GFAP and Alzheimer disease: In the association analysis among the AD biomarkers, the NfL concentration showed a mild positively correlation with the concentrations of Aβ42 (r = 0.324, p = 0.205), Aβ40 (r = 0.386, p = 0.126), and GFAP (r = 0.531, p = 0.021) (Figures 3B–D).