Several studies reported that the rare TREM2 mutation, arginine 47 to histidine (p.R47H, rs75932628) substitution in the extracellular immunoglobulin domain, significantly increases the risk for AD with odds ratios similar to those of carrying an apolipoprotein E (APOE) ε4 allele (Guerreiro et al., 2013; Jonsson et al., 2013), which is present in about half of late-onset AD (LOAD) patients and has been convincingly demonstrated to affect its risk (Bertram et al., 2010). The gene discussed is APOE; the disease is Alzheimer disease.