MAPT and early-onset autosomal dominant Alzheimer disease: Blood‐based phosphorylated tau 217 (p‐tau217), glial fibrillary acidic protein (GFAP), and neurofilament light chain (NfL) show promise for Alzheimer's disease (AD), while their links to brain amyloid beta (Aβ)/tau, hippocampal atrophy, and cognitive decline need further investigation.