GLUD1 and schizophrenia: Ambient D-serine level is regulated by excitatory glutamatergic activity (Van Horn et al., 2017, Ma et al., 2014), and low D-serine levels are associated with epilepsy (Klatte et al., 2013) and schizophrenia-like behaviors (Ma et al., 2013), consistent with defects in synaptic inhibition and GluD1 function.