Four other risk genes—dysbindin (DTNP1), neuregulin 1 (NRG1), neuregulin 2 (NRG2), and the NRG1/2-receptor ErbB4 (ERBB4)—are implicated in regulating NMDAR function and synaptic plasticity, and their expression is altered in post-mortem tissue in schizophrenia: downregulation of DTNP1 in hippocampal and cortical tissue has been reported in schizophrenia patients, and Dtnp1 knockout in mice leads to reduced expression of NMDARs and correlates with working memory impairments (31, 32). The gene discussed is ERBB4; the disease is schizophrenia.