TREM2 and Alzheimer disease: For example, rare variants in the microglial phagocytic receptor gene TREM2 are associated with increased risk of AD, FTD, and PD, and loss of TREM2 function exacerbates Aβ-, tau-, and α-synuclein-associated neurotoxicity (Griciuc et al., 2019; Guo et al., 2019; Leyns et al., 2019; Zhao et al., 2018).