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A 10-year-old female patient experienced syncope while swimming, and electrocardiography revealed polymorphic ventricular tachycardia, leading to a diagnosis of catecholaminergic polymorphic ventricular tachycardia. No pathogenic variant was identified in RYR2. Additional comprehensive genetic testing revealed novel compound heterozygous variants in trans-2,3-enoyl-coenzyme A reductase–like gene, which caused a recessive form of catecholaminergic polymorphic ventricular tachycardia.

Background: Phenotypes often differ even within family members carrying the same SCN5A mutation. We aimed to evaluate the genetic modifiers in a family with Brugada syndrome (BrS) and sick sinus syndrome (SSS) with an SCN5A mutation that causes the truncated alpha-subunit of cardiac Na channel protein. Methods: To detect the genetic modifiers, we performed targeted panel sequencing of the coding region of 46 genes that are related to primary arrhythmia syndrome, by using a bench-top, next generation sequencer. Phenotype–genotype relationships were evaluated among the family members. Results: Index proband was a 13-year old (yo) boy with cardiac conduction defect as well as BrS. Genetic analysis revealed that he and his three asymptomatic family members carried a novel nonsense mutation: SCN5A-Q779X. Both genotype-positive mother and sister exhibited coved type ST elevation and his sister had SSS, whereas his elder brother exhibited saddleback type ST elevation induced by pilsicainide administration. We detected four non-synonymous variants (DSG2-R773K, SCN1B-L210P, -S248R, and -R250T) in the proband, his mother and his sister, but not in his brother. Conclusion: Phenotypic differences between the proband and his brother carrying the same nonsense SCN5A mutation could be explained by modifiers such as SCN1B, and DSG2 gene variants.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by degeneration of the right ventricle and ventricular tachycardia originating from the right ventricle. Additionally, the disease is an inherited cardiomyopathy that mainly follows the autosomal dominant pattern. More than 10 genes have been reported as causative genes for ARVC, and more than half of ARVC patients carry mutations in desmosome related genes. The desmosome is one of the structures involved in cell adhesion and its disruption leads to various diseases, including a skin disease called pemphigus. Among desmosome genes, mutations in PKP2 are most frequently identified in ARVC patients. Although the genotype–phenotype correlations remain to be fully studied, many studies have reported clinical manifestations of, prognosis for, and appropriate therapies for ARVC from the perspective of gene mutations. A collective review of these reports would enhance the understanding of ARVC pathogenesis and clinical manifestation. This review discusses the clinical issues of ARVC from the genetic background.

Background: The gene KCNE1 encodes the β-subunit of cardiac voltage-gated K+ channels and causes long QT syndrome (LQTS). LQTS is characterized by the prolongation of QT interval and lethal arrhythmias such as torsade de pointes (TdP). A KCNE1 polymorphism, D85N, has been shown to modify the phenotype of LQTS through a loss-of-function effect on both KCNQ1 and KCNH2 channels when co-expressed and reconstituted in a heterologous expression system. Methods: A screening for the D85N polymorphism was performed in 355 LQTS families with mutations in KCNQ1, KCNH2, or SCN5A. Among the probands who had a heterozygous status with the polymorphism, we focused on a family with a KCNH2 mutation (E58K), a N-terminal missense mutation, and examined the clinical significance of this polymorphism. We also conducted biophysical assays to analyze the effect of the polymorphism in mammalian cells. Results: In 355 probands, we found 14 probands (3.9%) who had a heterozygous compound status with the D85N polymorphism. In the family with a KCNE1-D85N polymorphism and a KCNH2-E58K mutation, the proband and her daughter carried both the KCNH2 mutation and the KCNE1-D85N polymorphism. They experienced repetitive syncope and TdP. Two sons of the proband had either KCNH2-E58K mutation or KCNE1-D85N, but were asymptomatic. Biophysical assays of KCNE1-D85N with KCNH2-E58K variants produced a larger reduction in the reconstituted IKr currents compared to co-expression with wild-type KCNE1. Conclusions: The KCNE1-D85N polymorphism modified the clinical features of LQTS patients.

Background: J-point elevation has been demonstrated to be associated with ventricular fibrillation (VF) and has been proposed as a cause of the J-wave syndrome (JWS). A mutation of KCNJ8, S422L, was reported as a culprit gene. This study aimed to determine the prevalence of KCNJ8 mutations in a Japanese population with JWS or idiopathic VF (IVF). Methods: A total of 230 probands with JWS and IVF underwent genetic screening of KCNJ8. To analyze and compare clinical and electrocardiographic characteristics, the probands were divided into 4 groups: Brugada (Br) pattern only, early repolarization (ER) pattern only, Br and ER patterns, and true IVF. Results: The results of the genetic analysis revealed no S422L or other KCNJ8 mutations and indicated no significant difference between the groups. Conclusion: The KCNJ8 mutation showed no association with JWS or IVF among our Japanese patients.

Brugada syndrome (BrS) is associated with the familial sudden death syndrome, and more than 10 genes have been reported as causative for or modifiers of BrS. All gene mutations are related to functional changes of inward sodium or calcium currents or outward potassium currents. SCN5A was the first gene known to be associated with BrS; it encodes the α-subunit of the cardiac sodium channel. Approximately 20% of BrS patients in genotyped cases were found to carry SCN5A mutations. The frequency for other BrS-associated gene mutations is so low that genotype–phenotype correlations for these genes have not been studied to the same extent as SCN5A-related BrS. In some families with SCN5A mutations, the penetrance of the mutations is low, and pathophysiological changes in the right ventricular outflow tract were reported in patients with SCN5A mutations. Furthermore, the phenotypes of SCN5A-related BrS can overlap with other phenotypes, including long QT and sick sinus syndrome, thereby suggesting that SCN5A mutations might be modifiers for BrS, but they do not direct cause BrS. Here, we summarize the genetic background of BrS, with a particular focus on recent progress in this field.

Background: β-blockers offer the first line therapy in congenital long QT syndrome (LQTS), and are more effective to prevent the cardiac event in LQTS type 1 than in type 2 or 3. In contrast, left cardiac sympathetic denervation (LCS D) was shown to be highly effective in patients refractory to β-blockers. Total sympathetic ablation by LCSD indicates the addititional involvement of α-adr enoceptor-mediated pathway. In genotyped LQT2 patients, we therefore hypothesized that blockade of α-adrenoceptor in addition to α-adrenoceptor by carvedilol could reduce cardiac events more efficiently than other types of β-blockers. Methods and Results: The study population consisted of 51 genotyped LQT2 patients (18 males, 23 ± 11years old). They were divided into 2 groups (group 1: 43 patients treated with selective β-blockers, group 2: 8 patients with carvedilol) and retrospectively analyzed the efficacy of the respective β-blocker therapy in suppressing cardiac events. Cardiac events were observed in 11 patients of group 1 (26%) but none in group 2 during a follow-up period of 83 ± 80 months (P = 0.098). Conclusions: Carvedilol may be a potentially beneficial therapy for genotyped LQT2 patients who are refractory to other β selective blockers.