The Tyr978X BRCA1 Mutation in Non-Ashkenazi Jews: Occurrence in High-Risk Families, General Population and Unselected Ovarian Cancer Patients

Background: In Jewish individuals of Ashkenazi (East European) decent, three predominant mutations, 185 delAG and 5382insC (BRCA1) and 6174delT (BRCA2), seem to account for a substantial portion of germline mutations in high-risk breast/ovarian cancer families. Among non-Ashkenazi Jews, the 185delAG and the Tyr978X mutations, as well as several 'private' mutations have been reported within the BRCA1 gene. Objective: Assessing the occurrence rate of the Tyr978X BRCA1 germline mutation in Jewish non-Ashkenazi individuals: high-risk familial cases, unselected ovarian cancer patients and the general average risk Jewish Iraqi population. In addition, finding proof that this is a founder mutation. Methods: PCR amplification of the relevant fragment of the BRCA1 gene from constitutional DNA followed by restriction enzyme digest that differentiates the wild type from the mutant allele. In addition, BRCA1-linked markers were used for haplotype analysis. Results: The Tyr978X BRCA1 mutation was detected in 3/289 (1%) of the average-risk Jewish Iraqi population, in 7/408 (1.7%) high-risk Jewish non-Ashkenazi individuals (representing 332 unrelated families) and in 1/81 (1.2%) of unselected Jewish non-Ashkenazi ovarian cancer patients. Allelotyping using BRCA1-linked markers revealed an identical allelic pattern in all mutation carriers with the intragenic markers. Conclusions: Our findings suggest that this mutation is prevalent in Iraqi Jews, represents a founder mutation, and should be incorporated into the panel of mutations analyzed in high-risk families of the appropriate ethnic background. Copyright 2001 S. Karger AG, Basel

Immunohistochemical analyses of sporadic and familial (185delAG carriers) ovarian cancer in Israel

A single germ line mutation in BRCA1, (185delAG) is detected in a substantial portion of Jewish Israeli patients with ovarian cancer. Whether disease phenotypes differ in BRCA1 mutation carriers and sporadic cases is presently a subject for debate. To gain insight into this issue, we analysed tumours from 65 Jewish women with ovarian cancer, 29 (45%) were 185delAG BRCA1 mutation carriers, and 36 (55%) were non-carriers of any of the predominant Jewish mutations in BRCA1 or BRCA2 (sporadic). In 19/29 mutation carriers (66%) diagnosis was made prior to age 60 years, compared with 14/36 (39%) of the non-carriers (P=0.03; Yates corrected P=0.06). Low malignant potential ('borderline') tumours were detected less frequently among carriers (2/29; 7%) than non-carriers (9/36; 25%) (P=0.03; one tail P=0.05). Immunohistochemical analysis in invasive carcinoma (n=54) showed that 17/27 carriers (63%) and 18/27 non-carriers (67%) had positive nuclear staining with a p53 antibody. In 4/27 carriers (15%) and 3/25 non-carriers (12%), 25% or more of the tumour cells stained positive for Ki-67, an insignificant difference. Results were not altered by including borderline tumours (n=11) in these analyses. We conclude that the rate of TP53 inactivation and proliferative index in ovarian cancer, are similar for 185delAG BRCA1 mutation carriers and sporadic cases.

Significantly lower rates of BRCA1/BRCA2 founder mutations in Ashkenazi women with sporadic compared with familial early onset breast cancer

To delineate the clinical, genetic and family history attributes in Jewish Ashkenazi women with early onset (< 42 years) breast cancer we genotyped such women for the three predominant Jewish Ashkenazi mutations in BRCA1 (185delAG and 5382insC) and BRCA2 (6174delT). The study cohort was composed of 172 women diagnosed with breast cancer at or before the age of 42 years, obtained from the oncology department registry. Mutations were identified in 54 women (31%). Of 79 women with a positive family history for breast and/or ovarian cancer, and 93 with no such family history, 45 (57%) and 9 (10%), respectively, were mutation carriers (chi2 = 46; P < 0.001). Contralateral breast cancer occurred in 15 of 54 mutation carriers (28%) compared with 8 of 118 (7%) non-carriers (chi2= 14; P < 0.001). Early onset breast cancer per se is a weak predictor of finding germ line mutation(s) in BRCA1 and BRCA2, unless associated with a positive family history and/or bilaterality.

Rates of Jewish ancestral mutations in BRCA1 and BRCA2 in borderline ovarian tumors

BACKGROUND

Germline mutations in the BRCA1 and BRCA2 genes are known to be associated with an increased risk of breast and epithelial ovarian cancers. Two specific mutations, 185delAG-BRCA1 and 6174delT-BRCA2, have been detected in a substantial proportion (20%-60%) of unselected Ashkenazi Jewish patients--i.e., Jewish patients of Eastern/Northern European descent--with invasive ovarian cancer and in a measurable proportion (2%) of the general Ashkenazi Jewish population. However, uncertainty exists concerning the heritable basis of borderline ovarian tumors and whether these tumors represent an early form of ultimately invasive disease. To gain insight into these issues, we determined the rates of 185delAG-BRCA1 and 6174delT-BRCA2 mutations in patients with borderline ovarian tumors.

METHODS

Analysis of 185delAG-BRCA1 and 6174delT-BRCA2 germline mutations was performed by use of a heteroduplex formation assay in samples from 46 consecutive patients with borderline ovarian tumors and 59 consecutive patients with invasive epithelial ovarian cancers. Forty-eight samples were also analyzed by restriction enzyme analysis for the presence of the 5382insC-BRCA1 mutation, a mutation detected in 2.2% of Ashkenazi Jewish patients with breast, but not ovarian, cancer.

RESULTS

One (2.2%) of the 46 patient with borderline tumors was identified as a carrier of the 185delAG-BRCA1 mutation, and no patients were found to carry the 6174delT-BRCA2 mutation. Nineteen (32%) of the 59 patients with invasive ovarian cancer were found to carry one of these two mutations; 17 carried 185delAG-BRCA1 and two carried 6174delT-BRCA2 (chi2 test with continuity correction, P = .00028). None of the patients analyzed for 5382insC-BRCA1 were found to carry the mutation. In one high-risk family that included 185delAG-BRCA1 carriers, a single patient with stage IIIc borderline ovarian tumor did not carry the mutation.

CONCLUSIONS

Invasive epithelial and borderline ovarian tumors appear to differ in their genetic predisposition and in the molecular mechanisms underlying their genesis.

The 185delAG BRCA1 mutation originated before the dispersion of Jews in the diaspora and is not limited to Ashkenazim

The 185delAG mutation in BRCA1 is detected in Ashkenazi Jews both in familial breast and ovarian cancer and in the general population. All tested Ashkenazi mutation carriers share the same allelic pattern at the BRCA1 locus. Our previous study showed that this 'Ashkenazi' mutation also occurs in Iraqi Jews with a similar allelic pattern. We extended our analysis to other non-Ashkenazi subsets: 354 of Moroccan origin, 200 Yemenites and 150 Iranian Jews. Heteroduplex analysis complemented by direct DNA sequencing of abnormally migrating bands were employed. Four of Moroccan origin (1. 1%) and none of the Yemenites or Iranians was a carrier of the 185delAG mutation. BRCA1 allelic patterns were determined for four of these individuals and for 12 additional non-Ashkenazi 185delAG mutation carriers who had breast/ovarian cancer. Six non-Ashkenazi individuals shared the common 'Ashkenazi haplotype', four had a closely related pattern, and the rest ( n = 6) displayed a distinct BRCA1 allelic pattern. We conclude that the 185delAG BRCA1 mutation occurs in some non-Ashkenazi populations at rates comparable with that of Ashkenazim. The majority of Jewish 185delAG mutation carriers have a common allelic pattern, supporting the founder effect notion, but dating the mutation's origin to an earlier date than currently estimated. However, the different allelic pattern at the BRCA1 locus even in some Jewish mutation carriers, might suggest that the mutation arose independently.

[Experience at Sheba Hospital in oncogenetic counseling and genetic testing of women with a high risk for breast and ovarian cancer]

There is inherited predisposition to breast and ovarian cancer in 5-10% of all women with these diseases. Germline mutations in BRCA1 and BRCA2 presumably account for most of the genetically susceptible individuals. We summarize 2 years of experience in counseling and testing for inherited predisposition to these cancers. 597 women (from 320 families) have been evaluated since August 1995. 242 were evaluated for inherited predisposition to breast and ovarian cancer. One-third had clear-cut evidence of familial background. 74 families were of Ashkenazi origin; the age range of breast cancer was 30-35, of ovarian cancer 40-45. In 80% of families other cancers were also noted in first degree family members, including lung, colon, and prostate cancer and leukemia. Genetic testing revealed that 45% of affected and 25% of unaffected women were carriers of a mutation in BRCA1 or BRCA2: 67/90 185delAG (BRCA1), 12/90 6174delT (BRCA2), and 4/90 of 5382insC (BRCA1). In addition, a novel mutation in exon 11 of BRCA1 was detected, carried by 7/90 women. The experience gained in oncogenetic counseling and genetic testing for inherited cancer predisposition will eventually enable determining an optimal, rational therapeutic regimen in carriers of mutations.

Could the 185delAG BRCA1 mutation be an ancient Jewish mutation?

A predominant mutation within the BRCA1 predisposition gene, 185delAG, has been detected in about 1% of the Ashkenazi population, considered a high-risk group for breast and ovarian cancers. We examined 639 unrelated healthy Jews of Iraqi extraction, a presumed low-risk group, for the existence of this mutation. Three individuals were identified as 185delAG mutation carriers, and haplotype analysis of the Iraqi mutation carriers revealed that 2 of the Iraqis shared a common haplotype with 6 Ashkenazi mutation carriers, and 1 had a haplotype which differed by a single marker. This study suggests that the BRCA1 185delAG mutation also occurs in populations considered at low-risk for breast and ovarian cancers, and that it might have occurred prior to the dispersion of the Jewish people in the Diaspora, at least at the time of Christ.