Recent advances in blood plasma assays of Alzheimer’s disease amyloid and tau pathology have enabled detection of Alzheimer’s disease pathophysiology during life, but it remains unclear when plasma biomarker abnormalities are detectable relative to established amyloid and tau PET imaging biomarkers, and the extent to which plasma biomarkers can be used for biological disease staging. Here, MAPT is linked to early-onset autosomal dominant Alzheimer disease.