TREM2 and Alzheimer disease: Similar plaque morphology with less fibrillar Aβ, as observed in APP-KI mice, has also been reported in AD mice deficient for TREM2 or APOE that also have less microglial cells recruited to amyloid plaques and display prominent neuritic dystrophies (Parhizkar et al., 2019; Sala Frigerio et al., 2019; Ulrich et al., 2018; Wang et al., 2015; Yuan et al., 2016).