Compared with other cell types in the brain, many AD-related genetic variants are selectively or preferentially expressed in microglia, such as TREM2, APOE, CD33, INPP5D, MS4A6A, and PLCG2 (Srinivasan et al., 2016; Sarlus and Heneka, 2017; Hansen et al., 2018). Here, TREM2 is linked to Alzheimer disease.