Apolipoprotein E (ApoE) is also considered an AD-associated ligand of TREM2 (Atagi et al., 2015; Bailey et al., 2015; Yeh et al., 2016) because the APOE genotype is a strong risk factor for late-onset AD (Corder et al., 1993). The gene discussed is APOE; the disease is Alzheimer disease.