GFAP and Alzheimer disease: In UCSF only, plasma GFAP significantly moderated the relationship between AD meta‐ROI volume and both memory (NMRI–Cogmemory: β [95% CI] = 0.20 [0.06, 0.35], p = 0.0064; J–N threshold > 110 pg/mL) and executive function (NMRI–Cogexecutive: β [95% CI] = 0.19 [0.00, 0.39], p = 0.048; J–N threshold > 98 pg/mL; Figure 4, Supplementary Results Table S4), such that the association between lower AD meta‐ROI volume and worse cognition only emerged when plasma GFAP exceeded ∼100 pg/mL.