Genome-wide association studies (GWASs) have robustly identified numerous AD risk loci, such as TREM2 and CD33, which are predominantly expressed in microglia, positioning these cells as critical mediators of disease susceptibility (Wightman et al., 2021; Guerreiro et al., 2013; Jonsson et al., 2013). Here, TREM2 is linked to Alzheimer disease.