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Introduction: Early repolarization syndrome (ERS) is an inherited sudden cardiac death syndrome. Hypothesis: In this study we test the role of genetic variants in cardiac calcium channel genes in the pathogenesis of ERS and probes the underlying mechanisms. Methods: PCR-based next-generation sequencing was carried out using a targeted gene approach. Unrelated ERS probands carrying calcium channel variants were evaluated clinically and compared with matched healthy controls. Wild type (WT) and mutant CACNA1C genes were co-expressed with CACNB2b and CACNA2D1 in HEK293 cells and studied using whole-cell patch-clamp and confocal fluorescence microscope . Results: Among 104 ERS probands, 16 carried pathogenic variants in calcium channel genes (32.2±14.6 years old, 87.5% male). The symptoms at diagnosis included syncope (56.3%), ventricular tachycardia/fibrillation (VT/VF, 62.5%), sudden cardiac death (SCD, 56.3%). Three cases (18.8%) had a family history of SCD or syncope. Eight patients (50.0%) had a single calcium gene rare variant. The other half carried rare variants in other ERS susceptible genes. Compared with controls, the heart rate was slower (72.7±8.9 vs. 65.6±16.1 bpm), QTc interval was shorter (408.2±21.4 vs. 386.8±16.9 ms) and Tp-e/QT was longer (0.22±0.05 vs.0.28±0.04) in calcium mutation carriers. Electrophysiological analysis of one mutation, CACNA1C -P817S revealed that the density of I Ca was reduced by approximately 84.6% compared to WT (-3.1±2.5 vs. -20.5±3.6 pA/pF, n=11 and 15, respectively). Heterozygous expression of mutant channels was associated with a 51.3% reduction of I Ca . Steady-state inactivation was shifted to more negative potentials and significantly accelerated. Confocal microscopy revealed trafficking impairment of CACNA1C -P817S (peripheral/central intensity: 0.94±0.1 in WT vs. 0.33±0.1 in P817S, n=10 and 9, respectively). Conclusions: ERS associated with loss of function (LOF) genetic defects in genes encoding the cardiac calcium channel represents a unique clinical entity characterized by decreased heart rate and QTc, as well as increased transmural dispersion of repolarization. In the case of CACNA1C -P817S impaired trafficking of the channel to the membrane contributes to the LOF.

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.

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.