A rare inherited condition called hereditary mixed polyposis syndrome (HMPS) is caused by a 40 kb chromosomal duplication event on chromosome 15q13.3 upstream of the GREM1 gene that leads to 2500-fold upregulation of GREM1 mRNA production in the intestine of these patients (24). The gene discussed is GREM1; the disease is hereditary mixed polyposis syndrome.