GFAP and Alzheimer disease: In controls, significant positive correlations were found between complement and AT(N) biomarker levels: clusterin/NfL; sCR1/GFAP, sCR1/NfL; C1q/Aβ40, while in the AD group there were significant negative correlations between clusterin/Aβ40, clusterin/Aβ42 (Additional file 1: Table S2).