APOE and Alzheimer disease: Genome-wide association studies (GWAS) have identified 30 genetic risk loci for AD, many of which are associated with microglial function, such as APOE and triggering receptor expressed on myeloid cells 2 (TREM2) variants (Efthymiou and Goate, 2017; Kunkle et al., 2019; Nguyen et al., 2020).