Genetic studies in humans showed that rare variants in the TREM2 gene are associated with an exceptionally increased risk of AD, comparable to increase in risk by the APOE ε4 genotype (Guerreiro & Hardy, 2013; Jonsson et al, 2013), suggesting that TREM2‐related microglia activation may reduce the risk of AD dementia. Here, TREM2 is linked to Alzheimer disease.