Nevertheless, most patients with late-onset AD do not carry familial AD mutations and instead, express genetic risk factors associated with immune-related networks, particularly in genes expressed by microglia such as TREM2, CD33, and C1R (Efthymiou and Goate, 2017; Hansen et al., 2018; Schwabe et al., 2020). Here, TREM2 is linked to Alzheimer disease.