APOE and Alzheimer disease: In FAD, the lifetime risk of dementia is very high, nearly 100% (Bateman et al. 2011), while in SAD, the percentage is lower, about 22%–95% in APOE ε4-related AD and 7%–35% in APOE ε4-unrelated AD (Genin et al. 2011; Reiman et al. 2020).