APOE and Alzheimer disease: In the present study, after adjusting for age, sex, and APOE alleles, the level of plasma Aβ42/Aβ40 showed a decreasing tendency but not a significant difference in patients with probable AD; meanwhile, the individual levels of plasma Aβ42 and Aβ40 were not significantly different from those of controls, which was consistent with the previous study (Olsson et al., 2016).