GAD1 and schizophrenia: Specifically, post-mortem gene expression studies and in vivo plasma detection have demonstrated that Egr1 is down-regulated in prefrontal cortex of schizophrenia patients in a fashion that is directly correlated with decrease in GAD1 (glutamate decarboxylase 1, the enzyme that is responsible for GABA production), and plasma levels were reduced, therefore supporting the view that Egr1 may be a potential biomarker of the disease (Kimoto et al., 2014).