Genetic deficiencies in various circadian clock components (PER1/2, BMAL1, CLOCK, RORα, and REV‐ERBα) have been linked to an increased susceptibility of IBD mainly via influencing colonic permeability by regulating the integrity of the intestinal barrier [56, 83, 92, 171, 172, 173]. This evidence concerns the gene PER1 and inflammatory bowel disease.