GFAP and Alzheimer disease: In plasma, age was associated with NfL levels in the controls (rho = 0.608, p < 0.001), with p-tau181 values in AD (rho = − 0.313, p = 0.002), and with GFAP concentrations in FTD (rho = 0.366, p = 0.005) and PSP (rho = 0.596, p < 0.001) groups.