Taken together, our results suggest that the aberrant methylation observed in the MGAT3 gene in CD3+ T cells from intestinal mucosa of UC patients, B cells from peripheral blood, and the whole peripheral blood in UC and CD patients is a possible mechanism underlying inflammation due to a change in the immune system—either through the change of glycans on Fc region of IgGs or by modulating the glycosylation profile of glycoproteins on intestinal T cells. Here, MGAT3 is linked to Cowden disease.