TREM2 and Alzheimer disease: Regarding the relation of TREM2 with OS, it has been supposed that a down-regulation of microglial TREM2 expression and signaling might be one of the major pathogenetic mechanisms in sporadic cases of AD in which advanced age, OS, neuroinflammation contribute to the suppression of wild-type TREM2, considering that TREM2 mutation is rare in humans [123].