Loss of sodium current caused by a Brugada syndrome-associated variant is determined by patient-specific genetic background.

Background: Brugada syndrome (BrS) is an inherited cardiac arrhythmogenic disease that predisposes patients to sudden cardiac death. It is associated with mutations in SCN5A, which encodes the cardiac sodium channel alpha subunit (Na _V 1.5). BrS-related mutations have incomplete penetrance and variable expressivity within families.
Objective: The purpose of this study was to determine the role of patient-specific genetic background on the cellular and clinical phenotype among carriers of Na _V 1.5_p.V1525M.
Methods: We studied sodium currents from patient-specific human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and heterologously transfected human embryonic kidney (HEK) tsA201 cells using the whole-cell patch-clamp technique. We determined gene and protein expression by quantitative polymerase chain reaction, RNA sequencing, and western blot and performed a genetic panel for arrhythmogenic diseases.
Results: Our results showed a large reduction in I _Na density in hiPSC-CM derived from 2 V1525M single nucleotide variant (SNV) carriers compared with hiPSC-CM derived from a noncarrier, suggesting a dominant-negative effect of the Na _V 1.5_p.V1525M channel. I _Na was not affected in hiPSC-CMs derived from a V1525M SNV carrier who also carries the Na _V 1.5_p.H558R polymorphism. Heterozygous expression of V1525M in HEK-293T cells produced a loss of I _Na function, not observed when this variant was expressed together with H558R. In addition, the antiarrhythmic drug mexiletine rescued I _Na function in hiPSC-CM. SCN5A expression was increased in the V1525M carrier who also expresses Na _V 1.5_p.H558R.
Conclusion: Our results in patient-specific hiPSC-CM point to a dominant-negative effect of Na _V 1.5_p.V1525M, which can be reverted by the presence of Na _V 1.5_p.H558R. Overall, our data points to a role of patient-specific genetic background as a determinant for incomplete penetrance in BrS.
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