This unique amino acid can be metabolized by the gut microbiota into a range of indolic compounds, some of which can activate key homeostatic receptors such as the aryl hydrocarbon receptor (AhR) or the Pregnane X receptor (PXR).87 Indeed, these receptors have been implicated in intestinal inflammation and microbial tryptophan metabolism is altered in patients with IBD and CeD.113–116 Thus, microbial proteases could indirectly modulate different intestinal conditions by modifying common dietary antigens or facilitating the release of bioactive metabolites in the gut. The gene discussed is NR1I2; the disease is cranioectodermal dysplasia.