APOE and Alzheimer disease: The Apolipoprotein (APOE) E4 allele is the strongest genetic risk factor for late onset Alzheimer's disease (AD), where possession of one E4 allele increases risk of AD by ∼3–4 times, and two alleles by ∼12–14 times compared to the AD-neutral E3/E3 genotype (Belloy et al., 2019; Farrer et al., 1997).