Deleterious mutations in the RAD51C gene, which encodes a DNA double-strand break (DSB) repair protein, have been reported to confer high-penetrance susceptibility to both breast and ovarian cancer. To confirm this we conducted a mutation screen of the RAD51C gene in 192 probands from high-risk breast and/or ovarian cancer families that do not carry BRCA1 or BRCA2 mutations. The nine exons of the RAD51C gene containing protein coding sequence were screened for mutations in genomic DNA from family probands by high-resolution melting (HRM) analysis and direct DNA sequencing. Four missense variants, p.Ser364Gly, p.Ala126Thr, p.Val169Ala, and p.Thr287Ala were detected in six patients. The p.Ser364Gly variant is a novel variant predicted to have little influence on RAD51C activity. The p.Ala126Thr and p.Val169Ala variants have been reported to have no association with risk of breast cancer in a case-control study. However, p.Thr287Ala disrupts the DNA repair activity of RAD51C, suggesting some influence on risk. Consistent with published results from similar follow-up studies, we suggest that RAD51C mutations are rare events among high-risk breast cancer and breast/ovarian cancer families. Large population-based studies will be needed to reliably assess the prevalence and penetrance of inactivating mutations in the RAD51C susceptibility gene.
BRCA1 and BRCA2 are the most well-known breast cancer susceptibility genes. Additional genes involved in DNA repair have been identified as predisposing to breast cancer. One such gene, RAD51C, is essential for homologous recombination repair. Several likely pathogenic RAD51C mutations have been identified in BRCA1- and BRCA2-negative breast and ovarian cancer families. We performed complete sequencing of RAD51C in germline DNA of 286 female breast and/or ovarian cancer cases with a family history of breast and ovarian cancers, who had previously tested negative for mutations in BRCA1 and BRCA2. We screened 133 breast cancer cases, 119 ovarian cancer cases, and 34 with both breast and ovarian cancers. Fifteen DNA sequence variants were identified; including four intronic, one 5′ UTR, one promoter, three synonymous, and six non-synonymous variants. None were truncating. The in-silico SIFT and Polyphen programs were used to predict possible pathogenicity of the six non-synonomous variants based on sequence conservation. G153D and T287A were predicted to be likely pathogenic. Two additional variants, A126T and R214C alter amino acids in important domains of the protein such that they could be pathogenic. Two-hybrid screening and immunoblot analyses were performed to assess the functionality of these four non-synonomous variants in yeast. The RAD51C-G153D protein displayed no detectable interaction with either XRCC3 or RAD51B, and RAD51C-R214C displayed significantly decreased interaction with both XRCC3 and RAD51B (p<0.001). Immunoblots of RAD51C-Gal4 activation domain fusion peptides showed protein levels of RAD51C-G153D and RAD51C-R214C that were 50% and 60% of the wild-type, respectively. Based on these data, the RAD51C-G153D variant is likely to be pathogenic, while the RAD51C- R214C variant is hypomorphic of uncertain pathogenicity. These results provide further support that RAD51C is a rare breast and ovarian cancer susceptibility gene.
An inherited predisposition to breast cancer underlies 5-10% of breast tumors. High-risk BRCA1 and BRCA2 genes result in an 85% lifetime risk of breast cancer and a 20-60% lifetime risk of ovarian cancer. Next-generation sequencing or massive parallel sequencing are now established testing methods that enable screening for many genes that predispose to heterogeneous hereditary cancer syndromes (22 genes are required by the health insurance companies). In addition to BRCA1 and BRCA2, inherited mutations in other genes predispose to breast and/or ovarian cancer. High-risk breast cancer genes include TP53, STK11, CDH1, PTEN, PALB2, and NF1, while moderate-risk (2-4 times increased risk) breast cancer genes include ATM, CHEK2, and NBN. Moderate risk is also suggested for Lynch syndrome, MUTYH, BRIP1, RAD51C, RAD51D, BARD1, FANCA, FANCC, FANCM, BLM, WRN genes. In heterozygotes for other recessive syndromes the risk of developing breast cancer is subject to current research. Low-risk genes are (mostly) irrelevant from a clinical perspective. Other genes that increase the risk of ovarian cancer include the genes for Lynch syndrome, the BRIP1, RAD51C and RAD51D genes. Preventive care should be proposed based on assumed cumulative breast cancer risk (see http: //www.mamo.cz): a risk of >20% for BRCA1/2, TP53, PTEN, STK11, CDH1, PALB2, CHEK2, ATM, and NF1; and a risk of 10-20% for BRIP1, RAD51C, RAD51B, BARD1, FANCA, FANCC, FANCM, NBN, BLM, and WRN. The genetic risk should be assessed by a geneticist and be based on inherited mutations and empirical risk according to family history. Prophylactic mastectomy is considered for high-risk gene carriers but not for moderate-risk gene carriers; however, it may be considered if there is an underlying family history, a risk of parenchyma of the mammary gland, or other risk factors. Ovarian cancer risk increases significantly in carriers of the BRIP1, RAD51C, and RAD51D genes. For prevention of ovarian cancer, prophylactic salpingo-oophorectomy is an important component of preventive care. In ovarian cancer families with no identified risk germline mutation, preventive salpingo-oophorectomy is not routinely recommended but may be considered as the only efficient method of prevention due to the increased empirical risk (4 times) of ovarian cancer in first-degree relatives. Supported by the grant project MH CZ - RVO (MMCI, 00209805), AZV 15-27695A and AZV 16-29959A. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Submitted: 17. 5. 2019 Accepted: 31. 5. 2019.
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