In addition to the above, the ε4 allele of the apolipoprotein E (ApoE) gene was identified as a strong risk factor for both early- and late-onset AD, where heterozygous carriers of the ε4 allele have an estimated threefold risk of developing AD and 15-fold risk in homozygous carriers of this allele [52–57]. This evidence concerns the gene APOE and Alzheimer disease.