A total of 63 MBCs, comprising 26 cases with germline mutations (germline-mutated MBCs), including 16 BRCA2, 6 BRCA1, 2 PALB2, 1 RAD50, 1 RAD51D, and 37 cases without germline mutations (non-mutated MBCs) were analyzed. The gene discussed is RAD50; the disease is maternal uniparental disomy of chromosome 20.