TREM2 and Alzheimer disease: In TREM2−/−5xFAD mice, microglia failed to cluster around Aβ plaques, resulting in less effective Aβ phagocytosis and clearance (Wang et al., 2015; Ulland et al., 2017), a result that has been replicated in AD patients carrying TREM2 risk variants (Ulland et al., 2017).