More recently, two studies showed that expression and subcellular distribution of the tight junction proteins, ZO-1, occludin and claudin-1 were found to be altered in IBS-C and IBS-D [31] and that paracellular permeability was significantly higher in cecal biopsies from IBS patients compared to controls, with similar increases in all IBS subtypes (−C, −D and −M) [32]. This evidence concerns the gene CLDN1 and irritable bowel syndrome.