TREM2 and Alzheimer disease: Transcriptomic analysis of AD mice revealed that a gradual transition of microglia from a disease-associated state is regulated by the downregulation of homeostatic genes and upregulation of Apolipoprotein E (APOE) and triggering receptor expressed on myeloid cells 2 (TREM2), which emphasizes the essential roles of TREM2 in AD pathogenesis (98).