CLOCK and Crohn disease: Given the circadian clock influences gastrointestinal physiology and immunity, we hypothesized that the peripheral circadian clock is altered in these patients and might contribute to immune activation associated with IBD and IBS. To investigate this, RNA was extracted from whole blood obtained from control subjects (n = 29), IBD (n = 40 ulcerative colitis, n = 38 Crohn's disease) and IBS (n = 38) participants to investigate peripheral clock gene expression via quantitative PCR.