BRCA1 in special populations.

A restricted number of mutant BRCA1 alleles are present at high frequency in the Ashkenazi Jewish population: 185delAG and 5382insC and, perhaps, 188del11. These mutations have provided a means to re-estimate the penetrance function of an abnormal BRCA1 allele to be in the range of 50-60% for breast cancer, and 8-16% for ovarian cancer. Moreover, there was an increased rate of prostate, but not colorectal, cancers in BRCA1 carriers. Further studies in the Ashkenazi population may provide one approach to identifying the environmental or genetic cofactors that modify the impact of an abnormal BRCA1 gene.