DAO and schizophrenia: The case is supported by findings that patients have increased DAO activity and expression (Kapoor et al., 2006; Verrall et al., 2007; Burnet et al., 2008a; Madeira et al., 2008), complemented by equivocal evidence for lower D-serine levels (Hashimoto et al., 2003; Bendikov et al., 2007; Brouwer et al., 2013) and initial findings that novel DAO inhibitors show efficacy in preclinical models of schizophrenia (Adage et al., 2008) and, for sodium benzoate, in the disorder itself (Lane et al., 2013).