Haplotype and phenotype analysis of nine recurrent BRCA2 mutations in 111 families: results of an international study.

Several BRCA2 mutations are found to occur in geographically diverse breast and ovarian cancer families. To investigate both mutation origin and mutation-specific phenotypes due to BRCA2, we constructed a haplotype of 10 polymorphic short tandem-repeat (STR) markers flanking the BRCA2 locus, in a set of 111 breast or breast/ovarian cancer families selected for having one of nine recurrent BRCA2 mutations. Six of the individual mutations are estimated to have arisen 400-2,000 years ago. In particular, the 6174delT mutation, found in approximately 1% of individuals of Ashkenazi Jewish ancestry, was estimated to have arisen 29 generations ago (1-LOD support interval 22-38). This is substantially more recent than the estimated age of the BRCA1 185delAG mutation (46 generations), derived from our analogous study of BRCA1 mutations. In general, there was no evidence of multiple origins of identical BRCA2 mutations. Our study data were consistent with the previous report of a higher incidence of ovarian cancer in families with mutations in a 3.3-kb region of exon 11 (the ovarian cancer cluster region [OCCR]) (P=.10); but that higher incidence was not statistically significant. There was significant evidence that age at diagnosis of breast cancer varied by mutation (P<.001), although only 8% of the variance in age at diagnosis could be explained by the specific mutation, and there was no evidence of family-specific effects. When the age at diagnosis of the breast cancer cases was examined by OCCR, cases associated with mutations in the OCCR had a significantly older mean age at diagnosis than was seen in those outside this region (48 years vs. 42 years; P=.0005).     

Screening for genomic rearrangements in families with breast and ovarian cancer identifies BRCA1 mutations previously missed by conformation-sensitive gel electrophoresis or sequencing

The frequency of genomic rearrangements in BRCA1 was assessed in 42 American families with breast and ovarian cancer who were seeking genetic testing and who were subsequently found to be negative for BRCA1 and BRCA2 coding-region mutations. An affected individual from each family was tested by PCR for the exon 13 duplication (Puget et al. 1999a) and by Southern blot analysis for novel genomic rearrangements. The exon 13 duplication was detected in one family, and four families had other genomic rearrangements. A total of 5 (11. 9%) of the 42 families with breast/ovarian cancer who did not have BRCA1 and BRCA2 coding-region mutations had mutations in BRCA1 that were missed by conformation-sensitive gel electrophoresis or sequencing. Four of five families with BRCA1 genomic rearrangements included at least one individual with both breast and ovarian cancer; therefore, 4 (30.8%) of 13 families with a case of multiple primary breast and ovarian cancer had a genomic rearrangement in BRCA1. Families with genomic rearrangements had prior probabilities of having a BRCA1 mutation, ranging from 33% to 97% (mean 70%) (Couch et al. 1997). In contrast, in families without rearrangements, prior probabilities of having a BRCA1 mutation ranged from 7% to 92% (mean 37%). Thus, the prior probability of detecting a BRCA1 mutation may be a useful predictor when considering the use of Southern blot analysis for families with breast/ovarian cancer who do not have detectable coding-region mutations.     

Prevalence of<Emphasis Type="Italic"> BRCA1</Emphasis> and<Emphasis Type="Italic"> BRCA2</Emphasis> mutations among clinic-based African American families with breast cancer

To define the prevalence and relative contributions of BRCA1 and BRCA2 mutations among African American families with breast cancer, we analyzed 28 DNA samples from patients identified through two oncology clinics. The entire coding regions of BRCA1 and BRCA2 were screened by protein truncation test, heteroduplex analysis, or single-stranded conformation polymorphism followed by DNA sequencing of variant bands. Deleterious protein-truncating BRCA1 and BRCA2 mutations were identified in five patients or 18% of the entire cohort. Only 8% (1 of 13) of women with a family history of breast cancer, but no ovarian cancer, had mutations. The mutation rates were higher for women from families with a history of breast cancer and at least one ovarian cancer (three of six, 50%). One woman with a family history of undocumented cancers was also found to carry a deleterious mutation in BRCA2. The spectrum of mutations was unique in that one novel BRCA1 mutation (1625del5) and three novel BRCA2 mutations (1536del4, 6696delTC, and 7795delCT) were identified. No recurrent mutations were identified in this cohort, although one BRCA2 (2816insA) mutation had been previously reported. In addition, two BRCA1 and four BRCA2 missense mutations of unknown significance were identified, one of which was novel. Taken together with our previous report on recurrent mutations seen in unrelated families, we conclude that African Americans have a unique mutation spectrum in BRCA1 and BRCA2 genes, but recurrent mutations are likely to be more widely dispersed and therefore not readily identifiable in this population.     

A high proportion of novel mutations in BRCA1 with strong founder effects among Dutch and Belgian hereditary breast and ovarian cancer families

We have identified 79 mutations in BRCA1 in a set of 643 Dutch and 23 Belgian hereditary breast and ovarian cancer families collected either for research or for clinical diagnostic purposes. Twenty-eight distinct mutations have been observed, 18 of them not previously reported and 12 of them occurring more than once. Most conspicuously, a 2804delAA mutation has been found 19 times and has never been reported outside the Netherlands. A common haplotype spanning ≥375 kb could be identified for each of the nine examined recurrent mutations, indicating the presence of multiple BRCA1 founder mutations in the Dutch population. The 2804delAA mutation has been estimated to have originated ~32 generations ago. No specific breast or ovarian cancer phenotype could be assigned to any of the common mutations, and the ovarian cancer incidence among 18 families with the 2804delAA mutation was heterogeneous.     

Founder mutations in the BRCA1 gene in Polish families with breast-ovarian cancer

We have undertaken a hospital-based study, to identify possible BRCA1 and BRCA2 founder mutations in the Polish population. The study group consisted of 66 Polish families with cancer who have at least three related females affected with breast or ovarian cancer and who had cancer diagnosed, in at least one of the three affected females, at age <50 years. A total of 26 families had both breast and ovarian cancers, 4 families had ovarian cancers only, and 36 families had breast cancers only. Genomic DNA was prepared from the peripheral blood leukocytes of at least one affected woman from each family. The entire coding region of BRCA1 and BRCA2 was screened for the presence of germline mutations, by use of SSCP followed by direct sequencing of observed variants. Mutations were found in 35 (53%) of the 66 families studied. All but one of the mutations were detected within the BRCA1 gene. BRCA1 abnormalities were identified in all four families with ovarian cancer only, in 67% of 27 families with both breast and ovarian cancer, and in 34% of 35 families with breast cancer only. The single family with a BRCA2 mutation had the breast-ovarian cancer syndrome. Seven distinct mutations were identified; five of these occurred in two or more families. In total, recurrent mutations were found in 33 (94%) of the 35 families with detected mutations. Three BRCA1 abnormalities-5382insC, C61G, and 4153delA-accounted for 51%, 20%, and 11% of the identified mutations, respectively.     

Founder BRCA1 and BRCA2 mutations in Ashkenazi Jews in Israel: frequency and differential penetrance in ovarian cancer and in breast-ovarian cancer families.

Germ-line BRCA1 and BRCA2 mutations account for most of familial breast-ovarian cancer. In Ashkenazi Jews, there is a high population frequency (approximately 2%) of three founder mutations: BRCA1 185delAG, BRCA1 5382insC, and BRCA2 6174delT. This study examined the frequency of these mutations in a series of Ashkenazi women with ovarian cancer unselected for family history, compared with the frequency of these mutations in families ascertained on the basis of family history of at least two affected women. Penetrance was compared, both according to the method of family ascertainment (i.e., on the basis of an unselected ovarian cancer proband vs. on the basis of family history) and for the BRCA1 founder mutations compared with the BRCA2 6174delT mutation. There was a high frequency (10/22; [45%]) of germ-line mutations in Ashkenazi women with ovarian cancer, even in those with minimal or no family history (7/18 [39%]). In high-risk Ashkenazi families, a founder mutation was found in 59% (25/42). Families with any case of ovarian cancer were significantly more likely to segregate a founder mutation than were families with site-specific breast cancer. Penetrance was higher in families ascertained on the basis of family history than in families ascertained on the basis of an unselected proband, but this difference was not significant. Penetrance of BRCA1 185delAG and BRCA1 5382insC was significantly higher than penetrance of BRCA2 6174delT (hazard ratio 2.1 [95% CI 1.2-3.8]; two-tailed P = .01). Thus, the high rate of germ-line BRCA1/BRCA2 mutations in Ashkenazi women and families with ovarian cancer is coupled with penetrance that is lower than previously estimated. This has been shown specifically for the BRCA2 6174delT mutation, but, because of ascertainment bias, it also may be true for BRCA1 mutations.     

Prevalence and contribution of BRCA1 mutations in breast cancer and ovarian cancer: results from three U.S. population-based case-control studies of ovarian cancer.

We investigate the familial risks of cancers of the breast and ovary, using data pooled from three population-based case-control studies of ovarian cancer that were conducted in the United States. We base estimates of the frequency of mutations of BRCA1 (and possibly other genes) on the reported occurrence of breast cancer and ovarian cancer in the mothers and sisters of 922 women with incident ovarian cancer (cases) and in 922 women with no history of ovarian cancer (controls). Segregation analysis and goodness-of-fit testing of genetic models suggest that rare mutations (frequency .0014; 95% confidence interval .0002-.011) account for all the observed aggregation of breast cancer and ovarian cancer in these families. The estimated risk of breast cancer by age 80 years is 73.5% in mutation carriers and 6.8% in noncarriers. The corresponding estimates for ovarian cancer are 27.8% in carriers and 1.8% in noncarriers. For cancer risk in carriers, these estimates are lower than those obtained from families selected for high cancer prevalence. The estimated proportion of all U.S. cancer diagnoses, by age 80 years, that are due to germ-line BRCA1 mutations is 3.0% for breast cancer and 4.4% for ovarian cancer. Aggregation of breast cancer and ovarian cancer was less evident in the families of 169 cases with borderline ovarian cancers than in the families of cases with invasive cancers. Familial aggregation did not differ by the ethnicity of the probands, although the number of non-White and Hispanic cases (N = 99) was sparse.     

Founder BRCA1 and BRCA2 mutations in French Canadian breast and ovarian cancer families.

We have identified four mutations in each of the breast cancer-susceptibility genes, BRCA1 and BRCA2, in French Canadian breast cancer and breast/ovarian cancer families from Quebec. To identify founder effects, we examined independently ascertained French Canadian cancer families for the distribution of these eight mutations. Mutations were found in 41 of 97 families. Six of eight mutations were observed at least twice. The BRCA1 C4446T mutation was the most common mutation found, followed by the BRCA2 8765delAG mutation. Together, these mutations were found in 28 of 41 families identified to have a mutation. The odds of detection of any of the four BRCA1 mutations was 18.7x greater if one or more cases of ovarian cancer were also present in the family. The odds of detection of any of the four BRCA2 mutations was 5.3x greater if there were at least five cases of breast cancer in the family. Interestingly, the presence of a breast cancer case <36 years of age was strongly predictive of the presence of any of the eight mutations screened. Carriers of the same mutation, from different families, shared similar haplotypes, indicating that the mutant alleles were likely to be identical by descent for a mutation in the founder population. The identification of common BRCA1 and BRCA2 mutations will facilitate carrier detection in French Canadian breast cancer and breast/ovarian cancer families.     

Prevalence and penetrance of germline BRCA1 and BRCA2 mutations in a population series of 649 women with ovarian cancer

A population-based series of 649 unselected incident cases of ovarian cancer diagnosed in Ontario, Canada, during 1995-96 was screened for germline mutations in BRCA1 and BRCA2. We specifically tested for 11 of the most commonly reported mutations in the two genes. Then, cases were assessed with the protein-truncation test (PTT) for exon 11 of BRCA1, with denaturing gradient gel electrophoresis for the remainder of BRCA1, and with PTT for exons 10 and 11 of BRCA2. No mutations were found in all 134 women with tumors of borderline histology. Among the 515 women with invasive cancers, we identified 60 mutations, 39 in BRCA1 and 21 in BRCA2. The total mutation frequency among women with invasive cancers, 11.7% (95% confidence interval [95%CI] 9.2%-14.8%), is higher than previous estimates. Hereditary ovarian cancers diagnosed at age <50 years were mostly (83%) due to BRCA1, whereas the majority (60%) of those diagnosed at age >60 years were due to BRCA2. Mutations were found in 19% of women reporting first-degree relatives with breast or ovarian cancer and in 6.5% of women with no affected first-degree relatives. Risks of ovarian, breast, and stomach cancers and leukemias/lymphomas were increased nine-, five-, six- and threefold, respectively, among first-degree relatives of cases carrying BRCA1 mutations, compared with relatives of noncarriers, and risk of colorectal cancer was increased threefold for relatives of cases carrying BRCA2 mutations. For carriers of BRCA1 mutations, the estimated penetrance by age 80 years was 36% for ovarian cancer and 68% for breast cancer. In breast-cancer risk for first-degree relatives, there was a strong trend according to mutation location along the coding sequence of BRCA1, with little evidence of increased risk for mutations in the 5' fifth, but 8.8-fold increased risk for mutations in the 3' fifth (95%CI 3.6-22.0), corresponding to a carrier penetrance of essentially 100%. Ovarian, colorectal, stomach, pancreatic, and prostate cancer occurred among first-degree relatives of carriers of BRCA2 mutations only when mutations were in the ovarian cancer-cluster region (OCCR) of exon 11, whereas an excess of breast cancer was seen when mutations were outside the OCCR. For cancers of all sites combined, the estimated penetrance of BRCA2 mutations was greater for males than for females, 53% versus 38%. Past studies may have underestimated the contribution of BRCA2 to ovarian cancer, because mutations in this gene cause predominantly late-onset cancer, and previous work has focused more on early-onset disease. If confirmed in future studies, the trend in breast-cancer penetrance, according to mutation location along the BRCA1 coding sequence, may have significant impact on treatment decisions for carriers of BRCA1-mutations. As well, BRCA2 mutations may prove to be a greater cause of cancer in male carriers than previously has been thought.     

Offspring gender ratio and the rate of recurrent spontaneous miscarriages in jewish women at high risk for breast/ovarian cancer

BRCA1/BRCA2 germline mutations are associated with an increased breast/ovarian cancer risk. Offspring gender ratios may be skewed against male births in BRCA1 mutation carriers. In addition, the lack of viable homozygous BRCA1/BRCA2-mutation carriers implies that recurrent miscarriages may be associated with homozygous fetuses. Jewish Israeli high-risk women who were tested for being carriers of the predominant BRCA1/BRCA2 mutations in Jewish high-risk families were analyzed for the sex of offspring and the rate of spontaneous miscarriages. Overall, 817 women participated: 393 BRCA1/BRCA2-mutation carriers (229 with breast/ovarian cancer) and 424 high-risk noncarriers (208 with breast/ovarian cancer). No differences between the male-to-female offspring ratios of all study groups were noted. Among mutation carriers, the offspring male-to-female ratio was 0.97 (444 : 460), and among mutation carriers with cancer it was 0.92 (262 : 284). Similarly, no offspring gender skewing was noted among high-risk noncarriers, regardless of health status. The rates of three or more spontaneous miscarriages among participants with at least one live birth were 4.37% (15/343) among mutation carriers and 3% (12/401) among high-risk women (P = not significant). In conclusion, the offspring gender ratio is similar in high-risk Jewish families and in the general population. The issue of the rate of recurrent miscarriages in high-risk Jewish women is unresolved.     

A low proportion of BRCA2 mutations in Finnish breast cancer families.

One hundred breast cancer families were identified at the Helsinki University Central Hospital in Finland and were screened for germ-line mutations in the coding regions and splice boundaries of the BRCA2 gene. Eight families (8%) were found to carry five different mutations, all of which are predicted to prematurely truncate the protein product. These BRCA2 families have early-onset breast cancer (mean and median age = 49 years), with four of the eight families including ovarian cancer but with no families including male breast cancer. A wide spectrum of other cancers also is seen in these families. Three mutations were identified in more than one family, and haplotype analysis in the families suggested a common founder for each recurrent mutation. One recurrent mutation, 999del5, previously has been noted as a common mutation in Iceland. The relationship between the Icelandic 999del5 mutation and the Finnish 999del5 mutation was explored by comparison of families from both countries. A common haplotype covering a minimal region intragenic to the BRCA2 gene was shared between the Icelandic and the Finnish mutation carriers.     

Founding BRCA1 mutations in hereditary breast and ovarian cancer in southern Sweden.

Nine different germ-line mutations in the BRCA1 breast and ovarian cancer susceptibility gene were identified in 15 of 47 kindreds from southern Sweden, by use of SSCP and heteroduplex analysis of all exons and flanking intron region and by a protein-truncation test for exon 11, followed by direct sequencing. All but one of the mutations are predicted to give rise to premature translation termination and include seven frameshift insertions or deletions, a nonsense mutation, and a splice acceptor site mutation. The remaining mutation is a missense mutation (Cys61Gly) in the zinc-binding motif. Four novel Swedish founding mutations were identified: the nucleotide 2595 deletion A was found in five families, the C 1806 T nonsense mutation in three families, the 3166 insertion TGAGA in three families, and the nucleotide 1201 deletion 11 in two families. Analysis of the intragenic polymorphism D17S855 supports common origins of the mutations. Eleven of the 15 kindreds manifesting BRCA1 mutations were breast-ovarian cancer families, several of them with a predominant ovarian cancer phenotype. The set of 32 families in which no BRCA1 alterations were detected included 1 breast-ovarian cancer kindred manifesting clear linkage to the BRCA1 region and loss of the wild-type chromosome in associated tumors. Other tumor types found in BRCA1 mutation/haplotype carriers included prostatic, pancreas, skin, and lung cancer, a malignant melanoma, an oligodendroglioma, and a carcinosarcoma. In all, 12 of 16 kindreds manifesting BRCA1 mutation or linkage contained ovarian cancer, as compared with only 6 of the remaining 31 families (P<.001). The present study confirms the involvement of BRCA1 in disease predisposition for a subset of hereditary breast cancer families often characterized by ovarian cancers.     

<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.     

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.     

Penetrances of BRCA1 1675delA and 1135insA with respect to breast cancer and ovarian cancer.

For genetic counseling and predictive testing in families with inherited breast-ovarian cancer, penetrances and expressions of the underlying mutations should be known. We have previously reported two BRCA1 founder mutations in the Norwegian population. Index cases for the present study were found two different ways: through a series of consecutive ovarian cancers (n=16) and through our family cancer clinic (n=14). Altogether, 20 of the patients had BRCA1 1675delA, and 10 had 1135insA. Their relatives were described with respect to absence/presence of breast and/or ovarian cancer. Of 133 living female relatives, 83 (62%) were tested for the presence of a mutation. No difference, in penetrance and expression, between the two mutations were found, whereas differences according to method of ascertainment were seen. The overall findings were that disease started to occur at age 30 years and that by age 50 years 48% of the mutation-carrying women had experienced breast and/or ovarian cancer. More ovarian cancers than breast cancers were recorded. Both penetrance and expression (breast cancer vs. ovarian cancer) were different from those in reports of the Ashkenazi founder mutations. Whether the reported differences reflect true differences and/or methodological problems is discussed. An observed excess of mutation carriers could not be accounted for by methodological problems; possible explanations were a "true" low penetrance or preferential segregation.     

Detection of eight BRCA1 mutations in 10 breast/ovarian cancer families, including 1 family with male breast cancer.

Genetic epidemiological evidence suggests that mutations in BRCA1 may be responsible for approximately one half of early onset familial breast cancer and the majority of familial breast/ovarian cancer. The recent cloning of BRCA1 allows for the direct detection of mutations, but the feasibility of presymptomatic screening for cancer susceptibility is unknown. We analyzed genomic DNA from one affected individual from each of 24 families with at least three cases of ovarian or breast cancer, using SSCP assays. Variant SSCP bands were subcloned and sequenced. Allele-specific oligonucleotide hybridization was used to verify sequence changes and to screen DNA from control individuals. Six frameshift and two missense mutations were detected in 10 different families. A frameshift mutation was detected in a male proband affected with both breast and prostate cancer. A 40-bp deletion was detected in a patient who developed intra-abdominal carcinomatosis 1 year after prophylactic oophorectomy. Mutations were detected throughout the gene, and only one was detected in more than a single family. These results provide further evidence that inherited breast and ovarian cancer can occur as a consequence of a wide array of BRCA1 mutations. These results suggests that development of a screening test for BRCA1 mutations will be technically challenging. The finding of a mutation in a family with male breast cancer, not previously thought to be related to BRCA1, also illustrates the potential difficulties of genetic counseling for individuals known to carry mutations.     

Frequent occurrence of BRCA2 linkage in Icelandic breast cancer families and segregation of a common BRCA2 haplotype.

Cloning of a breast cancer-predisposing gene (BRCA2) on chromosome 13Q12-14 has been reported recently. We analyzed seven large Icelandic breast cancer families with markers from the BRCA2 region. Five families showed strong evidence of linkage. The maximum two-point LOD scores for the five BRCA2-linked families ranged from 1.06 to 3.19. Haplotype analyses revealed a region with identical allele sizes between the families, suggesting that they have inherited the mutation from a common ancestor. Cancer types other than breast cancer occur in individuals, segregating the affected haplotype within these families. This suggests that mutations in the gene may also confer some risk of other malignancies in both males and females.     

A high proportion of mutations in the BRCA1 gene in German breast/ovarian cancer families with clustering of mutations in the 3′ third of the gene

We have analyzed 61 German breast and breast/ovarian cancer families for BRCA1 mutations using single-strand conformation polymorphism analysis (SSCP) followed by sequencing. Forty-seven of the families had at least three cases (at least two under 60 years) and 14 families had only two cases of breast/ovarian cancer (at least one under 50 years). Twenty-eight families were breast/ovarian and 33 were breast cancer-only families. Eighteen mutations in BRCA1 were detected in 11/28 breast/ovarian cancer families and 7/33 breast cancer families and none in the families with only two cases. We identified 17 truncation mutations (8 frameshift, 7 nonsense and 2 splice variants) and one missense mutation. Seven of these are novel and two, the 5382insC and 5622C→T mutations, occurred in two apparently unrelated families. The genotype of the two families with the 5382insC mutation is compatible with the rare haplotype segregating with the 5382insC mutation in different populations, further supporting its European origin. One unclassified missense alteration, R841W, was found in one family but did not segregate with the disease, suggesting that it is more likely a polymorphism. We also report and discuss the sequence of several new unclassified single-nucleotide changes first identified by SSCP. Of the 18 mutations, 13 occurred in the 3′ third of the gene (end of exon 11–24) and ovarian cancers were found in eight of these families. Received: 5 February 1998 / Accepted: 7 April 1998     

Two distinct origins of a common BRCA1 mutation in breast-ovarian cancer families: a genetic study of 15 185delAG-mutation kindreds.

We screened 163 women from breast-ovarian cancer-prone families, as well as 178 individuals affected with breast and/or ovarian cancer but unselected for family history, for germ-line mutations in exon 2 of BRCA1, by SSCP analysis and direct sequencing. A total of 25 mutations were detected. Thirteen of 64 Jewish Ashkenazi women and 2 non-Jewish individuals were found to possess the 185delAG mutation. Haplotype data for all 15 individuals, with markers intragenic to BRCA1, suggest that the Jewish Ashkenazi individuals share a common ancestry that is distinct from the lineage shared by the other two women. These data provide the first evidence of two distinct lines of transmission for the 185delAG mutation, only one of which has its origins in the Jewish Ashkenazi population. Our screening also uncovered 10 affected individuals with an 11-bp deletion at nucleotide 188 of BRCA1 (188del11), 4 of whom are Ashkenazi Jews. This is only the third reported mutation detected within the Jewish Ashkenazi population and may represent the second most common alteration in BRCA1 found in Ashkenazi Jews in the United States. The observed overrepresentation of specific mutations within a subgroup of the general population may eventually contribute to the development of inexpensive and routine tests for BRCA1 mutations, as well as to the elucidation of other contributory factors (e.g., diet, environment, and chemical exposures) that may play a key role in cancer initiation and development. The implications of the mutational data, as well as the role that founder effect, demographic history, and penetrance play in the resulting observed phenomena, are discussed.