About 15% of inherited breast cancer cases may be due to segregation of rare germline mutations [minor allele frequency (MAF) ≤ 1%] in high-penetrance [i.e., relative risk (RR) > 10] susceptibility genes such as BRCA1, BRCA2, TP53, and PTEN2,3. The gene discussed is BRCA1; the disease is breast cancer.