APOE and Alzheimer disease: Importantly, the AD causal risk pathway has 60% microglia related genes in its gene set (Cd33, Psen2, Psmb9, Apoe, Trem2, Psmb8, Spi1, Clu, C4a) and its up-regulated DEGs (C4a, Trem2, Cd33) overlapped with activated microglia pathway (Figure 6E).