As the cancers in such families were diagnosed significantly earlier than in women who developed sporadic breast or ovarian cancer, experts might also call the newly identified gene BRCA3
They may represent a diverse group of families with the hypothetical BRCA3
gene, families with genes of lower penetrance, families with mutations in high-penetrance genes that are very rare, or just families with BRCA1 or 2 mutations that were missed by the methods employed.
A third major genetic locus, the putative BRCA3
, has not been defined to account for other familial breast cancer cases.
Inherited alterations in BRCA1, BRCA2 and the newly discovered BRCA3
gene increase a person's lifetime risk of developing breast and ovarian or prostate cancer.
Such mutations, provided that they exist, would be akin to BRCA3
, 4, 5, and so forth.
(31) It is likely that there are other genes yet to be discovered that affect breast cancer risk in families negativ e for BRCA1 or BRCA2 mutations, some of which may be high penetrance genes that confer significantly increased risk such as a putative BRCA3
gene, (32) and others that are low-penetrance and confer moderately increased risk such as CHEK2.