Identification of the 185delAG BRCA1 mutation in a Spanish Gypsy population

The 185delAG BRCA1 deletion occurs with a high frequency in Ashkenazi Jews. We detected this mutation in two Spanish Gypsy women (the only Gypsy participants) in an extensive study of 90 high-risk families and 160 women with early-onset breast cancer. One of these Gypsy women belonged to a high-risk family and the other had had early-onset breast cancer. The mutation was also detected in 1 out of 25 Gypsy samples unrelated to breast cancer. All the samples with the mutation shared the marker alleles present in Jewish samples with 185delAG. This is the first report of this mutation in a non-Jewish well-defined ethnic population. According to these findings the carrier frequency of this mutation in Gypsy individuals could be several times higher than that of the general population, and this should be taken into consideration in genetic screening for cancer in Gypsy populations. Received: 2 August 1998 / Accepted: 9 October 1998     

BRCA1 185delAG mutation inhibits Akt-dependent, IAP-mediated caspase 3 inactivation in human ovarian surface epithelial cells

BRCA1 mutations have long been associated with altered apoptosis. We have recently reported that caspase 3 activation is increased in human ovarian surface epithelial (OSE) cells expressing a germline N-terminal BRCA1 185delAG mutation. Here, we report increased caspase 3 activity in 185delAG OSE cells associated with decreased expression of cIAP-1 and X-linked inhibitor of apoptosis (XIAP), and decreased ubiquitination of caspase 3. Overexpression of XIAP restored active caspase 3 ubiquitination and lowered levels of caspase 3 activity. Further, the BRCA1 185delAG mutation was associated with reduced levels of phosphorylated Akt1. Transfection with activated Akt1 led to increased cIAP-1 and XIAP levels similar to that seen in BRCA1 185delAG cell lines. Taken together, these data suggest a direct link between the BRCA1 185delAG mutation and alterations in the caspase-mediated apoptotic pathway.     

Prevalence of 185delAG and 5382insC mutations in BRCA1, and 6174delT in BRCA2 in women of Ashkenazi Jewish origin in southern Brazil

Certain mutations in BRCA1 and BRCA2 genes are frequent in the Ashkenazi Jewish population. Several factors contribute to this increased frequency, including consanguineous marriages and an event known as a “bottleneck”, which occurred in the past and caused a drastic reduction in the genetic variability of this population. Several studies were performed over the years in an attempt to elucidate the role of BRCA1 and BRCA2 genes in susceptibility to breast cancer. The aim of this study was to estimate the carrier frequency of certain common mutations in the BRCA1 (185delAG and 5382insC) and BRCA2 (6174delT) genes in an Ashkenazi Jewish population from Porto Alegre, Brazil. Molecular analyses were done by PCR followed by RFLP (ACRS). The carrier frequencies for BRCA1 185delAG and 5382insC were 0.78 and 0 respectively, and 0.4 for the BRCA2 6174deT mutation. These findings are similar to those of some prior studies but differ from others, possibly due to excluding individuals with a personal or family history of cancer. Our sample was drawn from the community group and included individuals with or without a family or personal history of cancer. Furthermore, increased dispersion among Ashkenazi subpopulations may be the result of strong genetic drift and/or admixture. It is therefore necessary to consider the effects of local admixture on the mismatch distributions of various Jewish populations.     

Screening for 185delAG in the Ashkenazim.

A study was initiated to assess interest, educational effectiveness, and implications of genetic testing for the common BRCA1 mutation, 185delAG, in the Ashkenazim. Of 333 individuals who attended group sessions, 309 (92%) participated in the study. Participants were categorized as having negative family history (67%), positive family history (defined, by a relaxed criterion, as one first-degree relative or two second-degree relatives with breast [premenopausal] or ovarian cancer) (22%), positive personal history (7%), and both positive personal history and positive family history (4%). Group education was effective, as shown by the improvement in participant scores from pre- to posteducation tests. For the 289 individuals (94%) who requested testing, the major reasons included concern for their own risk, concern for the risk of their children, and desire to learn about surveillance options. The most common reason given by participants who declined testing was concern about health insurance. Six participants found to be heterozygous for the 185delAG mutation received results and were offered genetic counseling. Participants had consented for additional testing without receiving results and were screened for the 6174delT mutation in BRCA2, and seven were found to be positive. All identified carriers reported at least one first- or second-degree relative with a history of breast or ovarian cancer, although they did not all meet our study criteria for positive family history. Given these outcomes, we conclude that screening for breast and ovarian cancer susceptibility is most appropriate for individuals with a positive personal or positive family cancer history. We propose a guideline for future studies designed to identify individuals who may benefit from genetic testing for inherited breast and ovarian cancer.     

Haplotype analysis of BRCA2 8765delAG mutation carriers in French Canadian and Yemenite Jewish hereditary breast cancer families

The BRCA2 8765delAG mutation was previously reported in hereditary breast cancer families of French Canadian and Yemenite Jewish descent. Haplotype analysis, using six microsatellite markers that span BRCA2 and two intragenic polymorphisms, was performed on 8765delAG mutation carriers to determine if there was evidence that the mutations were identical by descent. The alleles of the microsatellite markers most closely flanking BRCA2 (D13S1697 and D13S1701) were found to be identical in state in all the mutation carriers. However, the disease-associated allele of one of the intragenic markers differed between the Yemenite Jews and French Canadian families, indicating that the 8765delAG mutation has independent origins in these two geographically and ethnically distinct populations.     

Mutation detection in the breast cancer gene BRCA1 using the protein truncation test

About 400 distinct mutations have been defined in the BRCA1 gene, and these are spread fairly evenly through the 5592 bp of coding DNA. This circumstance presents a formidable challenge for mutation screening. Apart from total direct sequencing, the preferred screening method has been single-strand conformation polymorphism (SSCP) gels, with a smaller input from constant denaturant gradient electrophoresis (CDGE), heteroduplex (HD) analysis, and mismatch cleavage. The protein truncation test (PTT) was used early in BRCA1 mutation screening but has not been widely adopted, perhaps because a straightforward analysis of the whole BRCA1 gene requires working with RNA and all its perceived problems. The present work was undertaken to assess the practicality of using the PTT under routine conditions for the screening of long genes such as BRCA1 that are not highly expressed in lymphocytes. We conclude that, provided RNA preparation is carried out effectively and consistently, the PTT approach has significant advantages over other methodologies such as SSCP gels.     

Detection of protein folding defects caused by BRCA1-BRCT truncation and missense mutations

Most cancer-associated BRCA1 mutations identified to date result in the premature translational termination of the protein, highlighting a crucial role for the C-terminal, BRCT repeat region in mediating BRCA1 tumor suppressor function. However, the molecular and genetic effects of missense mutations that map to the BRCT region remain largely unknown. Using a protease-based assay, we directly assessed the sensitivity of the folding of the BRCT domain to an extensive set of truncation and single amino acid substitutions derived from breast cancer screening programs. The protein can tolerate truncations of up to 8 amino acids, but further deletion results in drastic BRCT folding defects. This molecular phenotype can be correlated with an increased susceptibility to disease. A cross-validated computational assessment of the BRCT mutation data base suggests that as much as half of all BRCT missense mutations contribute to BRCA1 loss of function and disease through protein-destabilizing effects. The coupled use of proteolytic methods and computational predictive methods to detect mutant BRCA1 conformations at the protein level will augment the efficacy of current BRCA1 screening protocols, especially in the absence of clinical data that can be used to discriminate deleterious BRCT missense mutations from benign polymorphisms.     

Loss of nuclear BRCA1 protein staining in normal tissue cells derived from BRCA1 and BRCA2 mutation carriers

Enhanced genomic instability has been recently reported in normal cells derived from BRCA1/2 mutation carriers when placed in vitro in non-physiological stress conditions. We present here original data which help to explain the observed genomic instability. Leucocytes from BRCA1/2 mutation carriers, sporadic breast cancer patients and controls were prepared for BRCA1 immunocytochemistry. We show that BRCA1 containing nuclear dot like structures are detectable in about 80% of the leucocytes from controls and sporadic breast cancer patients, but are absent in the majority of normal cells from BRCA1 as well as BRCA2 mutation carriers (also in their normal breast cells). Our results thus indicate that the genomic instability observed in normal cells from BRCA1 and BRCA2 mutation carriers is associated with a down-regulation of nuclear BRCA1 protein accumulation in the dot like structures. These results suggest in addition that immunocytochemical or alternative molecular screening strategies might help to identify women with a high risk for breast (ovarian) cancer even when the underlying genetic defect remains undetectable.     

BRCA1 and BRCA2 mutation analysis of 208 Ashkenazi Jewish women with ovarian cancer

Ovarian cancer is a component of the autosomal-dominant hereditary breast-ovarian cancer syndrome and may be due to a mutation in either the BRCA1 or BRCA2 genes. Two mutations in BRCA1 (185delAG and 5382insC) and one mutation in BRCA2 (6174delT) are common in the Ashkenazi Jewish population. One of these three mutations is present in approximately 2% of the Jewish population. Each mutation is associated with an increased risk of ovarian cancer, and it is expected that a significant proportion of Jewish women with ovarian cancer will carry one of these mutations. To estimate the proportion of ovarian cancers attributable to founding mutations in BRCA1 and BRCA2 in the Jewish population and the familial cancer risks associated with each, we interviewed 213 Jewish women with ovarian cancer at 11 medical centers in North America and Israel and offered these women genetic testing for the three founder mutations. To establish the presence of nonfounder mutations in this population, we also completed the protein-truncation test on exon 11 of BRCA1 and exons 10 and 11 of BRCA2. We obtained a detailed family history on all women we studied who had cancer and on a control population of 386 Ashkenazi Jewish women without ovarian or breast cancer. A founder mutation was present in 41.3% of the women we studied. The cumulative incidence of ovarian cancer to age 75 years was found to be 6.3% for female first-degree relatives of the patients with ovarian cancer, compared with 2.0% for the female relatives of healthy controls (relative risk 3.2; 95% CI 1.5-6.8; P=.002). The relative risk to age 75 years for breast cancer among the female first-degree relatives was 2.0 (95% CI 1.4-3.0; P=.0001). Only one nonfounder mutation was identified (in this instance, in a woman of mixed ancestry), and the three founding mutations accounted for most of the observed excess risk of ovarian and breast cancer in relatives.     

<Emphasis Type="Italic">BRCA1</Emphasis> and <Emphasis Type="Italic">BRCA2</Emphasis> germline mutation analysis among Indian women from south India: identification of four novel mutations and high-frequency occurrence of 185delAG mutation

Mutations in the BRCA1 and BRCA2 genes profoundly increase the risk of developing breast and/or ovarian cancer among women. To explore the contribution of BRCA1 and BRCA2 mutations in the development of hereditary breast cancer among Indian women, we carried out mutation analysis of the BRCA1 and BRCA2 genes in 61 breast or ovarian cancer patients from south India with a positive family history of breast and/or ovarian cancer. Mutation analysis was carried out using conformation-sensitive gel electrophoresis (CSGE) followed by sequencing. Mutations were identified in 17 patients (28.0%); 15 (24.6%) had BRCA1 mutations and two (3.28%) had BRCA2 mutations. While no specific association between BRCA1 or BRCA2 mutations with cancer type was seen, mutations were more often seen in families with ovarian cancer. While 40% (4/10) and 30.8% (4/12) of families with ovarian or breast and ovarian cancer had mutations, only 23.1% (9/39) of families with breast cancer carried mutations in the BRCA1 and BRCA2 genes. In addition, while BRCA1 mutations were found in all age groups, BRCA2 mutations were found only in the age group of ≤40 years. Of the BRCA1 mutations, there were three novel mutations (295delCA; 4213T→A; 5267T→G) and three mutations that have been reported earlier. Interestingly, 185delAG, a BRCA1 mutation which occurs at a very high frequency in Ashkenazi Jews, was found at a frequency of 16.4% (10/61). There was one novel mutation (4866insT) and one reported mutation in BRCA2. Thus, our study emphasizes the importance of mutation screening in familial breast and/or ovarian cancers, and the potential implications of these findings in genetic counselling and preventive therapy.     

The founder mutations 185delAG and 5382insC in BRCA1 and 6174delT in BRCA2 appear in 60% of ovarian cancer and 30% of early-onset breast cancer patients among Ashkenazi women.

The mutations 185delAG, 188del11, and 5382insC in the BRCA1 gene and 6174delT in the BRCA2 gene were analyzed in 199 Ashkenazi and 44 non-Ashkenazi Jewish unrelated patients with breast and/or ovarian cancer. Of the Jewish Ashkenazi women with ovarian cancer, 62% (13/21) had one of the target mutations, as did 30% (13/43) of women with breast cancer alone diagnosed before the age 40 years and 10% (15/141) of those with breast cancer diagnosed after the age 40 years. Age at ovarian cancer diagnosis was not associated with carrier status. Of 99 Ashkenazi patients with no family history of breast and/or ovarian cancer, 10% carried one of the mutations; in two of them the mutation was proved to be paternally transmitted. One non-Ashkenazi Jewish ovarian cancer patient from Iraq carried the 185delAG mutation. Individual mutation frequencies among breast cancer Ashkenazi patients were 6.7% for 185delAG, 2.2% for 5382insC, and 4.5% for 6174delT, among ovarian cancer patients; 185delAG and 6174delT were about equally common (33% and 29%, respectively), but no ovarian cancer patient carried the 5382insC. More mutations responsible for inherited breast and ovarian cancer probably remain to be found in this population, since 79% of high-incidence breast cancer families and 35% of high-incidence breast/ovarian cancer families had none of the three known founder mutations.     

The predictive value of BRCA1 and BRCA2 mutation testing

Genetic testing for mutations in BRCA1 and BRCA2, two genes predisposing to breast and ovarian cancers, is available to women with a relevant family history. The aim of this study was to estimate the positive and negative predictive value of clinical sequence analysis of these genes. A reference graph showing positive and negative predictive values over a range of pre-test risk was derived, taking into account the sensitivity and specificity of a full-sequence analysis test. High positive and negative predictive values were found for women with pre-test risk between 4% and 40%, a range of risk commonly seen in clinical testing. The predictive value of full sequence and single-site analysis of BRCA1 and BRCA2, therefore, compares favorably with other diagnostic medical tests. Our results provide a numerical estimate of the predictive value of BRCA testing, and as such, provide a valuable tool to healthcare providers and families as they interpret BRCA1 and BRCA2 test results.     

Haplotype structure in Ashkenazi Jewish BRCA1 and BRCA2 mutation carriers

Three founder mutations in BRCA1 and BRCA2 contribute to the risk of hereditary breast and ovarian cancer in Ashkenazi Jews (AJ). They are observed at increased frequency in the AJ compared to other BRCA mutations in Caucasian non-Jews (CNJ). Several authors have proposed that elevated allele frequencies in the surrounding genomic regions reflect adaptive or balancing selection. Such proposals predict long-range linkage disequilibrium (LD) resulting from a selective sweep, although genetic drift in a founder population may also act to create long-distance LD. To date, few studies have used the tools of statistical genomics to examine the likelihood of long-range LD at a deleterious locus in a population that faced a genetic bottleneck. We studied the genotypes of hundreds of women from a large international consortium of BRCA1 and BRCA2 mutation carriers and found that AJ women exhibited long-range haplotypes compared to CNJ women. More than 50% of the AJ chromosomes with the BRCA1 185delAG mutation share an identical 2.1?Mb haplotype and nearly 16% of AJ chromosomes carrying the BRCA2 6174delT mutation share a 1.4?Mb haplotype. Simulations based on the best inference of Ashkenazi population demography indicate that long-range haplotypes are expected in the context of a genome-wide survey. Our results are consistent with the hypothesis that a local bottleneck effect from population size constriction events could by chance have resulted in the large haplotype blocks observed at high frequency in the BRCA1 and BRCA2 regions of Ashkenazi Jews.     

A comparison of BRCA1 mutation analysis by direct sequencing, SSCP and DHPLC

The most sensitive screening technique for genes that predispose patients for particular cancers is direct sequencing. However, sequencing of complex genes is technically demanding, costly and time-consuming. We have tested alternate screening techniques to find a fast sensitive method for detecting alterations of DNA in the large BRCA1 gene prior to sequencing. Sequencing of this gene is particularly arduous because it lacks clearly defined mutation sites. The single-strand conformation polymorphism (SSCP) technique is one of the most frequently used pre-screening methods but its sensitivity and efficiency is not completely satisfying. We have compared the SSCP assay with a newly developed technique called denaturing high performance liquid chromatography (DHPLC) to screen the BRCA1gene. We studied 23 patients at high risk for early onset breast and ovarian cancer and four controls. In these patients, a total of 113 fragments with sequence variations in the BRCA1 gene could be identified. The DHPLC technique resolved 100% of the DNA alterations that were observed in cycle sequencing. In contrast, mutation analysis by SSCP accounted for 94% of the detected variations. In addition, DHPLC screening allowed us to discriminate between different alterations in a single fragment, because of the characteristic elution profiles of the DNA molecules. Polymorphisms that were present in our samples could be predicted by means of DHPLC testing independently of sequence analysis. We conclude that DHPLC is a highly potent screening method for genetic analyses. It is highly sensitive, efficient and economical and can be automated. Electronic Publication     

Estimation of the RNU2 macrosatellite mutation rate by BRCA1 mutation tracing

Large tandem repeat sequences have been poorly investigated as severe technical limitations and their frequent absence from the genome reference hinder their analysis. Extensive allelotyping of this class of variation has not been possible until now and their mutational dynamics are still poorly known. In order to estimate the mutation rate of a macrosatellite, we analysed in detail the RNU2 locus, which displays at least 50 different alleles containing 5-82 copies of a 6.1 kb repeat unit. Mining data from the 1000 Genomes Project allowed us to precisely estimate copy numbers of the RNU2 repeat unit using read depth of coverage. This further revealed significantly different mean values in various recent modern human populations, favoring a scenario of fast evolution of this locus. Its proximity to a disease gene with numerous founder mutations, BRCA1, within the same linkage disequilibrium block, offered the unique opportunity to trace RNU2 arrays over a large timescale. Analysis of the transmission of RNU2 arrays associated with one ‘private’ mutation in an extended kindred and four founder mutations in multiple kindreds gave an estimation by maximum likelihood of 5 × 10⁻³ mutations per generation, which is close to that of microsatellites.