Carriers of one germline copy of the epsilon4 (E4) allele of the apolipoprotein E gene (APOE4), present in ~15 to 20% of the population, have a threefold higher risk of AD, while two copies (~2 to 3% of the population) increase the risk by ~10 fold (Saunders et al., 1993; Murrell et al., 2006; Sando et al., 2008; Lumsden et al., 2020). The gene discussed is APOE; the disease is Alzheimer disease.