PO-01-240 UTILITY OF FUNCTIONAL CHARACTERIZATION IN THE PROMOTION OR DEMOTION OF CLINICALLY ENCOUNTERED VARIANTS OF UNCERTAIN SIGNIFICANCE IN THE THREE MOST COMMON LONG QT SYNDROME-CAUSATIVE GENES: , KCNH, AND

Genetic testing for cardiac channelopathies such as long QT syndrome (LQTS) and Brugada (BrS) is standard of care. Although the American College Medical Genetics (ACMG) guidelines variant interpretation have provided a framework distinguishing pathogenic variants from benign, many rare genetic remain classified uncertain significance (VUS) due to lack epidemiologic or functional data either promote demote benign status, respectively. To functionally characterize clinically encountered VUSs in three most common LQTS-causative genes: KCNQ1 (LQT1), KCNH2 (LQT2), SCN5A (LQT3 BrS1) vitro by patch clamp technique provide additional evidence promotion/demotion. A total 89 nonsynonymous VUS (15 KCNQ1, 19 KCNH2, 55 SCN5A) were engineered site directed mutagenesis expressed HEK293 cells TSA201 cells. Whole cell patch-clamp was used these determine gain-of-function (GOF), loss-of-function (LOF), normal channel function. Overall, majority (50/89; 56.2%) studied displayed wild-type-like electrophysiological phenotype enabled demotion likely status. The remaining (39/89; 43.8%) promoted status based on GOF LOF signature following analysis. Among 15 variants, 11 (73.3%) had function, 3 (20.0%) LOF, 1 (6.7%) GOF. Of (57.9%) 5 (26.3%) (15.8%) Finally, among 28 (50.9%) exhibited (34.5%) 8 (14.5%) Here, we characterization identified during course indicated testing. Consistent with clinical index suspicion VUS-positive subject, 44% while 56% demoted variant. Whether test companies will incorporate this characterized compendium issue amended reports awaits their review incorporation into internal annotation.