乳腺癌与卵巢癌易感基因BRCA1和BRCA2

BRCA1和BRCA2是近年来发现的遗传性乳腺癌和卵巢癌易感基因,分别位于第17号和第13号染色体上。目前所知,两者与细胞周期调控、胚胎生 长发育、DNA损伤修复和转录调控等生命活动有关。随着BRCA1和BRCA2研究的不断深入和其确切生物学功能的阐明,将在临床上帮助早期诊断和有效治疗乳腺癌和卵巢癌患者。     

肿瘤易感基因BRCA1

ＢＲＣＡ１为一新的肿瘤易感基因，定位在１７ｑ２１，其ｃＤＮＡ可转录７．８ｋｂｍＲＮＡ，编码含１８６３个氨基酸残基的长多态，在遣传性乳腺卵巢癌中有高频率的ＢＲＣＡ１基因杂合性丢失，同时有多形式多位点的基因突变，符合肿瘤抑制基因特点。     

110例维吾尔族及汉族乳腺癌中BRCA1基因突变及P53蛋白表达的研究

目的研究维吾尔族及汉族乳腺癌患者BRCA1基因突变及P53蛋白的表达。方法选取70例维吾尔族和40例汉族乳腺癌根治标本,对照组为32例维汉族乳腺良性病变(纤维腺病及纤维腺瘤)及乳腺癌旁非癌组织;运用PCR-SSCP和DNA序列测定的方法检测BRCA1基因突变及Evision二步法检测P53蛋白的表达。结果(1)110例维吾尔族及汉族乳腺癌中发现BRCA1突变的14个新位点。(2)110例维吾尔族及汉族乳腺癌BRCA1的突变率为10%,其中22例维吾尔族早发性乳腺癌(≤35岁)BRCA1突变率为31.82%,高于维吾尔族晚发性乳腺癌(P<0.01)。(3)110例维吾尔族及汉族乳腺癌中发现11例BRCA1基因核苷酸多态性位点。(4)BRCA1基因突变相关性乳腺癌中P53蛋白阳性表达率高于对照组,其淋巴结转移率高于对照组,其发病年龄小于对照组(P<0.01)。结论BRCA1基因突变与新疆维吾尔族早发性乳腺癌密切相关,且BRCA1突变相关性乳腺癌具有P53阳性率高、发病年龄趋于年轻化、淋巴结转移率高的趋势,这些特点有可能为基因检测前的筛选提供参考依据。     

BRCA1和BRCA2与DNA损伤修复及转录调控

乳腺癌和卵巢癌敏感基因BRCA1和BRCA2与同源重组,DNA损伤修复,胚胎生长,转录调控及遍在蛋白化有关,其中,BRCA1和BRCA2在DNA损伤修复和转录调控中功能的确定,将有助于探讨和阐明两者的肿瘤抑制功能及其机理,作者将综述近年来有关BRCA1和BRCA2在DNA损伤修复和转录调控中功能研究的最新进展。     

BRCA1基因与乳腺癌

乳腺癌易感基因1(BRCA1)是具有遗传倾向的乳腺癌和卵巢癌的易感基因,且是一种抑癌基因.BRCA1基因的突变与家族性乳腺癌及它在细胞周期的调节,DNA损伤修复,基因的转录调控和诱导细胞凋亡方面起着重要作用.BRCA1基因的突变与家族性乳腺癌及卵巢癌的发生密切相关,对BRCA1分子功能的研究,将有利于阐明肿瘤发生的机理关.BRCA1的启动子甲基化与散发性乳腺癌有关.本文拟对BRCA1的结构,功能以及它的甲基化,突变,杂合性丢失对乳腺癌的影响作一综述.     

乳腺癌易感基因BRCA1研究进展

BRCA1是目前所发现的最重要的乳腺癌易感基因之一,它在DNA损伤修复,细胞周期调节,基因的转录激活,染色质稳定性,细胞增殖等方面都起着重要作用。该文着重介绍近几年来BRCA1基础研究方面的进展,并讨论BRCA1在肿瘤发生、发展过程的作用。为BRCA1在临床上的应用提供理论依据。     

乳腺癌易感基因BRCA1的研究进展

BRCA1基因是目前发现的外显率最高的乳腺癌易感基因之,编码一个相对分子质量为220000的多功能核蛋白,作用于一系列维持基因组稳定性的细胞通路,包括DNA损伤修复、细胞周期检验点激活、蛋白泛素化、染色质重组,以及转录调控和凋亡等。BRCA1丢失将导致显著的遗传不稳定性和生长停滞。着重介绍近年来BRCA1基础研究方面的进展,并讨论BRCA1与乳腺癌的临床关联性。     

BRCA1 基因启动子区SNPs 与散发性乳腺癌易感性的相关研究

目的:探讨BRCA1基因启动子区rs11655505、rs73625095位点单核苷酸多态性与散发性乳腺癌易感性的关系。方法:采用ASA-PCR方法对200例乳腺癌患者(均经病理确诊)及200例正常女性BRCA1基因启动子区rs11655505(A/G)、rs73625095(A/G)位点单核苷酸多态性(SNP)进行分析,并将其PCR产物进行测序。结果:乳腺癌患者BRCA1基因启动子区rs11655505位点的A/G基因型频率为75%,显著高于正常人的40%;A/A基因型频率为7%,G/G基因型频率为18%,分别低于正常人的30%、30%。此位点的A或G等位基因在乳腺癌病例组及对照组中均无差别(x2=2.427,P=0.119);rs73625095位点的A/G基因型频率为68%,显著高于正常人的15%;G/G基因型频率为32%,低于正常人的84%;乳腺癌病例组中BRCA1基因启动子区rs11655505、rs73625095位点的A/G基因型与淋巴结转移与否相比,差别均有统计学意义(x2=7.321,P=0.026、x2=4.782,P=0.029)。结论:BRCA1基因rs11655505位点、rs736...     

BRCA1基因启动子区SNPs与散发性乳腺癌易感性的相关研究（英文）

目的：探讨BRCA1基因启动子区rs11655505、rs73625095位点单核苷酸多态性与散发性乳腺癌易感性的关系。方法：采用ASA-PCR方法对200例乳腺癌患者（均经病理确诊）及200例正常女性BRCA1基因启动子区rs11655505（A/G）、rs73625095（A/G）位点单核苷酸多态性（SNP）进行分析,并将其PCR产物进行测序。结果：乳腺癌患者BRCA1基因启动子区rs11655505位点的A/G基因型频率为75%,显著高于正常人的40%;A/A基因型频率为7%,G/G基因型频率为18%,分别低于正常人的30%、30%。此位点的A或G等位基因在乳腺癌病例组及对照组中均无差别（x2=2.427,P=0.119）;rs73625095位点的A/G基因型频率为68%,显著高于正常人的15%;G/G基因型频率为32%,低于正常人的84%;乳腺癌病例组中BRCA1基因启动子区rs11655505、rs73625095位点的A/G基因型与淋巴结转移与否相比,差别均有统计学意义（x2=7.321,P=0.026、x2=4.782,P=0.029）。结论：BRCA1基因rs11655505位点、rs73625095位点的A/G基因型可能与散发性乳腺癌的发生相关,而且与有无发生淋巴结转移密切相关。rs73625095位点A和G等位基因可能为散发性乳腺癌发生的遗传危险因素。     

家族性乳腺癌和健康遗传高危人群BRCA1/2基因突变研究

目的:研究中国汉族女性家族性乳腺癌患者和健康遗传性高危人群的BRCA1/2基因突变特征。方法:研究对象为2013年12月~2014年10月于解放军307医院乳腺外科确诊的54例汉族家族性乳腺癌患者及24例健康遗传性高危人群,应用PCR-DNA直接测序法检测乳腺癌易感基因BRCA1和BRCA2的全编码外显子基因序列。结果:54例家族性乳腺癌患者中共发现8例致病性突变,突变类型均为单个碱基置换,BRCA1和BRCA2的总突变率为14.8%,BRCA1突变率为11.1%,BRCA2突变率为3.7%;其中,三阴性乳腺癌患者BRCA总突变率高于非三阴性乳腺癌患者的总突变率(28.6%vs 12.8%),差异具有统计学意义(P0.05)。24例遗传性高危人群中共发现2例致病性突变,均为BRCA1基因突变,突变率为8.3%。结论:用BRCA1/2突变检测"金标准"的一代测序法再次发现在中国汉族女性家族性乳腺癌中存在的BRCA1/2突变,与三阴性乳腺癌有关,并发现碱基置换突变也是重要的突变类型;在健康遗传性高危人群中存在一定比例的BRCA1突变,值得关注。     

Detection of New Point Mutations of BRCA1 and BRCA2 in Breast Cancer Patients

This study included 20 selected female patients with breast cancer, 30 of their female relatives (sisters and daughters), and 10 healthy females as a control group. Genomic DNA was extracted from peripheral blood lymphocytes of all the subjects, and the polymerase chain reaction was carried out using specific primers for BRCA1 (exons 2 and 8) and BRCA2 (exons 9, 11, and 21). The mutations were detected using a single-strand conformation polymorphism assay and heteroduplex analysis. Finally, the sample variants and their controls were sequenced. Mutations were detected in 44% of the study population, with 18% found in the BRCA1 gene and 26% attributed to BRCA2. Five sequence variants were identified, including two frameshift mutations, one nonsense mutation, and two missense mutations. Therefore, we conclude that germline mutations in two major genes, BRCA1 and BRCA2, may have an important influence on the predisposition and development of familial breast cancer.     

Copy Number Variation Analysis in Familial BRCA1/2-Negative Finnish Breast and Ovarian Cancer

Background

Inherited factors predisposing individuals to breast and ovarian cancer are largely unidentified in a majority of families with hereditary breast and ovarian cancer (HBOC). We aimed to identify germline copy number variations (CNVs) contributing to HBOC susceptibility in the Finnish population.

Methods

A cohort of 84 HBOC individuals (negative for BRCA1/2-founder mutations and pre-screened for the most common breast cancer genes) and 36 healthy controls were analysed with a genome-wide SNP array. CNV-affecting genes were further studied by Gene Ontology term enrichment, pathway analyses, and database searches to reveal genes with potential for breast and ovarian cancer predisposition. CNVs that were considered to be important were validated and genotyped in 20 additional HBOC individuals (6 CNVs) and in additional healthy controls (5 CNVs) by qPCR.

Results

An intronic deletion in the EPHA3 receptor tyrosine kinase was enriched in HBOC individuals (12 of 101, 11.9%) compared with controls (27 of 432, 6.3%) (OR = 1.96; P = 0.055). EPHA3 was identified in several enriched molecular functions including receptor activity. Both a novel intronic deletion in the CSMD1 tumor suppressor gene and a homozygous intergenic deletion at 5q15 were identified in 1 of 101 (1.0%) HBOC individuals but were very rare (1 of 436, 0.2% and 1 of 899, 0.1%, respectively) in healthy controls suggesting that these variants confer disease susceptibility.

Conclusion

This study reveals new information regarding the germline CNVs that likely contribute to HBOC susceptibility in Finland. This information may be used to facilitate the genetic counselling of HBOC individuals but the preliminary results warrant additional studies of a larger study group.     

Prevalence of BRCA1 Mutations in Familial and Sporadic Greek Ovarian Cancer Cases

Germline mutations in the BRCA1 and BRCA2 genes contribute to approximately 18% of hereditary ovarian cancers conferring an estimated lifetime risk from 15% to 50%. A variable incidence of mutations has been reported for these genes in ovarian cancer cases from different populations. In Greece, six mutations in BRCA1 account for 63% of all mutations detected in both BRCA1 and BRCA2 genes. This study aimed to determine the prevalence of BRCA1 mutations in a Greek cohort of 106 familial ovarian cancer patients that had strong family history or metachronous breast cancer and 592 sporadic ovarian cancer cases. All 698 patients were screened for the six recurrent Greek mutations (including founder mutations c.5266dupC, p.G1738R and the three large deletions of exon 20, exons 23–24 and exon 24). In familial cases, the BRCA1 gene was consequently screened for exons 5, 11, 12, 20, 21, 22, 23, 24. A deleterious BRCA1 mutation was found in 43/106 (40.6%) of familial cancer cases and in 27/592 (4.6%) of sporadic cases. The variant of unknown clinical significance p.V1833M was identified in 9/698 patients (1.3%). The majority of BRCA1 carriers (71.2%) presented a high-grade serous phenotype. Identifying a mutation in the BRCA1 gene among breast and/or ovarian cancer families is important, as it enables carriers to take preventive measures. All ovarian cancer patients with a serous phenotype should be considered for genetic testing. Further studies are warranted to determine the prevalence of mutations in the rest of the BRCA1 gene, in the BRCA2 gene, and other novel predisposing genes for breast and ovarian cancer.     

Identification of BRCA1/2 Founder Mutations in Southern Chinese Breast Cancer Patients Using Gene Sequencing and High Resolution DNA Melting Analysis

Background

Ethnic variations in breast cancer epidemiology and genetics have necessitated investigation of the spectra of BRCA1 and BRCA2 mutations in different populations. Knowledge of BRCA mutations in Chinese populations is still largely unknown. We conducted a multi-center study to characterize the spectra of BRCA mutations in Chinese breast and ovarian cancer patients from Southern China.

Methodology/Principal Findings

A total of 651 clinically high-risk breast and/or ovarian cancer patients were recruited from the Hong Kong Hereditary Breast Cancer Family Registry from 2007 to 2011. Comprehensive BRCA1 and BRCA2 mutation screening was performed using bi-directional sequencing of all coding exons of BRCA1 and BRCA2. Sequencing results were confirmed by in-house developed full high resolution DNA melting (HRM) analysis. Among the 451 probands analyzed, 69 (15.3%) deleterious BRCA mutations were identified, comprising 29 in BRCA1 and 40 in BRCA2. The four recurrent BRCA1 mutations (c.470_471delCT, c.3342_3345delAGAA, c.5406+1_5406+3delGTA and c.981_982delAT) accounted for 34.5% (10/29) of all BRCA1 mutations in this cohort. The four recurrent BRCA2 mutations (c.2808_2811delACAA, c.3109C>T, c.7436_7805del370 and c.9097_9098insA) accounted for 40% (16/40) of all BRCA2 mutations. Haplotype analysis was performed to confirm 1 BRCA1 and 3 BRCA2 mutations are putative founder mutations. Rapid HRM mutation screening for a panel of the founder mutations were developed and validated.

Conclusion

In this study, our findings suggest that BRCA mutations account for a substantial proportion of hereditary breast/ovarian cancer in Southern Chinese population. Knowing the spectrum and frequency of the founder mutations in this population will assist in the development of a cost-effective rapid screening assay, which in turn facilitates genetic counseling and testing for the purpose of cancer risk assessment.     

BRCA Mutations Increase Fertility in Families at Hereditary Breast/Ovarian Cancer Risk

Background

Deleterious mutations in the BRCA genes are responsible for a small, but significant, proportion of breast and ovarian cancers (5 - 10 %). Proof of de novo mutations in hereditary breast/ovarian cancer (HBOC) families is rare, in contrast to founder mutations, thousands of years old, that may be carried by as much as 1 % of a population. Thus, if mutations favoring cancer survive selection pressure through time, they must provide advantages that compensate for the loss of life expectancy.

Method

This hypothesis was tested within 2,150 HBOC families encompassing 96,325 individuals. Parameters included counts of breast/ovarian cancer, age at diagnosis, male breast cancer and other cancer locations. As expected, well-known clinical parameters discriminated between BRCA-mutated families and others: young age at breast cancer, ovarian cancer, pancreatic cancer and male breast cancer. The major fertility differences concerned men in BRCA-mutated families: they had lower first and mean age at paternity, and fewer remained childless. For women in BRCA families, the miscarriage rate was lower. In a logistic regression including clinical factors, the different miscarriage rate and men''s mean age at paternity remained significant.

Results

Fertility advantages were confirmed in a subgroup of 746 BRCA mutation carriers and 483 non-carriers from BRCA mutated families. In particular, female carriers were less often nulliparous (9.1 % of carriers versus 16.0 %, p = 0.003) and had more children (1.8 ± 1.4 SD versus 1.5 ± 1.3, p = 0.002) as well as male carriers (1.7 ± 1.3 versus 1.4 ± 1.3, p = 0.024).

Conclusion

Although BRCA mutations shorten the reproductive period due to cancer mortality, they compensate by improving fertility both in male and female carriers.     

Tumor Mutation Burden Forecasts Outcome in Ovarian Cancer with BRCA1 or BRCA2 Mutations

Background

Increased number of single nucleotide substitutions is seen in breast and ovarian cancer genomes carrying disease-associated mutations in BRCA1 or BRCA2. The significance of these genome-wide mutations is unknown. We hypothesize genome-wide mutation burden mirrors deficiencies in DNA repair and is associated with treatment outcome in ovarian cancer.

Methods and Results

The total number of synonymous and non-synonymous exome mutations (Nmut), and the presence of germline or somatic mutation in BRCA1 or BRCA2 (mBRCA) were extracted from whole-exome sequences of high-grade serous ovarian cancers from The Cancer Genome Atlas (TCGA). Cox regression and Kaplan-Meier methods were used to correlate Nmut with chemotherapy response and outcome. Higher Nmut correlated with a better response to chemotherapy after surgery. In patients with mBRCA-associated cancer, low Nmut was associated with shorter progression-free survival (PFS) and overall survival (OS), independent of other prognostic factors in multivariate analysis. Patients with mBRCA-associated cancers and a high Nmut had remarkably favorable PFS and OS. The association with survival was similar in cancers with either BRCA1 or BRCA2 mutations. In cancers with wild-type BRCA, tumor Nmut was associated with treatment response in patients with no residual disease after surgery.

Conclusions

Tumor Nmut was associated with treatment response and with both PFS and OS in patients with high-grade serous ovarian cancer carrying BRCA1 or BRCA2 mutations. In the TCGA cohort, low Nmut predicted resistance to chemotherapy, and for shorter PFS and OS, while high Nmut forecasts a remarkably favorable outcome in mBRCA-associated ovarian cancer. Our observations suggest that the total mutation burden coupled with BRCA1 or BRCA2 mutations in ovarian cancer is a genomic marker of prognosis and predictor of treatment response. This marker may reflect the degree of deficiency in BRCA-mediated pathways, or the extent of compensation for the deficiency by alternative mechanisms.     

DHPLC/SURVEYOR Nuclease: A Sensitive, Rapid and Affordable Method to Analyze BRCA1 and BRCA2 Mutations in Breast Cancer Families

Hereditary breast cancer accounts for about 10% of all breast cancers and BRCA1 and BRCA2 genes have been identified as validated susceptibility genes for this pathology. Testing for BRCA gene mutations is usually based on a pre-screening approach, such as the partial denaturation DHPLC method, and capillary direct sequencing. However, this approach is time consuming due to the large size of BRCA1 and BRCA2 genes. Recently, a new low cost and time saving DHPLC protocol has been developed to analyze gene mutations by using SURVEYOR(?) Nuclease digestion and DHPLC analysis. A subset of 90 patients, enrolled in the Genetic Counseling Program of the National Cancer Centre of Bari (Italy), was performed to validate this approach. Previous retrospective analysis showed that 9/90 patients (10%) were mutated in BRCA1 and BRCA2 genes and these data were confirmed by the present approach. DNA samples underwent touchdown PCR and, subsequently, SURVEYOR(?) nuclease digestion. BRCA1 and BRCA2 amplicons were divided into groups depending on amplicon size to allow multiamplicon digestion. The product of this reaction were analyzed on Transgenomic WAVE Nucleic Acid High Sensitivity Fragment Analysis System. The operator who performed the DHPLC surveyor approach did not know the sequencing results at that time. The SURVEYOR(?) Nuclease DHPLC approach was able to detect all alterations with a sensitivity of 95%. Furthermore, in order to save time and reagents, a multiamplicon setting preparation was validated.     

Analysis of PALB2 Gene in BRCA1/BRCA2 Negative Spanish Hereditary Breast/Ovarian Cancer Families with Pancreatic Cancer Cases

Background

The PALB2 gene, also known as FANCN, forms a bond and co-localizes with BRCA2 in DNA repair. Germline mutations in PALB2 have been identified in approximately 1% of familial breast cancer and 3–4% of familial pancreatic cancer. The goal of this study was to determine the prevalence of PALB2 mutations in a population of BRCA1/BRCA2 negative breast cancer patients selected from either a personal or family history of pancreatic cancer.

Methods

132 non-BRCA1/BRCA2 breast/ovarian cancer families with at least one pancreatic cancer case were included in the study. PALB2 mutational analysis was performed by direct sequencing of all coding exons and intron/exon boundaries, as well as multiplex ligation-dependent probe amplification.

Results

Two PALB2 truncating mutations, the c.1653T>A (p.Tyr551Stop) previously reported, and c.3362del (p.Gly1121ValfsX3) which is a novel frameshift mutation, were identified. Moreover, several PALB2 variants were detected; some of them were predicted as pathological by bioinformatic analysis. Considering truncating mutations, the prevalence rate of our population of BRCA1/2-negative breast cancer patients with pancreatic cancer is 1.5%.

Conclusions

The prevalence rate of PALB2 mutations in non-BRCA1/BRCA2 breast/ovarian cancer families, selected from either a personal or family pancreatic cancer history, is similar to that previously described for unselected breast/ovarian cancer families. Future research directed towards identifying other gene(s) involved in the development of breast/pancreatic cancer families is required.