Both mice with a heterozygous or homozygous loss of Dnmt1 (Math1-cre::Dnmt1Fl/+::SmoM2Fl/+ and Math1-cre::Dnmt1Fl/Fl::SmoM2Fl/+, respectively) showed a significant reduction in the number of proliferating tumor cells in the cerebellum at P5, as compared to Math1-cre::SmoM2Fl/+ mice (Fig. 4a,b). The gene discussed is DNMT1; the disease is neoplasm.