Germ-line mutations in predisposing genes, mainly BRCA1 (MIM 113705) and BRCA2 (MIM 600185) but also other genes critical for genome integrity such as CHEK2, PALB2, ATM, p53, PTEN, STK11, CDH1 and more, are responsible for about half of familial breast cancer cases, which in turn represent one-third of all breast cancers (Walsh and King, 2007). The gene discussed is BRCA1; the disease is breast cancer.