GREM1 and hereditary mixed polyposis syndrome: Gremlin 1 expression is upregulated in intestinal epithelial cells of patients with hereditary mixed polyposis syndrome characterized by the development of multiple types of colorectal tumors, which provides Lgr5− cells excluded from the stem cell niche with stem-like properties by disrupting the homeostatic Gremlin 1 gradient at the crypt base-villus axis [211].