Risks of cancer due to a single BRCA1 mutation in an extended Utah kindred.

Objective: Germline mutations in the BRCA1 gene are associated with an increased risk of breast and ovarian cancer, but there is controversy about the true magnitude of these risks. Observed differences can arise from several sources, both genetic and methodological. To examine the efficiency and bias associated with different methods of risk calculation, we analyzed a single mutation in a large pedigree with known ascertainment.