Further, longitudinal tau PET is nowadays often used to study the effects of drugs directed against more upstream events in AD, such as Aβ, including whether such therapies can slow the accumulation and spread of tau, which could indicate a positive clinical effect beyond just target engagement.28 However, to use longitudinal tau PET effectively as an outcome in clinical trials, enrichment for individuals likely to show tau accumulation and spread during the trial is key. The gene discussed is MAPT; the disease is Alzheimer disease.