Numerous studies have demonstrated that APOE ε4 is associated with an earlier age of disease onset (Blacker et al., 1997, Bonham et al., 2016, Frisoni et al., 1998, Sando et al., 2008), longevity (Deelen et al., 2019), and the existence of a gene-dosage effect between increasing copies of ε4 and lower age of AD onset (Corder et al., 1993). The gene discussed is APOE; the disease is Alzheimer disease.