Of interest, it was suggested that MBD4 exclusively acts as a tumor suppressor in MMR proficient mice as loss of MBD4 did not affect tumor onset or mutation frequency in Mlh1−/− or Msh2−/− mice (138), although the source of the MBD4 knockout mice in this study, and whether these may have retained glycosylase activity, has not been disclosed. This evidence concerns the gene MBD4 and neoplasm.