Those with an APOE2 allele (ɛ2/ɛ2 or ɛ2/ɛ3 genotypes) have a protective effect against AD compared to other APOE genotypes (ɛ2/ɛ4, ɛ3/ɛ3, ɛ3/ɛ4, ɛ4/ɛ4) [27]. This evidence concerns the gene APOE and Alzheimer disease.