IL17A and inflammatory bowel disease: In contrast to these microbiome similarities, host gene regulation shows distinct alterations across the three GI disorders; for example, unique antibacterial gene expression profile and disruption of the purine salvage pathway are specific to IBS, deregulation of proinflammatory IL-23/IL-17 signalling is unique to IBD, and prominent activation of oncogenic pathways such as Notch and WNT signalling is a hallmark of CRC8,13,100,101.