KMO and schizophrenia: It has been hypothesized that a reduction in the quantity and activity of the enzymes kynurenine 3-monooxygenase (KMO) and 3-hydroxy-anthranilic acid oxidase (3HAO), along with a reduction in the quantity and activity of their corresponding mRNA, is the reason for the association between increased levels of kynurenic acid and schizophrenia.