PER1 and inflammatory bowel disease: When comparing clock protein expression in the intestinal mucosal epithelial cells of 24 patients with CD and 26 patients with UC and controls, the expressions of BMAL1, PER1, PER3, TIMELESS, and NPAS2 decreased in patients with IBD, while no significant differences were observed in BMAL2, CLOCK, and PER2 expression [51].