MAPT and early-onset autosomal dominant Alzheimer disease: In a longitudinal observational study, Kwan, Arfaie et al. used [18F]-MK-6420, a high-affinity tau-PET tracer, to provide evidence that the presence of tau in the medial temporal lobe predicts longitudinal memory decline in cognitively normal elderly individuals during the preclinical phase of Alzheimer’s disease.