CLDN1 and irritable bowel syndrome: According to the results of the current study, compared with those in the control group, claudin-1 protein levels in the small intestine and colon mucosa in constipation-predominant IBS group were significantly increased (P<0.05), while expression was decreased in the diarrhea-predominant IBS group (P<0.05), the results of which were consistent among FQ-PCR, western blot and immunohistochemical analyses.