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Age-dependent penetrance of different germline mutations in the BRCA1 gene.

ABSTRACT: AIMS: BRCA1 gene mutations have been extensively studied in relation to breast and ovarian cancer susceptibility. Various genotype-phenotype correlation attempts have yielded important data pertaining to the consequences of BRCA1 mutations. However, little is known about the effects of recurrent BRCA mutations on expressivity and the age of onset of cancer in a population. This study addresses whether different exon mutations have variable expressivity especially in relation to the age of onset of breast cancer. METHODS: Using a step-wise systematic approach, culminating in the sequencing of all BRCA1 and BRCA2 exons with the addition of multiplex ligation-dependent probe amplification, the relationship between disease phenotypes and gene mutations in 219 individuals and their family members was examined. RESULTS: It is shown that different BRCA1 gene mutations have distinct effects that influence the age of onset of breast or ovarian cancer. Mutations in exon 2 of the BRCA1 gene had significantly lower penetrance compared with mutations of exons 11, 13 and 20. The median age of affliction with breast cancer was 55 years for 185delAG in exon 2 (95% confidence interval (CI) 46.7 to 59.5), 47 years for the 4184delTCAA mutation in exon 11 (95% CI 39 to 55.4), and 41 years for exon 13 duplication (95% CI 32.9 to 49.7) of the BRCA1 gene. Moreover, 14 novel mutations in BRCA1 and BRCA2 genes in the Yorkshire/Humberside population were identified. CONCLUSIONS: The 185delAG mutation of the BRCA1 gene is a low penetrance mutation that is age dependent especially when compared with the exon 13 duplication mutation. The data have important ramifications on screening, genetic counselling and prophylactic treatment of BRCA1 gene mutation carriers.

SUBMITTER: Al-Mulla F

PROVIDER: S-EPMC2656651 | biostudies-literature | 2009 Apr

REPOSITORIES: biostudies-literature

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Age-dependent penetrance of different germline mutations in the BRCA1 gene.

Al-Mulla F F Bland J M JM Serratt D D Miller J J Chu C C Taylor G T GT

Journal of clinical pathology 20090401 4

<h4>Aims</h4>BRCA1 gene mutations have been extensively studied in relation to breast and ovarian cancer susceptibility. Various genotype-phenotype correlation attempts have yielded important data pertaining to the consequences of BRCA1 mutations. However, little is known about the effects of recurrent BRCA mutations on expressivity and the age of onset of cancer in a population. This study addresses whether different exon mutations have variable expressivity especially in relation to the age of ...[more]

PMID: 19329713

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Project description: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.

Dataset Information

Age-dependent penetrance of different germline mutations in the BRCA1 gene.

Publications

Age-dependent penetrance of different germline mutations in the BRCA1 gene.

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