There is moderate evidence that Dao is a susceptibility gene for the disorder (Chumakov et al., 2002; Allen et al., 2008; Shi et al., 2008; Sun et al., 2008), while Dao expression and DAO activity are elevated in the brains of patients with schizophrenia (Kapoor et al., 2006; Verrall et al., 2007; Burnet et al., 2008; Madeira et al., 2008; Habl et al., 2009; Ono et al., 2009). This evidence concerns the gene DAO and schizophrenia.