Compared with the most common allele, APOE3, the APOE2 allele has been reported to provide protective effects (Reiman et al., 2020), whereas APOE4 increases the risk of late-onset sporadic AD by 3-fold for heterozygous carriers and 15-fold for homozygous carriers (Raber et al., 2004; Smith et al., 2019a). This evidence concerns the gene APOE and Alzheimer disease.