Abstract A025: Screening for genomic rearrangements and germline mutations in BRCA1 and BRCA2 genes in hereditary breast cancer unrelated Brazilian families

Abstract

Abstract Breast cancer (BC) is one of the most important causes of mortality within women worldwide. About 90% of breast cancer cases are sporadic and 5 to 10% are due to hereditary predisposition. Hereditary Breast Cancer (HBC) is an autosomal dominant disease, characterized by germline mutations in BRCA1 and BRCA2 genes that confers high risk of developing breast and ovarian cancers. Large genomic rearrangements (LGRs), including deletions and duplications, are responsible for up to 27% in BRCA1 gene and are less common in the BRCA2 gene, depending on the population. The aim of the present study was to evaluate BRCA1 and BRCA2 germline mutations and the prevalence of LGRs in Brazilian families that fulfilled clinical criteria for HBC. In total, 128 unrelated families were evaluated, from which 108 fulfilled clinical criteria for hereditary breast and ovary cancer (HBOC), 20 for hereditary breast and colon cancer (HBCC) and 32 met both clinical criteria. DNA samples from peripheral blood were used to evaluate by direct sequencing the complete coding sequences and exon-intron boundaries of BRCA1 and BRCA2, and also the CHEK2 1100delC variant. To determine pathogenicity of variants of uncertain significance (VUS), Breast Cancer Information Core, IARC-LOVD database and web-based protein prediction algorithms such as SIFT, PolyPhen and align-GVGD were used. The non-carriers of BRCA1/2 mutations were selected for MLPA (multiplex ligation-dependent probe amplification) analysis for the evaluation of large genomics rearrangements. The prevalence of pathogenic mutations in this study was: 22.5% including 21 in BRCA1 (2 splice site, 2 missense, 9 frame shift, 6 nonsense and 2 LGR) and 7 in BRCA2 (3 frameshift and 4 nonsense) and one proband harbored CHEK2 1100delC variant. Seven (25%) pathogenic mutations were firstly described, including a novel splice-site BRCA1 mutation, whose pathogenicity was confirmed by transcriptional analysis. Among the VUS carriers, 19 variants were distinct and two of them were described for the first time. The VUS evaluation by three protein prediction algorithms (Polyphen, SIFT and GVGD-Align) showed that seven were classified as likely pathogenic by at least one of them (four in one algorithm, two in two algorithms and one in all three algorithms). In our series, we have detected 2 LGR (1,56%) in BRCA1 gene in HBOC patients. One of the large rearrangement, an amplification of exon 24 in BRCA1, apparently not reported previously, was confirmed by duplex quantitative PCR and array-CGH analysis. Our results, showed that mutations BRCA1 (75%) are more prevalent than BRCA2 (25%) in the Brazilian population. In summary, we reported a comprehensive analysis of the genetic and clinical basis of HBC families in Brazil, which revealed to be highly complex. Currently, a screening for new susceptibility genes using exome sequencing in SOLID platform is under process in 11 non-carriers young (<36 yo) women [5 from this study and 6 from a previous study (Carraro et al., 2013)] revealing new candidates involved in HBC. Citation Format: Marcia Cristina Pena Figueiredo, Felipe Carneiro Silva, Bianca Cristina Garcia Lisboa, Giovana Tardin Torrezan, Elisa Napolitano e Ferreira, Erika Maria Monteiro Santos, Ana Cristina Krepischi, Maria Isabel Waddington Achatz, Benedito Mauro Rossi, Dirce Maria Carraro. Screening for genomic rearrangements and germline mutations in BRCA1 and BRCA2 genes in hereditary breast cancer unrelated Brazilian families. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A025.