Explore the vast range of titles available.

Human variants in plakophilin-2 (PKP2) associate with most cases of familial arrhythmogenic cardiomyopathy (ACM). Recent studies show that PKP2 not only maintains intercellular coupling, but also regulates transcription of genes involved in Ca2+ cycling and cardiac rhythm. ACM penetrance is low and it remains uncertain, which genetic and environmental modifiers are crucial for developing the cardiomyopathy. In this study, heterozygous PKP2 knock-out mice (PKP2-Hz) were used to investigate the influence of exercise, pressure overload, and inflammation on a PKP2-related disease progression. In PKP2-Hz mice, protein levels of Ca2+-handling proteins were reduced compared to wildtype (WT). PKP2-Hz hearts exposed to voluntary exercise training showed right ventricular lateral connexin43 expression, right ventricular conduction slowing, and a higher susceptibility towards arrhythmias. Pressure overload increased levels of fibrosis in PKP2-Hz hearts, without affecting the susceptibility towards arrhythmias. Experimental autoimmune myocarditis caused more severe subepicardial fibrosis, cell death, and inflammatory infiltrates in PKP2-Hz hearts than in WT. To conclude, PKP2 haploinsufficiency in the murine heart modulates the cardiac response to environmental modifiers via different mechanisms. Exercise upon PKP2 deficiency induces a pro-arrhythmic cardiac remodeling, likely based on impaired Ca2+ cycling and electrical conduction, versus structural remodeling. Pathophysiological stimuli mainly exaggerate the fibrotic and inflammatory response.

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.