GFAP and early-onset autosomal dominant Alzheimer disease: In this study, we explore how regional brain metabolism, as measured by fludeoxyglucose-18 (FDG)-PET, relates to plasma biomarkers such as p-tau217, Glial fibrillary acidic protein (GFAP), phosphorylated-tau (p-tau)217/beta-amyloid (Aβ) 42, and Aβ42/40 in a cohort of participants with early symptomatic Alzheimer's disease.