Cardiogenetics

Introduction: Clinical variability within families harbouring disease-causing genetic variants hampers clinical care and risk stratification. We studied a multigenerational family presenting with sinus bradycardia and long QT syndrome type 2 (LQTS2). The family harboured a pathogenic variant in KCNH2, which co-segregated with the observed LQTS2. We studied the genetic cause of the high occurrence of sinus bradycardia in this family. Methods: Clinical data was collected, including heart rate, QT-interval, symptoms, and echocardiographic parameters. QTc was calculated using the Bazett and the Fridericia formula. Sanger sequencing of HCN4 was performed, followed by segregation analysis of the identified variant with sinus bradycardia. The biophysiological consequences of two variants, KCNH2-p.L69P (c.206T>C) and HCN4-p.R666W (c.1996C>T), were assessed by patch-clamp experiments. Therefore, a heterologous model was generated by transfection of HEK293A or CHO-k1 cells, respectively. Results: Sanger sequencing of HCN4 identified HCN4-p.R666W (c.1996C>T), which has a stronger segregation with the observed sinus bradycardia than KCNH2-p.L69P. Patch-clamp experiments revealed that KCNH2-p.L69P and HCN4-p.R666W lead to a decrease in the corresponding current densities, which explains the LQTS and sinus bradycardia observed in the patients. Carriers of both genetic variants have a more severe LQTS2 phenotype, reflected in longer QT and higher incidence of syncope. Conclusions: We identified two (likely) pathogenic variants, KCNH2-p.L69P and HCN4-p.R666W, co-segregating with LQTS2 and sinus bradycardia, respectively. Patients carrying both variants showed a more severe phenotype. These findings highlight the importance of additional genetic testing when discordant features are present, thereby enabling more accurate diagnosis, risk prediction, and management.

Background: PRKAG2-related disease is an autosomal dominant disorder caused by pathogenic variants in the PRKAG2 gene, leading to glycogen accumulation in cardiomyocytes. It is characterized by left ventricular hypertrophy (LVH), ventricular pre-excitation, and conduction disease. Due to the rarity of the condition and the frequent occurrence of private variants, functional or pathological testing is required for definitive pathogenicity classification. Case Presentation: We describe a 22-year-old male referred for evaluation after experiencing exertional dyspnea and a syncopal episode. Family history revealed sudden cardiac deaths and conduction disease requiring pacemaker implantation. The patient exhibited mild LVH on imaging, conduction abnormalities on electrophysiological study, and a heterozygous PRKAG2 variant (c.1643C>T; p.Ser548Leu), classified as likely pathogenic according to ACMG guidelines. Cascade screening identified the variant in three family members, one of whom exhibited a positive phenotype. Endomyocardial biopsy revealed glycogen accumulation, providing histopathological confirmation of PRKAG2-related disease. Conclusions: This case underscores the importance of integrating genetic, clinical, and histopathological data in variant interpretation. Endomyocardial biopsy can provide definitive evidence to reclassify a PRKAG2 variant as pathogenic, thereby guiding management and family screening.

Background: Regular endurance training induces physiological changes in cardiac structure and function. The precise epigenetic mechanisms by which cardiovascular adaptations are mediated are still unclear. This review seeks to clarify the role of epigenetic regulation in exercise-induced cardiovascular adaptation. Methods: This systematic review was conducted in accordance with the PRISMA guidelines up to 30 April 2025, using the databases PubMed, VHL, and LILACS Plus. Studies were included if they focused on microRNA expression and DNA methylation in individuals with cardiovascular disease who underwent endurance training. Results: Six articles, including 384 participants with heart failure, coronary artery disease, and hypertension, were included in the final analysis. Changes in DNA methylation and microRNA expression of specific genes involved in cardiovascular structural and functional adaptation were observed. Significant improvements were found in body composition, VO_2peak, systolic and diastolic blood pressure, and left ventricular function and structure. Conclusions: Endurance training has a positive impact on epigenetic mechanisms related to cardiovascular structural and functional adaptation. A clear causal link between epigenetic modifications and clinical outcomes remains to be established.