TREM2 and Alzheimer disease: Indeed, several genomic analyses suggest the involvement of microglia in AD: (1) the first reports on pathway enrichment analyses indicated the involvement of innate immunity in AD [81]; (2) as previously mentioned, these analyses highlighted the regulation of endocytosis (which is essential for phagocytosis) [64, 81]; (3) a large part of GWAS-define genes are expressed in microglia [45] (Fig. 1); and (4) a major genetic discovery indicated that non-synonymous variants in TREM2, ABI3 and PLCγ2 were associated with AD risk [40, 65, 120].