In schizophrenia patients, D-Ser levels are decreased in cerebrospinal fluid (Hashimoto et al., 2003; Bendikov et al., 2007), whereas DAAO protein and its activity are increased in the hippocampus and cerebrum (Madeira et al., 2008; Habl et al., 2009). The gene discussed is DAO; the disease is schizophrenia.