The importance of the epithelial barrier function in IBD pathogenesis has also been highlighted through GWAS studies where early studies identified a Crohn’s disease associated mutation in DLG5, impairing DLG5 to function as a guanylate kinase and altering the epithelial polarity [51], and polymorphisms in OCTN1, the organic cation/L-carnitine transporter involved in intestinal uptake [52]. The gene discussed is DLG5; the disease is irritable bowel syndrome.