GAD1 and schizophrenia: In addition, a study of patients with schizophrenia demonstrated that GABA-synthesizing enzyme glutamate decarboxylase 67 (GAD67) content is lower in PV cells, and that their network activity (i.e., γ oscillations) is impaired, suggesting a link between GAD67 in PV cells and γ oscillations (Lisman et al., 2008).