Multiplexed Assays of Variant Effect and Reclassification of TYR Variants in Chinese Patients with Oculocutaneous Albinism

Oculocutaneous albinism type 1, caused by mutations in the tyrosinase gene TYR gene, is the most common form of albinism worldwide. Owing to the variants of uncertain significance (VUSs) classified by the American College of Medical Genetics and Genomics guidelines, patients who carry these VUSs do not receive a definitive molecular diagnosis. To clarify the pathogenicity of the VUS variants, we conducted multiplexed assays of variant effect to reclassify the TYR VUS variants. Protein expression, melanin production, enzyme activity, and subcellular localization were applied to 46 selected variants: 27 VUSs from 1243 patients with albinism, 14 pathogenic/likely pathogenic, and 5 benign/likely benign control variants. Odds of pathogenicity values were calculated as recommended by Brnich et al (2019). By conducting multiplexed assays of variant effect, PS3_moderate or PS3_supporting evidence was applied. By following the American College of Medical Genetics and Genomics guidelines, 25 of 27 VUSs were reclassified as likely pathogenic, and 3 of 11 likely pathogenic variants were reclassified as pathogenic. Therefore, 19 of 20 (95%) previously undiagnosed patients had a molecular diagnosis of oculocutaneous albinism type 1. In addition, the pathogenic mechanisms of TYR have been elucidated and categorized. These comprehensive multiplexed assays of variant effect provide a robust approach for curating TYR VUS. This study advocates multiplexed assays of variant effect for validating an accurate genotype-phenotype relationship.