While APOE ε4 heterozygotes have a two to four times increased lifetime risk of AD, homozygotes are at 14 times increased risk, such that 23% to 30% of APOE ε4 heterozygotes have developed AD by age 85 compared to 51% to 60% of APOE ε4 homozygotes.9 Here, APOE is linked to Alzheimer disease.