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Background: Ethnic diversity of the population in the region of Siberia suggests the existence of different germline mutations in the BRCA1/2 genes associated with breast and ovarian cancer in different ethnic populations, but spectrum of these mutations has not been studied. Objective: Our aim was to evaluate the frequency of the most common mutations BRCA1 / 2 (BRCA1 5382insC, BRCA1 185delAG, BRCA1 4153delAG, BRCA1 T300G, BRCA2 6174delT) in women diagnosed with breast cancer among indigenous people and newcomers living in Siberia. Methods: We tested 1281 genomic DNA samples for the presence of BRCA1 5382insC mutation in patients diagnosed with breast cancer considering no family history. 72 patients having hereditary cancer signs were tested for the mutations BRCA1 185delAG, BRCA1 4153delAG, BRCA1 T300G, BRCA2 6174delT. Results: Out of 765 patients of Slavic ethnic group, 27 women (3.5%) were carriers of allele BRCA1 5382insC. The frequencies of mutations in patients with signs of hereditary cancer were: 8.3% in group of young patients (under 40 years), 20.0% in patients with bilateral cancer and 5.7% in patients with family history of breast or ovarian cancers. We tested 516 BC patients residing on the territory of the Buryat-Aginsky district, Republics of Tyva and Altai. Out of them, there were 197 patients among the indigenous population (buryats, tuvinians, altaians), and 319 patients among newcomers (Slavic ethnics). Mutations BRCA1 5382insC were detected only in women from Slavic ethnic groups. The frequency of BRCA1 5382insC mutation was 6% in the group where family history was excluded and 14% in the group of patients with characteristics of family cancer. Allele BRCA1 5382insC was not found in indigenous breast cancer patients, although 59 patients had signs of hereditary cancer. In women from Slavic ethnic group, the BRCA1 185delAG, BRCA1 4153delAG and BRCA1 T300G mutations were detected in 9.1% of cases and were not found in patients among the indigenous population. Conclusion: studies of mutations in the BRCA1 gene in breast cancer patients from Siberia confirmed data on the high frequency of «founder mutation» BRCA1 5382insC in Slavic population and indicate the advisability of further studies to identify the genes responsible for the occurrence of hereditary breast cancer in the indigenous population.

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We described six new sequence variants that have never been published in the literature or databases. Further studies are required to confirm the impact of new sequence variants on the risk of breast cancer in the Buryat Mongol population.