GFAP and Alzheimer disease: We tested this hypothesis by comparing FN1 and GFAP (marker for reactive gliosis) levels in APOEε3/3 (control, n = 2), APOEε4/4 AD (n = 2), and APOEε4/4 unaffected (n = 6) individuals (Fig. 6, Supplementary Table 8, Supplementary Dataset 3).