In analogy with the results of western blot and PCR analyses, it was found that, compared with the control group, expression of small intestinal as well as colonic mucosal claudin-1 protein in the diarrhea-predominant group was significantly decreased (P<0.05), while that in the constipation-predominant group was significantly increased (P<0.05), and the differences between the two IBS groups were significant (P<0.05), as shown in Table II and Fig. 5. This evidence concerns the gene CLDN1 and irritable bowel syndrome.