Hereditary breast and ovarian cancer: assessment of \ud point mutations and copy number variations in \ud Brazilian patients

Background \ud Germ line mutations in BRCA1 and BRCA2 (BRCA1/2) and other susceptibility genes have \ud been identified as genetic causes of hereditary breast and ovarian cancer (HBOC). To identify \ud the disease-causing mutations in a cohort of 120 Brazilian women fulfilling criteria for \ud HBOC, we carried out a comprehensive screening of BRCA1/2, TP53 R337H, CHEK2 \ud 1100delC, followed by an analysis of copy number variations in 14 additional breast cancer \ud susceptibility genes (PTEN, ATM, NBN, RAD50, RAD51, BRIP1, PALB2, MLH1, MSH2, \ud MSH6, TP53, CDKN2A, CDH1 and CTNNB1). \ud Methods \ud Capillary sequencing and multiplex ligation-dependent probe amplification (MLPA) were \ud used for detecting point mutations and copy number variations (CNVs), respectively, for the \ud BRCA1 and BRCA2 genes; capillary sequencing was used for point mutation for both variants \ud TP53 R337H and CHEK2 1100delC, and finally array comparative genomic hybridization \ud (array-CGH) was used for identifying CNVs in the 14 additional genes. \ud Results \ud The positive detection rate in our series was 26%. BRCA1 pathogenic mutations were found \ud in 20 cases, including two cases with CNVs, whereas BRCA2 mutations were found in 7 \ud cases. We also found three patients with the TP53 R337H mutation and one patient with the \ud CHEK2 1100delC mutation. Seven (25%) pathogenic mutations in BRCA1/2 were firstly \ud described, including a splice-site BRCA1 mutation for which pathogenicity was confirmed by \ud the presence of an aberrant transcript showing the loss of the last 62 bp of exon 7. \ud Microdeletions of exon 4 in ATM and exon 2 in PTEN were identified in BRCA2-mutated and \ud BRCA1/2-negative patients, respectively. \ud Conclusions \ud In summary, our results showed a high frequency of BRCA1/2 mutations and a higher \ud prevalence of BRCA1 (64.5%) gene. Moreover, the detection of the TP53 R337H variant in \ud our series and the fact that this variant has a founder effect in our population prompted us to \ud suggest that all female breast cancer patients with clinical criteria for HBOC and negative for \ud BRCA1/2 genes should be tested for the TP53 R337H variant. Furthermore, the presence of \ud genomic structural rearrangement resulting in CNVs in other genes that predispose breast \ud cancer in conjunction with BRCA2 point mutations demonstrated a highly complex genetic \ud etiology in Brazilian breast cancer families.Fundação de Amparo à Pesquisa do Estado de São Paulo (2008/57887- 9).Conselho Nacional de Desenvolvimento Científico e Tecnológico (408833/2006-8