GPR18 and major depressive disorder: A bioinformatics analysisfurther identified autophagy-related genes, such asG protein-coupled receptor 18 (GPR18),pyruvate dehydrogenase kinase 4 (PDK4), neuregulin 1 (NRG1), and EPH receptor B2 (EPHB2), as potential diagnostic markersfor MDD, with GPR18 possibly playing a role in its pathogenesis [20].