GFAP and early-onset autosomal dominant Alzheimer disease: Previous studies have suggested that plasma GFAP could be used as an earlier marker than tau PET in hypothetical models of Alzheimer's disease progression.12,26 Results in the previous section concur with these results by showing that GFAP mediates the effect of amyloid deposition on tau pathology, in line also with earlier studies concluding that astrocytic activation could facilitate tau pathology spread.