PIK3CA and neurodegenerative disease: KEGG pathway analysis identified several pathways implicated in the pathophysiology of major depressive disorder (MDD), including cancer pathways, neuroactive ligand–receptor interactions, the PI3K-Akt signaling pathway, the cAMP signaling pathway, the calcium signaling pathway, neurodegenerative disease pathways, proteoglycans in cancer, chemical carcinogenesis-receptor activation, the MAPK signaling pathway, and the Alzheimer’s disease signaling pathway.