Because an MBD4 defect is expected to lead to C:G > T:A transition mutations in the context of CpG sites [3], we analyzed the data deposited in the COSMIC database v72 [34] to investigate the average number of C:G > T:A transitions in CRC tumors with MBD4 pathogenic (frameshift) variants, MLH1 pathogenic variants or combined MBD4 plus major MMR gene variants (MLH1, MSH2 and MSH6) and, as controls, CRC tumors with no MBD4 or major MMR gene variants. The gene discussed is MLH1; the disease is colorectal carcinoma.