There are three common APOE alleles, namely APOE ε2, ε3, and ε4 alleles, among which the APOE ε4 genotype is mainly associated with the higher risk of AD development (Mahley and Rall, 2000; Giri et al., 2016; Swerdlow et al., 2017). The gene discussed is APOE; the disease is Alzheimer disease.