Changes in the number of EC cells and the levels of 5-HT in the serum samples from IBD patients have previously been documented.85,86 Colonic biopsy specimens from IBD patients also demonstrate an upregulation of 5-HTR3 and, more recently 5-HTR7 expression with associated increases in intestinal inflammation.87,88 Whilst this demonstrates a role for serotonin signaling in IBD pathogenesis, it remains to be seen if this also correlates with the development of chronic pain in these patients. This evidence concerns the gene HTR5A and irritable bowel syndrome.