APOE and Alzheimer disease: Compared to homeostatic microglia, DAM demonstrate a reduction in the expression of microglia homeostatic genes, such as P2ry12/P2ry13, Cx3cr1, Cst3, Cd33, Csf1r, and Tmem119, and upregulation of a vast array of genes, including multiple known AD risk genes (Apoe, Lpl, Trem2, Tyrobp, and Ctsd) (Keren-Shaul et al., 2017; Table 1 and Figure 1).