BRCAI and BRCA2 Mutation Analysis in At-risk African-American Families: Results and Implications

Abstract

The incidence of BRCA1 germ-line mutations in at-risk individuals is controversial. In Caucasians, the detection of BRCA1 mutations varies from 5-40%. Even more controversial is the incidence of BRCA1 mutations and genetic variants in at-risk African-Americans (AA), which has been reported as ranging from very low to incidences equaling those in Caucasians. We report our results of completed BRCA1 and BRCA2 analyses in 20 AA families at-risk for breast/ovarian cancer. Families were ascertained based on a history of breast cancer or breast/ovarian cancer and further subdivided into the following categories: high-risk (HR; three affected 1st degree relatives; 10 families), moderate-risk (MR, two affected 1st degree relatives, 7 families) and undetermined risk (UR; single affected with medical information being updated).

Germ-line alterations in BRCA1 and BRCA2 coding sequences were first detected using a series of exon-specific PCR primers in SSCP analysis to visualize regions of genetic variation. These experiments were followed by DNA sequencing of SSCP variants, using either DNA extracted and purified from SSCP variant bands, or the corresponding PCR product generated from genomic DNA. A limited number of BRCA1 polymorphic intronic variants detected as a result of these studies were analyzed for their effect on BRCA1 mRNA splicing using DNA and RNA extracted from patients' peripheral blood in a splicing assay developed by Myriad Genetics.

We have identified only one deleterious mutation (3875 del GTCT, BRCA1, a MR family), in either BRCA1 or BRCA2 in this patient cohort. However, a number of exonic and intronic polymorphic variants in BRCA2 have been detected, as well as two different AA-specific BRCA1 intronic polymorphisms detected in two HR unrelated families in which a disease-causing mutation was not otherwise detected. In addition, two missense mutations (one in BRCA1 and one in BRCA2) were detected in two unrelated families, again in the absence of anv apparent disuse-causing mutation. The novel BRCA1 missense mutation [exon 19 (W 1718C)] in the second HR family appears to co-segregate wilh breast cancer The relative frequencies of these BRCA1 and BRCA2 variants in Caucasian and AA control populations is being evaluated. In conclusion, our data support other recent reports concerning low germ-line BRCA1 and BRCA2 mutation rales in AA patients, and suggest a possible role for AA-specific BRCA1 and BRCA2 variants in modulating breast cancer risk.