PSEN1 and Alzheimer disease: Work in Psen1 mice, a model of Aβ pathology, found that knockdown of TREM2 in the early to middle stages of AD was beneficial as it inhibited microglial phagocytosis of synapses, while this same approach in middle to late stages was detrimental by impairing microglial phagocytosis of Aβ (Sheng et al., 2019).