Evidence that DAO contributes to the glutamatergic dysfunction in schizophrenia is threefold (Verrall et al., 2010; Labrie et al., 2012; Sacchi et al., 2013): it may be a susceptibility gene (Chumakov et al., 2002; Allen et al., 2008; Shi et al., 2008; Sun et al., 2008); DAO expression and activity are increased (Kapoor et al., 2006; Verrall et al., 2007; Burnet et al., 2008a; Madeira et al., 2008); and DAO inhibitors show preliminary preclinical (Adage et al., 2008) and clinical (Lane et al., 2013) evidence for therapeutic efficacy. The gene discussed is DAO; the disease is schizophrenia.