GREM1 and polyp: Our previous work had generated a disease-positioned mouse model of HMPS called Vil1-Grem1 using the Villin1 promoter to drive aberrant intestinal epithelial expression of the secreted BMP antagonist Grem1. This induces a pronounced murine pan-intestinal polyposis in adult mice (median survival 250 days) with lesions that phenocopy the mixed polyp histology of the human condition, including the formation of ectopic crypts, best seen within the villus in small intestinal lesions12.