DAO and schizophrenia: Several schizophrenia candidate genes that affect NMDAR signalling have been identified, including GRIN1, GRIN2A, GRIN2B and GRIN2D, which are genes encoding the GluN1, GluN2A, GluN2B and GluN2D subunits of the NMDAR, respectively, as well as the gene encoding D-amino acid oxidase (DAAO), which regulates the availability of D-serine, a co-agonist at NMDARs [11,104,105,106].