Several susceptibility genes for schizophrenia have been detected in recent years, including DTNBP1, neuregulin 1 (NRG1), catechol-O-methyltransferase (COMT), disrupted-in-schizophrenia 1 (DISC1), regulator of G-protein signalling 4 (RGS4), G72, proline dehydrogenase (PRODH), and D-amino acid oxidase (DAAO) [42-44]. Here, DAO is linked to schizophrenia.