GAD2 and Alzheimer disease: Hub gene analyses also revealed the downregulation of synaptic genes encoding postsynaptic receptors, transporters and enzymes mediating glutamatergic transmission (e.g. GRIA1, GRIA2, GRIN2A and SLC17A6) or GABAergic transmission (e.g. GAD2, GABRB2 and SLC6A1) in Alzheimer’s disease (Fig. 1E).