BRCA1 and breast cancer: In familial linkage studies, several high-penetrance low-frequency mutations in genes confer increased susceptibility to breast cancer [4], including breast cancer 1 gene (BRCA1), BRCA2, ataxia-telangiectasia mutated gene (ATM), etc.; however, these causative mutations explain only approximately 25% of the familial risk [5] and almost 5% of breast cancer incidence.