GFAP and early-onset autosomal dominant Alzheimer disease: Blood‐based biomarkers for Alzheimer's disease (AD), including amyloid beta (Aβ), tau, neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP), circulating molecular signatures of the amyloid, tau, and neurodegeneration (ATN) and inflammation, support their use in research and in clinical settings.1