Novel inherited mutations and variable expressivity of BRCA1 alleles, including the founder mutation 185delAG in Ashkenazi Jewish families.

Thirty-seven families with four or more cases of breast cancer or breast and ovarian cancer were analyzed for mutations in BRCA1. Twelve different germ-line mutations, four novel and eight previously observed, were detected in 16 families. Five families of Ashkenazi Jewish descent carried the 185delAG mutation and shared the same haplotype at eight polymorphic markers spanning approximately 850 kb at BRCA1. Expressivity of 185delAG in these families varied, from early-onset breast cancer without ovarian cancer. Mutation 4184delTCAA occurred independently in two families. In one family, penetrance was complete, with females developing early-onset breast cancer or ovarian cancer and the male carrier developing prostatic cancer, whereas, in the other family, penetrance was incomplete and only breast cancer occurred, diagnosed at ages 38-81 years. Two novel nonsense mutations led to the loss of mutant BRCA1 transcript in families with 10 and 6 cases of early-onset breast cancer and ovarian cancer. A 665-nt segment of the BRCA1 3'-UTR and 1.3 kb of genomic sequence including the putative promoter region were invariant by single-strand conformation analysis in 13 families without coding-sequence mutations. Overall in our series, BRCA1 mutations have been detected in 26 families: 16 with positive BRCA1 lod scores, 7 with negative lod scores (reflecting multiple sporadic breast cancers), and 3 not tested for linkage. Three other families have positive lod scores for linkage to BRCA2, but 13 families without detected BRCA1 mutations have negative lod scores for both BRCA1 and BRCA2.