TREM2 and Alzheimer disease: In contrast to the Trem2-independent formation of PAM microglia, which facilitate the phagocytosis of oligodendrocytes and OPCs during white matter development (Li et al., 2019), a Trem2-dependent subset of white matter-associated microglia (WAM) have been described in the context of aging and AD (Safaiyan et al., 2021).