APP and Alzheimer disease: A recent study suggests that presenilin increases microglial phagocytosis of Aβ, and this γ-secretase has dual role for AD pathogenesis: one is cleavage of amyloid precursor protein (APP) to produce pathologic Aβ, and the other is reduction of microglial phagocytosis of Aβ by γ-secretase inhibitor [117].