine with alanine retains WT behavior while exchange to the positively charged arginine (G1408R) or negatively charged aspartic acid leads to a complete loss-of-function. In conclusion, we describe a SCN5A mutation associated with BrS which results in a loss of function of INa important for action potential generation. Further, we show that the presence of a neutral hydrophobic amino acid at this position is crucial for normal channel function.

Introduction: Inherited loss of function mutations in SCN5A, the gene that encodes the α-subunit of the human cardiac sodium channel (hNav1.5), have been linked to overlapping syndromes including cardiac conduction disease (CCD) and Brugada syndrome (BrS). The mechanisms responsible for the development of one without the other are poorly understood.Methods: Direct sequencing analysis was performed in a family with CCD. Wild type (WT) and variant channels were co-expressed with CD8 cDNA in TSA201 cells for electrophysiological study. Green fluorescent protein (GFP)-fused WT or mutant SCN5A genes were used for confocal microscopy to assess channel trafficking.Results: A novel SCN5A missense mutation, P1008S, was identified in all family members displaying 1st degree AV block, but not in unaffected family members nor in 430 reference alleles. Peak P1008S current was 11.77% of WT (p