Patients that developed hyperactive delirium during the first week of ICU treatment (n = 20) showed significantly lower CSF Per2 expression levels on day 1 compared to patients that did not develop early delirium (n = 14, CSF Per2 expression (fold induction vs. control) 0.17 ± 0.08 vs. 0.12 ± 0.12, p = 0.008, Figure 4c). The gene discussed is PER2; the disease is delirium.