Analysis of BRCA1 and BRCA2 mutations in Brazilian breast cancer patients with positive family history

Análise de mutações nos genes BRCA1e BRCA2 em pacientes brasileiros com carcinoma de mama e história familar positiva

ORIGINAL ARTICLE

Analysis of BRCA1 and BRCA2 mutations in Brazilian breast cancer patients with positive family history

Análise de mutações nos genes BRCA1e BRCA2 em pacientes brasileiros com carcinoma de mama e história familar positiva

Rozany Mucha Dufloth; Sílvia Carvalho; Juliana Karina Heinrich; Júlia Yoriko Shinzato; César Cabello dos Santos; Luiz Carlos Zeferino; Fernando Schmitt

Centro de Atenção Integral à Saúde da Mulher, Faculdade de Ciências Médicas da Universidade Estadual de Campinas, Campinas, São Paulo, Brazil, and Institute of Pathology and Molecular Immunology, University of Porto, Porto, Portugal

^{Correspondence}

ABSTRACT

CONTEXT AND OBJECTIVE:BRCA1 and BRCA2 are the two principal hereditary breast cancer susceptibility genes, and the prevalence of their mutations among Brazilian women is unknown. The objective was to detect BRCA1 and BRCA2 mutations in Brazilian patients with breast cancer, so as to establish genetic profiles.

DESIGN AND SETTING: Cross-sectional study, in Centro de Atenção Integral à Saúde da Mulher, Universidade Estadual de Campinas, Brazil, and Institute of Pathology and Molecular Immunology, University of Porto, Portugal.

METHODS: Thirty-one breast cancer patients with positive family history (criteria from the Breast Cancer Linkage Consortium) were studied, and genomic DNA was extracted from peripheral blood. Single-strand conformation polymorphism was used for the analysis of exons 2, 3, 5, and 20 of BRCA1. Cases showing PCR products with abnormal bands were sequenced. Exon 11 of BRCA1 and exons 10 and 11 of BRCA2 were directly sequenced in both directions.

RESULTS: Four mutations were detected: one in BRCA1 and three in BRCA2. The BRCA1 mutation is a frameshift located at codon 1756 of exon 20: 5382 ins C. Two BRCA2 mutations were nonsense mutations located at exon 11: S2219X and the other was an unclassified variant located at exon 11: C1290Y.

CONCLUSION: The BRCA1 or BRCA2 mutation prevalence found among women with breast cancer and such family history was 13% (4/31). Larger studies are needed to establish the significance of BRCA mutations among Brazilian women and the prevalence of specific mutations.

Key words: Breast neoplasms. Hereditary diseases. BRCA1 gene. BRCA2 gene. Base sequence.

RESUMO

CONTEXTO E OBJETIVO:BRCA1 e BRCA2 são os dois principais genes de susceptibilidade ao câncer de mama hereditário e a prevalência de mutações nestes genes não é conhecida em mulheres brasileiras. O objetivo do estudo foi detectar mutações de BRCA1 e BRCA2, contribuindo para estabelecer um perfil dos carcinomas de mama hereditários na população brasileira.

TIPO DE ESTUDO E LOCAL: Estudo transversal, no Centro de Atenção Integral à Saúde da Mulher, Universidade Estadual de Campinas, Brasil, e no Instituto de Patologia e Imunologia Molecular da Universidade do Porto, Portugal.

MÉTODOS: 31 pacientes com carcinoma de mama e história familiar (critérios do Breast Cancer Linkage Consortium), foram estudadas e tiveram DNA extraído do sangue periférico. Single strand conformation polymorphism (SSCP) foi empregado para analisar os exons 2, 3, 5, e 20 do BRCA1. Aqueles casos que mostraram produtos de reação da polimerase em cadeia (PCR) com bandas anormais foram seqüenciados. Entretanto, o exon 11 do BRCA1 e exons 10 e 11 do BRCA2 foram diretamente para o seqüenciamento.

RESULTADOS: Foram identificadas quatro mutações, sendo uma mutação no BRCA1 e três no BRCA2. A mutação no BRCA1 é do tipo frameshift, no exon 20: 5382 insC. Duas mutações encontradas no BRCA2 são do tipo nonsense localizadas no exon 11: S2219X e uma do tipo unclassified variant localizada no exon 11: C1290Y.

CONCLUSÃO: A prevalência de mutações de BRCA1 e BRCA2 encontradas para mulheres com câncer de mama e história familiar de câncer de mama foi de 13% (4/31). Estudos mais amplos são necessários para estabelecer o significado dessas mutações na população brasileira.

Palavras-chave: Câncer da mama. Doenças hereditárias. Gene BRCA1. Gene BRCA2. Seqüências do DNA.

INTRODUCTION

Epidemiological studies have revealed several risk factors associated with increased susceptibility to breast cancer. Among these, familial history is one of the most important. Five to 10% of breast tumors are believed to be hereditary,^1,2 and about 30% of young women who develop breast cancer are likely to show a genetic pattern of predisposition to the disease. This hypothesis is confirmed if these women go on to develop bilateral carcinomas associated with other neoplasias such as carcinoma of the ovary or colon, or if they show an autosomally dominant inheritance pattern.^3,4

In this context, and particularly in high-risk families, the most important tumor suppressor genes associated with breast cancer are BRCA1 and BRCA2. Women who carry BRCA1 mutations have a probability of about 80% for developing breast cancer, and 40 to 60% for developing ovarian cancer during their lifetime.⁵ Moreover, these women have a 65% probability for developing a second breast carcinoma if they reach the age of 70.^6-8 Women who carry BRCA2 mutations have a likelihood of developing breast cancer of about 85%.^6,8,9

BRCA1 is a tumor suppressor gene mapped to position q21 of chromosome 17. It is made up of more than 80 kb, distributed in 22 exons, coding for a protein of 1,863 amino acids.^10,11 Exon 11 comprises 60% of the gene, making it the main target for mutation detection. BRCA2 is another tumor suppressor gene mapping to locus 13q12, comprising 10.4 kb and organized in 27 exons that code for a protein of 3,418 amino acids.^12,13 Mutations in both BRCA1 and BRCA2 are spread throughout the entire gene. More than 600 mutations of BRCA1 and 450 mutations of BRCA2 have been described, according to the Breast Cancer Information Core website (BIC).¹⁴

There are several methods for identifying BRCA mutations. The choice of method depends on the resources available in the laboratory and on the existence of any previously identified mutation in the family or in the patient’s ethnic group, although identification should always be confirmed by sequencing.

The aim of this study was to detect BRCA1 and BRCA2 mutations in a group of Brazilian patients with breast cancer, in an attempt to establish a genetic profile for this population. This information would facilitate BRCA1 and BRCA2 mutational screening in the Brazilian population. Moreover, the detection of mutations in the patient’s family allows identification of individuals at high risk, who are then able to seek genetic counseling.

METHODS

INFORMED CONSENT

Clinical information, pathology reports, slides, paraffin blocks and blood samples were obtained with the informed consent of patients under the guidelines and approval of the Research Ethics Committee of the School of Medical Sciences, Unicamp, and the National Committee for Ethics in Research (Conep).

PATIENT SELECTION

Thirty women and one man with a diagnosis of carcinoma of the breast and a positive family history of breast cancer, who were receiving treatment at the Breast Cancer Outpatient Department of Centro de Atenção Integral à Saúde da Mulher, Universidade Estadual de Campinas (CAISM/Unicamp), Brazil, were identified and invited to participate in this study. The criteria for the identification of individuals at high risk were based on the Breast Cancer Linkage Consortium¹⁵ criteria: early onset (at less than 45 years of age) and/or bilaterality; more than three cases of breast cancer and more than one case of ovarian cancer in the family; more than two first-degree relatives involved; and male breast cancer.

DNA EXTRATION AND MUTATION DETECTON

Genomic DNA was extracted from peripheral blood using the phenol:chloroform method, following a standard protocol.¹⁶ We performed molecular analysis on exons 2, 3, 5, 11 and 20 of the BRCA1 gene and exons 10 and 11 of the BRCA2 gene. For this study, we used single-strand conformation polymorphism and direct sequencing methods.

SINGLE-STRAND CONFORMATION POLYORPHISM

Single-strand conformation polymorphism (SSCP) was used for the analysis of exons 2, 3, 5, and 20 of the BRCA1 gene. The primers used for these exons are described in Table 1. The polymerase chain reaction (PCR) was carried out using 250 ng of DNA, 1 x PCR buffer with 1.5 mM of MgCl₂ (Amersham Biosciences, Piscataway, New Jersey), 200 µM of each dNTP (Amersham Biosciences, as above), 10 rmol of each primer, 1U of Taq DNA polymerase (Amersham Biosciences, as above) at a final volume of 25 µl. The PCR conditions were 96º C for five minutes, then 35 cycles of 30 seconds at 96º C, 30 seconds at the annealing temperature of the primer, 1 minute at 72º C followed by one cycle at 72º C for 10 minutes. For the SSCP analysis, the PCR reaction products were diluted in 1:1 loading buffer (95% formamide, 0.05% bromophenol blue and 0.05% xylene cyanol), and denatured at 98º C for 10 minutes. Electrophoresis of the denatured PCR products was carried out in non-denaturing 0.8 X detection enhancement gels (BMA, Rockland, Maine) at 170 W for 16 hours. In all the cases in which SSCP analysis showed an abnormal electrophoretic pattern, the sample was sequenced in both directions.

DIRECT SEQUENCING

PCR products with abnormal bands in the SSCP pattern were sequenced. In addition, in each patient sample, exon 10 of the BRCA2 gene and 11 of both BRCA genes were directly sequenced in both directions. Exon 11 of the BRCA1 gene was divided into 12 overlapping fragments. Exon 10 of the BRCA2 gene was divided into four overlapping fragments and exon 11 was divided into 16 overlapping fragments (primer sequences are described in Tables 1 and 2). Sequencing was performed by the dideoxy chain termination method, using Big Dye^® technology (Applied Biosystems, Foster City, California). The sequencing primers were the same as those used for PCR. The cycling conditions were as follows: 96º C for five minutes, then 35 cycles of 30 seconds at 94º C, 30 seconds at 51º C, four minutes at 60º C, followed by one 10-minute cycle at 60º C. The products were purified using an MgCl₂/ethanol-based protocol and run on an ABI 3100 sequencer (Applied Biosystems, as above). The results were analyzed using the 3100 data collection software. The sequencing was repeated twice for each sample to rule out the possibility of PCR fidelity artifacts, and was carried out in both directions.

RESULTS

In four cases (13%), changes in the normal sequence of BRCA1 and BRCA2 genes were identified: one of these mutations occurred in the BRCA1 gene and the other three in the BRCA2 gene.

The alteration in exon 20 of BRCA1 was found in a patient who developed breast cancer at the age of 33, and who has a first-degree relative who had also developed the disease. Furthermore, the anatomopathological profile of the carcinoma presented several characteristics that are usually associated with hereditary carcinoma, such as c-erbB2 expression, negativity for hormonal receptors, and high histological grade. Migration alterations were found by SSCP and, after sequencing, a mutation was found in nucleotide 5382, codon 1756 of BRCA1 exon 20. This mutation is referred to as 5382 ins C, according to the BIC database. It is a frameshift mutation that originates in a premature stop codon (STOP 1829) and leads to the formation of a truncated protein (Figure 1).

The BRCA2 mutations were detected in two patients who developed the disease before the age of 45 years and who have at least two second-degree relatives with breast carcinoma. After sequencing, the mutation was localized in exon 11 of BRCA. This is a nonsense mutation originating from a stop codon in nucleotide 6885, referred to as S2219X according to the BIC database (Figure 2).

The other BRCA2 mutation was also found in exon 11 of BRCA2 in a patient who developed the disease at the early age of 29 years, and who had no relatives affected by breast cancer. The mutation is still an unclassified variant according to the BIC database and is referred to as C1290Y, so it is impossible to affirm that it is not a pathogenic mutation (Figure 3).

DISCUSSION

Cloning of the BRCA1¹¹ and BRCA2¹² genes, the major genes known to confer high risk of breast and ovarian cancer, has resulted in the characterization of a large number of mutations in both genes (Breast Cancer Information Core database). Apart from specific ethnic groups, there is no predominant mutation to account for the majority of cases of inherited breast cancer. In some places, recurrent mutations have been described which facilitate the search for mutations in both genes. In spite of the high prevalence of breast cancer in the Brazilian population, there has not been any systematic study of BRCA1 and BRCA2 mutations among breast cancer patients with a family history of the disease.

In the present study, we analyzed 31 breast cancer patients selected according to the criteria adopted by the Breast Cancer Linkage Consortium¹⁵ for hereditary breast cancer. We detected four mutations (13%), one in BRCA1 and three in the BRCA2 gene. The BRCA1 mutation is a frameshift mutation located at codon 1756 of exon 20: 5382 ins C. This mutation has been previously described in Ashkenazi Jews and is clearly associated with an increased risk of breast cancer.¹⁷ The woman with this mutation in the present study developed breast cancer at 33 years of age and she has a first-degree relative with breast cancer. Considering the prevalence of descendants of Ashkenazi Jews in the Brazilian population, it is not surprising to find this mutation in our group of patients.¹⁸

All three BRCA2 mutations found in our study are novel mutations. There were two nonsense mutations located at exon 11: S2219X and one unclassified variant located at exon 11: C1290Y. The S2219X mutation was recently described in a Spanish population from Castilla-Leon.¹⁹ In that study, this mutation was considered to be a novel mutation in the Spanish population. As far as we know, this is the first time that this mutation has been described in the Brazilian population. Although the ancestry of these two patients was specifically investigated, neither of them was found to have Spanish ancestors. Both developed breast cancer before reaching 45 years of age and both had two second-degree relatives with breast cancer.

The method used in the present study, namely direct sequencing, is an expensive technique, but it is the best technique for detecting less frequent mutations and unclassified mutations, as we found in our study sample. Thus, in addition to selecting the patients according to clinical-pathological criteria,²⁰ we should also study specific populations in order to detect recurrent mutations. This may allow us to establish a more cost-effective mutational analysis for this population.

In the present study, most of the mutations detected were novel mutations, which indicates that the mutational screening restricted to prevalent mutations that has previously been reported cannot be recommended in our population. The Brazilian population, like the population of the United States, is ethnically mixed, and founder mutations are therefore rare or even absent. Many European mutations have been observed in the United States and Canada, reflecting European migration to North America. Similarly, in many cases, Central and South American families can trace their origins to the period of Spanish or Portuguese colonization. However, although a previous study in another South American country also demonstrated mutations related to the Ashkenazi Jews,²¹ previous studies carried out by our group among a Portuguese population²² and a Spanish population from Galicia²³ failed to show the mutations that were detected in the present study in the Brazilian population. Further studies are necessary for establishing the relevance of all of these alterations in our population.

This is the first study to investigate BRCA1 and BRCA2 mutations among Brazilian patients with breast cancer. The identification of BRCA1 and BRCA2 mutations is relevant for establishing preventive strategies for women with breast cancer and BRCA mutations, in order to prevent contralateral breast tumors and ovarian tumors. In addition, the detection of mutations in the patient’s family allows identification of individuals at high risk, who can then seek genetic counseling.

CONCLUSION

The prevalence of the BRCA1 or BRCA2 mutation found in this study among women with breast cancer and a family history of breast cancer was 13% (4/31). Large studies are necessary for establishing the significance of the BRCA mutation among Brazilian women and the prevalence of specific mutations. Knowledge of the spectrum of mutations together with their geographical distribution in Brazil is necessary for establishing an effective detection strategy.

Sources of funding: Capes (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior), grant number BEX2448/02-5; Faep (Fundo de Apoio ao Ensino e Pesquisa), Unicamp, grant numbers 1294/02 and 238/04; FLAD (Fundação Luso Americana para o Desenvolvimento), grant number L-V-172/2002.

Conflict of interest: None

Date of first submission: August 6, 2004

Last received: June 6, 2005

Accepted: June 6, 2005

AUTHOR INFORMATION

Rozany Mucha Dufloth, MD, MSc. Centro de Atenção Integral à Saúde da Mulher (CAISM), Faculdade de Ciências Médicas da Universidade Estadual de Campinas (Unicamp), Campinas, São Paulo, Brazil, and Institute of Pathology and Molecular Immunology, University of Porto, Porto, Portugal.

Sílvia Carvalho, BSc. Institute of Pathology and Molecular Immunology, University of Porto, Porto, Portugal.

Juliana Karina Heinrich, MSc. Centro de Atenção Integral à Saúde da Mulher (CAISM), Faculdade de Ciências Médicas da Universidade Estadual de Campinas (Unicamp), Campinas, São Paulo, Brazil.

Júlia Yoriko Shinzato, PhD. Centro de Atenção Integral à Saúde da Mulher (CAISM), Faculdade de Ciências Médicas da Universidade Estadual de Campinas (Unicamp), Campinas, São Paulo, Brazil.

César Cabello dos Santos, MD, PhD. Centro de Atenção Integral à Saúde da Mulher (CAISM), Faculdade de Ciências Médicas da Universidade Estadual de Campinas (Unicamp), Campinas, São Paulo, Brazil.

Luiz Carlos Zeferino, MD, PhD. Centro de Atenção Integral à Saúde da Mulher (CAISM), Faculdade de Ciências Médicas da Universidade Estadual de Campinas (Unicamp), Campinas, São Paulo, Brazil.

Fernando Schmitt, MD, PhD. Institute of Pathology and Molecular Immunology, School of Medicine, University of Porto, Porto, Portugal.

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Publication Dates

• Publication in this collection
  17 Oct 2005
• Date of issue
  2005

History

• Accepted
  06 June 2005
• Reviewed
  06 June 2005
• Received
  06 Aug 2004