One of the important findings from the study was that the KYN/TRP ratio was significantly increased in schizophrenia patients, indicating increased IDO activity with a large effect size in CNS, small effect size in serum and nonsignificant effect size in plasma, implicating that the plasma KYN/TRP ratio should not be used as an indicator of IDO activity. This evidence concerns the gene IDO1 and schizophrenia.