Câncer de mama hereditário: rastreamento de mutações nos genes BRCA1 e BRCA2 e busca de novos genes de susceptibilidade / Hereditary breast cancer: screening for mutations in the BRCA1 and BRCA2 genes and search for new susceptibility genes

RESUMO

O Câncer de Mama Hereditário (HBC) é uma doença autossômica dominante caracterizada, principalmente, por mutações germinativas nos genes BRCA1 e BRCA2 que conferem alto risco em desenvolver câncer de mama e ovário. A identificação da causa genética responsável pelo aumento de risco em mulheres com critérios clínicos para HBC é extremamente importante para o manejo das mesmas. Dessa forma, o objetivo do presente estudo foi avaliar mutações pontuais germinativas e alterações no número de cópias (CNV) nos genes BRCA1 e BRCA2 em 128 famílias brasileiras, as quais preencheram os seguintes critérios para HBC 108 para Câncer de Mama e Ovário Hereditário (HBOC), 20 para Câncer de Mama e Colón Hereditário (HBCC), sendo que 32 preencheram critérios clínicos para ambos. Amostras de DNA de sangue periférico foram utilizadas para avaliar a presença de mutações germinativas através do sequenciamento completo dos genes BRCA1 e BRCA2 nas sequências codificadoras e limites éxon-íntron e também verificar as mutações pontuais nos genes TP53 (R337H) e CHEK2 (1100delC). Os pacientes não portadores de mutações nos genes BRCA1/2 foram selecionados para análise de MLPA (multiplex ligation-dependent probe amplification) para avaliar as CNVs nestes genes. A prevalência de mutações patogênicas neste estudo foi de 25% (32/128), incluindo 21 no BRCA1 (2 splice site, 2 missense, 9 frameshift, 6 nonsense e 2 CNVs), 7 no BRCA2 (3 frameshift e 4 nonsense), 3 no TP53 (3 missense) e uma no gene CHEK2 (1100delC). Sete (25% - 7/28) das mutações patogênicas identificadas nos genes BRCA1 e BRCA2 foram descritas pela primeira vez neste estudo, cinco no gene BRCA1, incluindo uma nova mutação no sítio de splice no BRCA1, cuja patogenicidade foi confirmada através da análise do transcrito; e duas no gene BRCA2...

ABSTRACT

Hereditary Breast Cancer (HBC) is an autosomal dominant disease mainly characterized by germline mutations in BRCA1 and BRCA2 genes that confer high risk for developing breast and ovarian cancer. The identification of high-risk women carrying mutations responsible for the disease is extremely important for their management. Thus, the aim of this study was to evaluate germline mutations and copy number variations (CNVs), in BRCA1 and BRCA2 in 128 Brazilian families, who met the following criteria for HBC 108 for Hereditary Breast and Ovarian Cancer (HBOC) and 20 for Hereditary Breast and Colon Cancer (HBCC). Thirty two patients met clinical criteria for both syndromes. DNA samples from peripheral blood were used to assess the presence of germline mutations by capillary sequencing of the entire coding sequence of BRCA1 and BRCA2 genes, exon - intron boundaries, as well as TP53 (R337H) and CHEK2 (1100delC) variants. Patients who did not carry mutations in the BRCA1/2 genes were selected for MLPA analysis (multiplex ligation-dependent probe amplification) to assess CNVs in these genes. The prevalence of pathogenic mutations in this study were 25 % (32 /128) , including 21 in BRCA1 (2 splice site, 2 missense, 9 frameshift, 6 nonsense and 2 CNVs), 7 BRCA2 (3 nonsense and 4 frameshift ), 3 in TP53 (3 missense) and one in CHEK2 gene. Seven (25 % - 7/28) out of 28 pathogenic mutations in BRCA1 and BRCA2 genes were first described in this study, of which five were in the BRCA1, including a novel splice site mutation, whose pathogenicity was confirmed by transcript analysis and two in the BRCA2 gene. Among the VUS carriers 18 different were found variants, where two of them were described for the first time. The analysis of the three algorithms for protein prediction of VUS ( Polyphen, SIFT and AlignGVGD) showed that seven variants have been classified as probably pathogenic in at least one of them (four in one algorithm , two in two algorithms and one...