GAD1 and schizophrenia: Likewise, decreased levels of GAD67 mRNA and protein are consistently reported in the postmortem brains of schizophrenia patients (de Jonge et al. 2017; Fujihara 2023), with the reduction being most pronounced in parvalbumin-positive interneurons, suggesting a functional impairment in these cells (Hashimoto et al. 2009).