Telethonin variants found in Brugada syndrome, J-wave pattern ECG, and ARVC reduce peak Na 1.5 currents in HEK-293 cells.

Background: Telethonin (TCAP) is a Z-disk protein that maintains cytoskeletal integrity and various signaling pathways in cardiomyocytes. TCAP is shown to modulate α-subunit of the human cardiac sodium channel (hNa 1.5) by direct interactions. Several TCAP variants are found in cardiomyopathies. We sought to investigate whether TCAP variants are associated with arrhythmia syndromes.

Methods: Mutational analyses for TCAP were performed in 303 Japanese patients with Brugada syndrome, arrhythmogenic right ventricular cardiomyopathy, and J-wave pattern ECG. Using patch-clamp techniques, electrophysiological characteristics of hNa 1.5 were studied in HEK-293 cells stably expressing hNa 1.5 and transiently transfected with wild-type (WT) or variant TCAP.

Results: We identified two TCAP variants, c.145G>A:p.E49K and c.458G>A:p.R153H, in four individuals. p.E49K was found in two patients with ARVC or BrS. p.R153H was found in two patients with BrS or J-wave pattern ECG. No patient had variant hNa 1.5. Patch-clamp experiments demonstrated that peak sodium currents were significantly reduced in cells expressing p.R153H and p.E49K compared with WT-TCAP (66%, p.R153H; 72%, p.E49K). Voltage dependency of peak IV curve was rightward-shifted by 5 mV in cells expressing p.E49K compared with WT-TCAP. Voltage dependency of activation was not leftward-shifted by p.R153H, while voltage dependency of steady-state inactivation was leftward-shifted by p.E49K.

Conclusions: We found two TCAP variants in the patients with BrS, J-wave pattern ECG, and ARVC that can cause loss-of-function of the hNa 1.5 in heterologous expression systems. Our observation suggests that these variants might impair I and be associated with the patients' electrophysiological phenotypes. Further studies linking our experimental data to clinical phenotypes are warranted.