Brugada syndrome (BrS) is an autosomal dominant cardiac disorder. It is commonly associated with loss of function mutations in the SCN5A gene, encoding the cardiac voltage gated sodium channel. BrS-associated SCN5A variants can therefore lead to reduced cardiac excitability and conduction velocity, often resulting in patients experiencing abnormal cardiac rhythms, ventricular arrhythmias and sudden cardiac death.

When a patient presents with a BrS-associated mutation through genetic testing, it is often difficult to assess if the mutation is benign or pathogenic. This is because 79% of known BrS-associated mutations are currently labelled as a variant of uncertain significance (VUS). Discovery of variant pathogenicity is hampered by low throughput functional measurements and differential measurement conditions between laboratories.

Advances in high throughput functional techniques, such as automated patch-clamp (APC) assays, can accelerate the interpretation and reclassification of VUS. A recent study aimed to establish and calibrate an APC assay on the high-throughput SyncroPatch 384 system to classify four different VUS found in four families with suspected BrS.

The study first established an in vitro SCN5A-BrS APC assay across two independent institutes; the Vanderbilt University Medical Center and the Victor Chang Cardiac Research Institute. The assay was calibrated using variants of known pathogenicity stably expressed in HEK293 cells. The functional readouts generated by the two research sites showed strong correlation together and accurately distinguished between known benign and pathogenic variants.

SCN5A VUS from four patients were subsequently analyzed with the APC assay which revealed a loss of function in all variants. After providing the functional data to the relevant clinical sites, interpretation of the American College of Medical Genomics guidelines allowed for reclassification of three out of four variants from VUS to likely pathogenic.

In summary, this study provides a robust validated technique to determine SCN5A variant pathogenicity. It highlights the importance of multicenter cooperation to generate accurate functional assays, while emphasizing the continuing need for high throughput measurements to aid in personalized treatment strategies.

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Find the full article here: https://www.ahajournals.org/doi/10.1161/CIRCGEN.124.004569

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