GFAP and Alzheimer disease: In this study, we investigated the association between NPS and glial markers (microglial activation and astrocyte reactivity), in living individuals across the aging and AD continuum using the Neuropsychiatric Inventory Questionnaire (NPI-Q); positron emission tomography (PET) biomarkers of Aβ, tau, and microglial activation; and plasma glial fibrillary acidic protein (GFAP) as measures of astrocyte reactivity.