Time between milestone events in the Alzheimer's disease amyloid cascade.

ABSTRACT

OBJECTIVE: Estimate the time-course of the spread of key pathological markers and the onset of cognitive dysfunction in Alzheimer's disease. METHODS: In a cohort of 335 older adults, ranging in cognitive functioning, we estimated the time of initial changes of Aß, tau, and decreases in cognition with respect to the time of Aß-positivity. RESULTS: Small effect sizes of change in CSF Aß42 and regional Aß PET were estimated to occur several decades before Aß-positivity. Increases in CSF tau occurred 7-8 years before Aß-positivity. Temporoparietal tau PET showed increases 4-5 years before Aß-positivity. Subtle cognitive dysfunction was observed 4-6 years before Aß-positivity. CONCLUSIONS: Increases in tau and cognitive dysfunction occur years before commonly used thresholds for Aß-positivity. Explicit estimates of the time for these events provide a clearer picture of the time-course of the amyloid cascade and identify potential windows for specific treatments.