High rate of mutations in the BRCA1, BRCA2, CHEK2, NBN, and BLM genes in Russian ovarian cancer patients

Abstract

Background. The early diagnosis of ovarian cancer (OC) is an important problem in modern gynecological oncology due to significant detection rates for late-stage tumors. Intensive screening of patients from high-risk groups that include OC predisposition gene mutation carriers is indicated. Subjects and methods. An unselected group of 202 patients with OC and two control groups of blood donors: 591 healthy females; 1197 persons (including 591 females, 606 males) were examined. Patients and healthy individuals who identified themselves as ethnic Russians and residents of the Russian Federation participated in the study. Whole peripheral blood samples were collected at the Clinical Subdivisions of the N.N. Blokhin Russian Cancer Research Center and at the Department of Transfusiology of the Acad. B.V. Petrovsky Russian Research Center of Surgery in 2012–2013. Informed consent was obtained from all the participants. DNA was extracted using a Prep-GS-Genetics reagent kit. Real-time polymerase chain reaction genotyping assay was carried out by melting-curve analysis employing an BRCA SNP genotyping kit (BRCA1 and BRCA2 gene mutations) and original oligonucleotides (CHEK2, NBN, and BLM gene mutations). Thirteen population-specific mutations, including 7 (185delAG, 4153delA, 5382insC, 3819delGTAAA, 3875delGTCT, 300T>G, and 2080delA) in the BRCA1 gene, 1 (6174delT) in the BRCA2 gene, 3 (1100delC, IVS2+1G>A, and 470T>C) in the CHEK2 gene, 1 (657delACAAA) in the NBN gene, and 1 (1642C>T) in the BLM gene, were genotyped. Polymerase chain reaction was performed using a DTprime real-time detection thermal cycler. Results and discussion. BRCA1 and BRCA2 gene mutations were detected in 46 (22.8 %) patients with OC; the prevailing mutation in the BRCA1 gene was 5382insC (58.7 %). OC was diagnosed in 32.6 % of the patients aged 51 years or older. The rate of moderate-penetrance mutations (1100delC and IVS2+1G>A in the CHEK2 gene, 657del5 in the NBN gene, and 1642C>T in the BLM gene) was 0.5–1.0 % in the group of OC patients and 0–0.3 % in the control group of healthy women. The majority of these patients (5/6) were diagnosed with OC at age less than 50 years. The CHEK2 mutation, 470T>C, was more frequently encountered in the control group (6.6 %) than in the OC patient group (5.0 %). High rate of the CHEK2 mutation, IVS2+1G>A, was first shown for OC patients in the Russian Federation, the odds ratio was 11.9 (95 % confidence interval, 9.5–14.3; p = 0.056). It was preliminarily concluded that it played an important role in the development of OC in the Russian population; our findings should be verified in further investigations. The difference in the rate of mutations, such as 1100delC, IVS2+1G>A and 470T>C in the CHEK2 gene, 657del5 in the NBN gene, 1642C>T in the BLM gene, were insignificant in the patient and control groups, which may be related to the low population rate of these genetic markers and, in case of the CHEK2 mutation, 470T>C, may be linked to its low penetrance. By taking into account the fact that numerous studies have proven the clinical significance of all examined moderate-penetrance mutations whose prevalence in the Russian population has been confirmed by the authors of this paper, the inclusion of the mutations in a diagnostic panel to detect hereditary predisposition to OC is substantiated. The associated risks are higher for the rare mutations leading to the formation of truncated nonfunctional proteins, which are 1100delC and IVS2+1G>A in the CHEK2 gene, 657del5 in the NBN gene, and 1642C>T in the BLM gene. The penetrance of the CHEK2 mutation, 470T>C, is lower, which should be kept in mind during medical genetic counselling. Conclusion. The total rate of mutations in the BRCA1, BRCA2, CHEK2, NBN, and BLM genes in patients with OC was 30.7 %, which determines the expediency of molecular genetic screening in this category of patients.