Prior cross-sectional studies have shown that that higher NfL [7, 16], GFAP [5, 17], pTau-181 [18], and lower Aβ42/40 [5] in blood were associated with smaller brain volume in regions vulnerable to AD (e.g., hippocampus, entorhinal cortex), as well as white matter volume [19]. Here, GFAP is linked to Alzheimer disease.