XPNPEP1 and Crohn disease: This and other animal models of Crohn’s disease, including the senescence accelerated prone mouse (SAMP) and the mouse downregulated in adenoma (mdra) deficient mouse have shown increased small intestinal permeability well before disease expression.25–27 This study extends these observations in an important manner by demonstrating that reversal of this barrier defect can attenuate the disease, implying that the increased permeability is not simply an epiphenomenon but rather is an important aetiological event.