A 40-kb duplication of a region upstream of GREM1 has been associated with hereditary mixed polyposis syndrome (HMPS) [39], and a 16-kb duplication in the regulatory region of GREM1 has been found as the disease-causing genetic alteration in a family with attenuated/atypical polyposis syndrome [40]. Here, GREM1 is linked to hereditary mixed polyposis syndrome.