Breast cancer is the most common cancer among women in Russia. In 2014 61 308 breast cancer cases were diagnosed in Russia, including 1577 cases in the Republic of Tatarstan region. Among them nearly 10% has familiar history breast or ovarian cancer. The number of founder BRCA1 and 2 mutations are known to be responsible for hereditary breast cancer. It is also known that the frequency of occurrence of certain founder mutations varies in different countries and nationalities. It was previously reported that frequent for Slavic population BRCA mutation is not found in Tatar women with hereditary breast cancer. We screened BRCA genes of 24 Tatar women with breast cancer for presence alternative founder mutations.
The DNA was isolated from patients' blood using NucleoSpin Tissue kit (Macherey Nagel) in accordance with manufacturer instructions. 400 nanogram of DNA was sheared by sonication using a Q800R2 instrument (Q-Sonica). Further steps of library preparation were performed using a KAPA Library preparation kit (Kapabiosystems) followed by targeted gene enrichment by NimbleGen SeqCap EZ Choice (Roche) according to the manufacturer's instructions. The library was sequenced using an Illumina MiSeq instrument with read length 249 bp from each end of the fragment.
Three previously reported BRCA1 pathogenic mutations, c.5161C > T, c. 5382insC and 300T > G and one BRCA2 pathogenic mutation c.468dup were observed in 4 patients (16,7%). Additionally, novel variant BRCA2 c7544C > T was predicted to be pathogenic in silico. Only two of the observed mutations is included in routine BRCA testing in Russia (185delAG, 4153delA, 5382insC, 3819delGTAAA, 3875delGTCT, 300T > G, (Cys61Gly), 2080delA, 6174delT) and usage of standard real-time PCR kits would cause false negative results.
The study demonstrated that breast cancer individuals in Tatar ethnos possess different founder mutations from Slavic Russian population in BRCA genes. Thus, current genetic testing protocol for Russian BRCA1 founder mutation is not enough sensitive for clinical use and nationality has to be taken into account.
Clinical trial identification
Legal entity responsible for the study
Kazan (Volga Region) Federal university Kazan Clinical Oncology Center Federal Research and Clinical Center, FMBA
All authors have declared no conflicts of interest.