Pathogenicity Reclassification of Genetic Variants Related to Early-Onset Breast Cancer among Buryat Women

Background: Germline alterations in ATM, BRCA1, BRCA2, and other genes are responsible for early-onset breast cancer. However, up to 20% of molecular tests report genetic variant of unknown significance (VUS) or novel variants that have never been previously described and their clinical significance are unknown. An existing open access databases (ClinVar, BIC, and ENIGMA and other) play an important role in the interpretation of VUS, but in Asian populations the interpretation of VUS is still difficult due to restricted data. This study aimed to reclassify the genetic variants by using the ActiveDriveDB database that annotates variants through the lens of sites of post-translational modifications. Methods: Our study included young Buryat BC patients, anthropologically belonging to the Central Asia. Genomic DNA was used to prepare libraries. NGS sequencing was performed on a NextSeq 500 System. Results: We re-examined 135 rare variants (41 VUS, 25 conflicting, 64 benign and 5 new variants). We identified 10 out of 135 (7.4%) mutations that affected the sites of post-translational modification in proteins. Of 135 rare mutations, 1 benign variant was reclassified as network-rewiring - motif loss mutation, 3 VUS and 1 new variant were reclassified as distal PTM- mutations, 2 new and 1 benign variant were classified as proximal PTM- mutations and 1 benign and 1 conflicting variant were classified as direct PTM- mutations. Conclusions: For the first time, 7.4% (10 out of 135) of mutations that affected the sites of post-translational modification in proteins were identified among Buryat women with early-onset breast cancer.