SLC22A4 and ulcerative colitis: The association between the L503F nonsynonymous variant of the organic cation transporter OCTN1/SLC22A4 and IBD is well established in both Crohn’s disease (CD)5 and ulcerative colitis (UC).5,6 OCTN1 is expressed ubiquitously; and in the intestine, it is located at the brush border membrane of enterocytes where it contributes to the intestinal absorption of several dietary substrates.7 The OCTN1 ability to interact with hexogen molecules other than human metabolites suggests its possible role in mediating host/microbiota cross-talk.