CLDN1 and irritable bowel syndrome: Studies in patients with the diarrheal subtype of IBS have shown that miR-29a downregulates zonula occludens-1 (ZO-1) and claudin-1 (CLDN1) [17], while both miR-29a and miR-29b reduce the expression of CLDN1 and NF-κB repressing factor (NKRF) in intestinal tissue [59].