In mice models lacking intestinal epithelial core 1 O-glycans (IEC C1GALT1−/− mice) or gastric epithelial O-glycans (GEC C1galt1−/− mice), spontaneous colitis and gastritis, as well as gastric or colon tumors, were developed, respectively (Fu et al. 2011; Bergstrom et al. 2016; Liu et al. 2020). The gene discussed is C1GALT1; the disease is colitis.