APOE ε4 has been associated with a lower age of onset and elevated prevalence of AD, with the clinical onset age being 68 years in APOE ε4 homozygotes and 76 years in APOE ε4 heterozygotes, compared to 84 years of age in non-ε4 carriers [24,25]. The gene discussed is APOE; the disease is Alzheimer disease.