First- and second-generation antipsychotics, beyond the well-defined action on dopaminergic and serotonergic receptors, have been seen to exert an in vitro inhibitory effect on DAO activity, which should be considered as a part of the drug mechanism of action, providing further evidence to support the putative involvement of the oxidase in the pathogenesis of schizophrenia [299,300,301]. This evidence concerns the gene DAO and schizophrenia.