Germline mutation in the RAD51B gene confers predisposition to breast cancer

Abstract

Background: Most currently known breast cancer predisposition genes play a role in DNA repair by homologous recombination. Recent studies conducted on RAD51 paralogs, involved in the same DNA repair pathway, have identified rare germline mutations conferring breast and/or ovarian cancer predisposition in the RAD51C, RAD51D and XRCC2 genes. The present study analysed the five RAD51 paralogs (RAD51B, RAD51C, RAD51D, XRCC2, XRCC3) to estimate their contribution to breast and ovarian cancer predisposition.

Methods: The study was conducted on 142 unrelated patients with breast and/or ovarian cancer either with early onset or with a breast/ovarian cancer family history. Patients were referred to a French family cancer clinic and had been previously tested negative for a BRCA1/2 mutation. Coding sequences of the five genes were analysed by EMMA (Enhanced Mismatch Mutation Analysis). Detected variants were characterized by Sanger sequencing analysis.

Results: Three splicing mutations and two likely deleterious missense variants were identified: RAD51B c.452 + 3A > G, RAD51C c.706-2A > G, RAD51C c.1026 + 5_1026 + 7del, RAD51B c.475C > T/p.Arg159Cys and XRCC3 c.448C > T/p.Arg150Cys. No RAD51D and XRCC2 gene mutations were detected. These mutations and variants were detected in families with both breast and ovarian cancers, except for the RAD51B c.475C > T/p.Arg159Cys variant that occurred in a family with 3 breast cancer cases.

Conclusions: This study identified the first RAD51B mutation in a breast and ovarian cancer family and is the first report of XRCC3 mutation analysis in breast and ovarian cancer. It confirms that RAD51 paralog mutations confer breast and ovarian cancer predisposition and are rare events. In view of the low frequency of RAD51 paralog mutations, international collaboration of family cancer clinics will be required to more accurately estimate their penetrance and establish clinical guidelines in carrier individuals.

Figure 1

mRNA analysis for RAD51C splicing mutations showing exon skipping. (A) Electropherograms of Sanger sequencing analysis for a control sample with wild type RAD51C mRNA only (left) and for RAD51C c.706-2A > G mutation with two types of mRNA: wild type mRNA and mRNA with exon 5 skipping (right). (B) Electropherograms of Sanger sequencing analysis for a control sample with wild type RAD51C mRNA only (left) and for RAD51C c.1026 + 5_1026 + 7del mutation with two types of mRNA: wild type mRNA and mRNA with exon 8 skipping (right).

Figure 2

RAD51B immunohistochemistry in breast tissue of patient carrying the RAD51B c.452 + 3A > G mutation. A brown staining of moderate intensity is observed in the nucleus of non tumor epithelial cells located in normal duct (ND) of the breast tissue. In comparison, no significant staining is detected in the nucleus of invasive carcinoma cells (ICC).

Figure 3

Pedigrees for RAD51 paralog mutation and likely causal variant carriers. Individuals with breast cancer (BC) are shown as red circles, ovarian cancer (OC) as purple circles, and other cancers as blue circles. SC: stomach cancer; UC: uterine cancer; PC: pancreas cancer. Disease and age in years at diagnosis are given underneath the symbol. The index case is indicated with an arrow. No co-segregation studies have yet been performed, except for RAD51C c.706-2A > G: tested relative with OC carried the mutation, indicated by (+).