If there is a history of BC and OC in the family, as a rule, its members are carriers of one of the following allelic variants: BRCA1 5382insC, BRCA1 4153delA, BRCA1 185delAG, BRCA1 T300G, BRCA1 2080delA, BRCA2 6174delT, CHEK2 1100delC, CHEK2 I157T, and BLM C1642T in Eastern Europe and in Russia [11,12,13,14,15]. The gene discussed is BLM; the disease is breast cancer.