APOE and Alzheimer disease: For sαKl, associations with biomarkers were non-significant except for a negative association of serum sαKl with P-tau181 in aMCI-AD (β = −0.25, p = 0.036) and a positive association with Aβ42/40 ratio in APOE ε4 non-carriers (β = 0.24 p = 0.047).