Seiko Ohno

SCN5A-E1784K (c.5350G>A) is the most common variant associated with the long QT (LQTS) and Brugada syndromes (BrS). It can manifest variably as LQTS, BrS and/or conduction disorders. This presents a challenge for risk stratification. We aimed to describe clinical and ECG characteristics and identify risk markers that associate with arrhythmic events. We undertook a retrospective observational multicentre study of a large cohort of 231 subjects with SCN5A-E1784K from Europe, USA and Japan. Comprehensive demographic and clinical data, including initial presentation ECG and follow-up, were collected. ‘Lethal events’ were defined as sudden death, non-fatal cardiac arrest, and documented sustained VT or VF. ‘Cardiac events’ were defined as arrhythmic syncope plus any lethal events. Clinical characteristics and ECG parameters corrected for age were investigated for association with lethal and/or cardiac events. Fourteen (6%) subjects experienced a lethal event and 45 (19%) a cardiac event. PR interval and QRS duration were associated with lethal and cardiac events. In multivariable models, both PR interval and QRS duration were associated with lethal events but only QRS duration was associated with cardiac events. Only age-corrected QRS (rQRS) was associated with lethal and cardiac event-free survival from birth after correction for multiple testing. Ventricular myocardial conduction appears likely to play a role in the risk of arrhythmic events in patients with SCN5A-E1784K. This provides an important opportunity for the personalisation of management and has the potential to guide preventative therapies.

Fabry disease is a rare, X-linked lysosomal storage disorder, leading to α-galactosidase A deficiency. The primary cardiac involvement is left ventricular hypertrophy, which can progress to left ventricular dysfunction, heart failure, and fatal arrhythmias. We present a diagnostically challenging case of advanced-stage cardiac Fabry disease with worsening left ventricular dysfunction without left ventricular hypertrophy. A 72-year-old woman with a family history of dilated cardiomyopathy was referred for regular follow-up. The initial electrocardiogram 14 years ago showed a shortened PQ interval minus the P wave interval and inverted T waves; however, left ventricular hypertrophy was not observed. Three years prior, echocardiography revealed inferolateral wall thinning, and computed tomography and magnetic resonance imaging confirmed fatty infiltration and transmural late gadolinium enhancement in the thinned inferolateral wall. Two years later, she was admitted for heart failure, with left ventricular ejection fraction decreasing to 29%. Owing to progressive left ventricular dysfunction and family history, comprehensive genetic testing was performed, identifying a pathogenic GLA variant c.902G>A (p.Arg301Gln) that confirmed Fabry disease. Enzyme replacement therapy was initiated. This case demonstrates that advanced-stage cardiac Fabry disease can progress to left ventricular dysfunction, wall thinning, and fibrosis in the absence of prior left ventricular hypertrophy. Electrocardiogram abnormalities and multimodal imaging findings, such as wall thinning, fatty infiltration, and late gadolinium enhancement, are key indicators of cardiac Fabry disease. This case emphasizes the importance of comprehensive evaluation for early diagnosis, including electrocardiography, echocardiography, computed tomography, and magnetic resonance imaging, even without left ventricular hypertrophy.

BACKGROUND: Pathogenic SCN5A variants are associated with inherited arrhythmias such as long-QT syndrome, Brugada syndrome, and sick sinus syndrome. While Na _v 1.5, an α-subunit of the cardiac sodium channel encoded by SCN5A , has been considered to function as a monomer, recent studies reveal that a reduction of sodium current in wild-type Na _v 1.5 can be caused by dimerization with loss-of-function mutated Na _v 1.5 through dominant-negative effects. However, the clinical significance of the dominant-negative effect remains unclear. METHOD: We genetically screened a family who presented with sick sinus syndrome and sudden cardiac death. Whole-cell patch-clamp study using HEK293 (human embryonic kidney) cells coexpressing wild-type and variant SCN5A was performed. Channel dimerization was assessed by coimmunoprecipitation and proximity ligation assays. Also, the effects of difopein, a high-affinity inhibitor of Na _v 1.5 interaction via 14-3-3 proteins, were evaluated. RESULTS: The proband carried compound heterozygous variants p.T1396P and p.G833R. The whole-cell mode patch-clamp techniques demonstrated that the p.T1396P showed a dominant-negative effect on the peak sodium currents (37% decrease in I _Na ) and altered gating properties (5.6-mV shift in steady-state inactivation) when expressed with wild-type SCN5A . These effects were abolished by difopein. p.G833R showed no dominant-negative or coupled gating effect but still formed dimers. The proband developed earlier and more severe bradycardia than the mother, who only carries p.T1396P, suggesting that loss of coupled gating effect contributed to the severe phenotype. CONCLUSIONS: Our findings suggest that coupled gating may be physiologically important for normal Na _v 1.5 function, and its loss can exacerbate disease severity.

Background: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited disease with a poor prognosis and no curative therapy. It may present as arrhythmogenic sudden cardiac death and inevitably progress to terminal heart failure due to the loss of contractile tissue. This study aimed to generate knock-in (KI) mice carrying the 2 genetic variants (DSG2 p.R292C and p.D494A) most frequently found in Japanese ARVC patients, characterize their cardiac phenotype, and compare the results with those of human ARVC.Methods and Results: Variants were introduced using CRISPR/Cas9 genome editing at the corresponding mouse locations: Dsg2 p.R297C (RC) and p.D499A (DA). Cardiac function, morphology, and electrophysiology were evaluated using echography, magnetic resonance imaging, and telemetry. Tissue and cardiomyocytes were examined histologically. All mice with the variants developed biventricular cardiac dysfunction after 8 weeks of age, and it progressed with age. There was a significant variability in phenotype expression. Mice with RC died suddenly at 9 weeks of age. Some homozygous RC mice showed arrhythmia and conduction abnormalities on telemetry. In both variants, staining of cardiac sections revealed significant fibrosis, and apoptosis was detected using the terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling assay.Conclusions: We generated a KI ARVC mouse model with significant similarities to human disease. This model could be used for the elucidation of pathogenesis and the development of optimal therapy for ARVC.

Background and Aims: Patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) are at risk for potentially life-threatening arrhythmic events (AEs) even while treated with β-blockers. The aim was to develop a model for individualized prediction of AEs in patients with RYR2-mediated CPVT on β-blocker monotherapy. Methods: The derivation and independent validation cohorts included 743 and 129 patients, respectively. AEs were defined as arrhythmic syncope, appropriate implantable cardioverter–defibrillator shock, sudden cardiac arrest (SCA), and sudden cardiac death. Near-fatal or fatal AEs (nf/fAEs) included all AEs except for arrhythmic syncope. Prediction models using Cox regression were developed and internally and externally validated. Results: A total of 102 (13.7%) patients in the derivation cohort and 24 (18.6%) patients in the validation cohort experienced ≥1 AE over a median follow-up of 5.1 [interquartile range (IQR), 7.7] and 2.4 (IQR, 4.4) years, respectively. Predictors of AE were arrhythmic syncope or SCA prior to diagnosis and age at β-blocker initiation. In the derivation and validation cohorts, the optimism-corrected C-indices of the models for AE were 0.67 [95% confidence interval (CI) 0.62–0.72] and 0.59 (95% CI 0.48–0.71), respectively. For nf/fAEs, ventricular arrhythmia severity before β-blocker initiation was a fourth independent predictor, and C-indices of the models in the derivation and validation cohorts were 0.74 (95% CI 0.68–0.80) and 0.60 (95% CI 0.47–0.72), respectively. In the derivation cohort, calibration slopes were 1.00 (95% CI 0.59–1.41) for AE and 1.00 (95% CI 0.69–1.32) for nf/fAE. Conclusions: These externally validated risk prediction models using clinical parameters accurately distinguished CPVT patients on β-blocker monotherapy at low and high risk for future AEs while treated with β-blockers. These models provide guidance for implementation of clinical management therapies to prevent AEs in patients with CPVT.

Sudden unexpected death in epilepsy (SUDEP) is one of the most frequent causes of death in patients with epilepsy, though the pathogenesis of SUDEP has not been well elucidated. Here, we report novel heterozygous KCND3 variants, p.V401L and p.V401M, identified in young patients with refractory epilepsy (RE) and neurodevelopmental disorders, and the functional properties of these variants. We aimed to investigate the electrophysiological changes in de novo KCND3 variants and analyse the pharmacological effects of quinidine on these variants. Chinese hamster ovary (CHO) cells were transiently co-transfected with wild-type (WT) and/or variant KCND3 and Kcnip2. Transient outward potassium currents (I_to) were recorded using the whole-cell patch-clamp method. The inhibitory effect of quinidine on I_to was evaluated. In electrophysiological analysis, CHO cells expressing the variant channels showed a significant increase in current density compared with those expressing WT channels. The I_to activation curves were shifted significantly to the left, and significantly slower inactivation time constants were observed in both variant channels. Recovery from inactivation of the variant channels was significantly slower than that of WT. Quinidine suppressed I_to in a concentration-dependent manner and accelerated the slow inactivation of variant channels. In conclusion, de novo KCND3 variants identified in patients with RE and neurodevelopmental disorders showed gain and loss of function effects on I_to. These patients may be at risk of developing early repolarization syndrome, leading to SUDEP. Increased I_to was suppressed by quinidine, suggesting that it may be an effective therapy for RE and possibly for preventing SUDEP.

Background: Pathogenic SCN5A variants are associated with inherited arrhythmias such as long QT syndrome, Brugada syndrome, and sick sinus syndrome (SSS). While Na _v 1.5, an α-subunit of the cardiac sodium channel encoded by SCN5A , has been considered to function as a monomer, recent studies reveal that a reduction of sodium current in wild-type (WT) Na _v 1.5 can be caused by dimerization with loss-of-function (LOF) mutated Na _v 1.5 through dominant-negative (DN) effects. However, the clinical significance of the DN effect remains unclear. Method: We genetically screened a family who presented with SSS and sudden cardiac death (SCD). Whole-cell patch-clamp study using HEK293 cells co-expressing WT- and variant SCN5A was performed. Channel dimerization was assessed by co-immunoprecipitation and proximity ligation assays. Also, the effects of difopein, a high affinity inhibitor of Na _v 1.5 interaction via 14-3-3 proteins, were evaluated. Results: The proband carried compound heterozygous variants p.T1396P and p.G833R. The whole-cell mode patch-clamp techniques demonstrated that the p.T1396P showed a DN effect on the peak sodium currents (37% decrease in I _Na ) and altered gating properties (+5.6 mV shift in steady-state inactivation) when expressed with WT SCN5A . These effects were abolished by difopein. p.G833R showed no DN or coupled gating effect but still formed dimers. The proband developed earlier and more severe bradycardia than her parent, who only carries p.T1396P, suggesting that loss of coupled gating effect contributed to the severe phenotype. Conclusion: Our findings suggest that coupled gating may be physiologically important for normal Na _v 1.5 function, and that its loss can exacerbate disease severity.