APOE and Alzheimer disease: Nonetheless, the observations of plasma GFAP and Aβ1–42/Aβ1–40 ratios remaining significantly altered between Aβ− and Aβ+ participants within the APOE ε4 non-carrier subset from this exploratory analysis may be viewed as a beneficial feature for early AD biomarkers, given that the presence of the APOE ε4 allele in itself is a major risk factor for the disease.