Studies of the contribution of defective MMR to the development of urothelial carcinomas, assessed using MSI analysis, loss of MMR protein expression, and MMR gene mutations, have found a low frequency (<10%) of MMR defects in urothelial carcinomas of the urinary bladder [15], but have indicated a high frequency (15–45%) of MMR defects in UUC [16-19]. The gene discussed is MRC1; the disease is bladder transitional cell carcinoma.