p-tau181 differentiating:1. Cohort 1: - tau-positive vs. negative AuROC = 0.87 with tau-PET as reference; - AD vs. non-AD dementia: AuROC = 0.94 with clinical diagnosis 2. Cohort 1 and cohort 2 together: - Aβ + vs. Aβ-participants: AuROC = 0.80 with Aβ PET as reference 3. Cohort 3: - AD vs. non-AD dementia: AuROC = 0.85 neuropathological reference. The gene discussed is MAPT; the disease is Alzheimer disease.