GFAP and early-onset autosomal dominant Alzheimer disease: Emerging evidence suggests that these plasma biomarkers (GFAP, NfL, pTau181, Aβ42/40) reflect processes of brain aging, even in cognitively healthy individuals, by capturing subtle neurobiological changes linked to neuroinflammation, axonal integrity, cerebrovascular function, and early Alzheimer-disease related pathobiology.