APOE and Alzheimer disease: Numerous sporadic AD risk genes[18], including apolipoprotein E (ApoE), triggering receptor expressed on myeloid cells 2 (TREM2), Cluster differentiation(CD) 33, membrane-spanning 4-domains, subfamily A, member 6 A (MS4A6A), ATP-binding cassette, sub-family A, member 7 (ABCA7), and complement receptor 1 (CR1), are highly expressed in microglia and affect microglial phagocytosis of amyloid-beta peptides(Aβ).