Plasma GFAP is increased in response to abnormal brain Aβ accumulation very early in the AD continuum and partly mediates the association between Aβ-PET and tau-PET.22,23,24 Our primary outcome was positivity on tau-PET, and we also investigated associations of plasma biomarkers with Aβ-PET measures and cognitive function. Here, GFAP is linked to Alzheimer disease.