[Show abstract][Hide abstract] ABSTRACT: Germ line inactivating mutations in BRCA1 confer susceptibility for breast and ovarian cancer. However, the relevance of the many missense changes in the gene for which the effect on protein function is unknown remains unclear. Determination of which variants are causally associated with cancer is important for assessment of individual risk. We used a functional assay that measures the transactivation activity of BRCA1 in combination with analysis of protein modeling based on the structure of BRCA1 BRCT domains. In addition, the information generated was interpreted in light of genetic data. We determined the predicted cancer association of 22 BRCA1 variants and verified that the common polymorphism S1613G has no effect on BRCA1 function, even when combined with other rare variants. We estimated the specificity and sensitivity of the assay, and by meta-analysis of 47 variants, we show that variants with <45% of wild-type activity can be classified as deleterious whereas variants with >50% can be classified as neutral. In conclusion, we did functional and structure-based analyses on a large series of BRCA1 missense variants and defined a tentative threshold activity for the classification missense variants. By interpreting the validated functional data in light of additional clinical and structural evidence, we conclude that it is possible to classify all missense variants in the BRCA1 COOH-terminal region. These results bring functional assays for BRCA1 closer to clinical applicability.
[Show abstract][Hide abstract] ABSTRACT: Recent evidence from our laboratory as well as others suggests that specific variants in BRCA1 and BRCA2 are associated with increased risk of breast cancer in women of African-American (AA) ancestry. Of particular note is the increasing number of missense mutations/unclassified variants in African-Americans, particularly in BRCA2. We are further investigating the association of these variants with disease risk in a cohort of 35 AA probands and their families. The current study is a two-part design: collection of prevalence data for all novel variants, and assessment of functional effects for selected BRCA1 mutations using a transcriptional assay. BRCA1 missense mutations were found in 14% (5/35) of the families, while 32% (13/35) of the probands had BRCA2 missense mutations. Several of the BRCA1 variants were novel, and we are currently studying their significance. We have determined that BRCA1 variant, W1718C, which was detected in one family segregating with breast cancer, exhibits a proven loss-of-function phenotype in transcriptional assays. Regarding BRCA2 missense mutations 5/13 (38%) missense mutations were novel, four of these were found in one family each, with two (E425E, V2820V) being the only variant detected. One variant, S2414S, was detected in two unrelated probands with breast cancer at less than 40 years of age. Prevalence data for 3 of the novel mutations (T77T, E425E, D1923A) are currently being collected. Thus far, for T777T and D1923A, each of these was not present in 80-100 AA control chromosomes. Evaluation of the biological effect of novel BRCA2 missense mutations awaits further development of a BRCA2 functional assay. Completion of this study should reveal important information regarding the association of BRCA1/BRCA2 missense mutations with breast and ovarian cancer risk in AA women.
Full-text · Article · Jul 2004 · Genetics in Medicine