Many susceptibility genes preferentially expressed in microglia of the aged human brain (e.g., TREM2, CD33, SORL1, and INPP5D) were associated with AD (Olah et al., 2018), while genetic analysis also indicated that various immune-related genes were associated with AD risk (Karch and Goate, 2015). Here, TREM2 is linked to Alzheimer disease.