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In Russia, more than 50,000 women are diagnosed with breast cancer (BC) every year. Russia is a multinational country — about 200 ethnic groups live on its territory. Khakass, Buryats, Tuvans and other ethnic groups show higher rate of increase in BC incidence and a younger age of first diagnosed BC compared to Caucasian ethnicities. We focused on Tuvan ethnic group to find specific genetic aberrations associated with BC. There are no BC prevention models as well as standards for the treatment of inherited BC in Tuvans. In this context, the search for genetic markers of early cancer detection and the development of criteria for therapy response are relevant. Aim: To identify hereditary mutations in BC-associated genes in Tuvan women. Materials and Methods: 24 patients with early-onset BC (range, 25 to 46 years) were enrolled in the study. Genomic DNA isolated from blood samples was used to prepare libraries using a capture-based target enrichment kit covering 27 genes (ATM, APC, BARD1, BRCA1, BRCA2, BRIP1, CDH1, CHEK2, EPCAM, FAM175A, MLH1, MRE11A, MSH2, MSH6, MUTYH, NBN, PALB2, PIK3CA, PMS2, PMS2CL, PTEN, RAD50, RAD51C, RAD51D, STK11, TP53 and XRCC2). Next-generation sequencing was performed using the Illumina NextSeq500 System. Results: In our study, one pathogenic mutation was detected in BRCA1 (rs80357868) gene (prevalence of 4%, 1/24). We identified the truncating 3875_3878delGTCT mutation of BRCA1 gene in Tuvans BC patient aged 34 years. We also detected three mutations that were probably damaging by PolyPhen2 and/or deleterious by SIFT in ATM (rs781023264), MUTYH (rs199840380) and RAD51D (rs145309168) genes. Conclusion: To the best of our knowledge, this is the first report that describes the highly pathogenic variant in the BRCA1 gene (rs80357868) and possibly damaging (PolyPhen2) germline variants in the ATM (rs781023264), MUTYH (rs199840380) and RAD51D