According to a study conducted in patients with chronic schizophrenia (n = 51), compared with healthy control subjects (n = 45), the KYNA/3-HK ratio and IL-4 levels, but not soluble IL-2 receptor (sIL-2R) and IFN-α levels, were consistently decreased in schizophrenia patients at all analyzed time points (at time of admission, after a 4-week treatment and remission). This evidence concerns the gene IL4 and schizophrenia.