TREM2 and Alzheimer disease: Although their specific roles in AD pathogenesis remain incompletely elucidated, many of these genes appear to be involved in immune regulation (e.g., CR1, CD33, PLCG2), endocytosis/phagocytosis/membrane trafficking (BIN1, PICALM, TREM2, ABI3), or lipid metabolism (APOE, CLU, ABCA7, INPP5D) (For a comprehensive overview of these genes’ functions, readers are referred to previous reviews [6, 7]).