Identification of p.C335R Variant in a Large Family with Dilated Cardiomyopathy and Conduction Disease.

Introduction: Familial dilated cardiomyopathy (DCM) is clinically variable and has been associated with mutations in more than 50 genes. Rapid improvements in DNA sequencing have led to the identification of diverse rare variants with unknown significance (VUS), which underlines the importance of functional analyses. In this study, by investigating human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), we evaluated the pathogenicity of the p.C335R sodium voltage-gated channel alpha subunit 5 () variant in a large family with familial DCM and conduction disease.

Methods: A four-generation family with autosomal dominant familial DCM was investigated. Next-generation sequencing (NGS) was performed in all 16 family members. Clinical deep phenotyping, including endomyocardial biopsy, was performed. Skin biopsies from two patients and one healthy family member were used to generate human-induced pluripotent stem cells (iPSCs), which were then differentiated into cardiomyocytes. Patch-clamp analysis with oocytes and iPSC-CMs were performed.

Results: A variant (c.1003T>C; p.C335R) could be detected in all family members with DCM or conduction disease. A novel truncating variant (p.Ser24998LysfsTer28) could also be identified in two family members with DCM. Family members with the variant (p.C335R) showed significantly longer PQ and QRS intervals and lower left ventricular ejection fractions (LV-EF). All four patients who received CRT-D were non-responders. Electrophysiological analysis with oocytes showed a loss of function in p.C335R. Na channel currents were also reduced in iPSC-CMs from DCM patients. Furthermore, iPSC-CM with compound heterozygosity ( p.C335R and ) showed significant dysregulation of sarcomere structures, which may be contributed to the severity of the disease and earlier onset of DCM.

Conclusion: The p.C335R variant is causing a loss of function of peak INa in patients with DCM and cardiac conduction disease. The co-existence of genetic variants in channels and structural genes (e.g., p.C335R and ) increases the severity of the DCM phenotype.