MSH2 and neoplasm: 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.