Even though a few studies indicate opposed effects for TREM2 levels in AD, lately, a study reported the level of soluble TREM2 (sTREM) directly linked with the early and delayed stage of AD [181, 182], where the peak beneficial role of TREM2 has observed in the early stage and later stage; its salutary effect gradually decreased (Figure 3). This evidence concerns the gene TREM2 and Alzheimer disease.