APOE and Alzheimer disease: The risk of AD increases in individuals with genotype APOE 2/4 (one allele is an APOE2 allele, the second allele is an APOE4 allele) with an odds ratio (OR) of 2.6, with an APOE 3/4 genotype with an OR of 3.2 and with an APOE 4/4 genotype with an OR of 14.9 [33, 34].