PTN and Alzheimer disease: In addition, many synaptic genes with reduced expression were identified as DEGs in astrocytes of both brain organoids and AD patient brains, such as GABA receptors (GABRA2 and GABRB1), glutamate receptors (GRIA1 and GRIA2), Glutamine synthetase (GLUL), neuronal membrane glycoprotein M6‐a (GPM6A), neuroligin‐1 (NLGN1), neurexin genes (NRXN1), and pleiotrophin (PTN) (Figure 7E).