In Reply Dr Gao and colleagues suggest that the ratio of CSF tau to Aβ42 may be a more useful indicator of subsequent risk of cognitive decline than Aβ42 alone. Although we agree that the ratio may be a better predictor of decline, because CSF tau elevation indicates neurodegeneration and therefore marks a presumed downstream effect of amyloid,1 our purpose was to examine the value of amyloid accumulation alone, in part to support the use of amyloid biomarkers to select populations for clinical trials of antiamyloid interventions. For such trials, selecting a population with tau elevation will predict greater decline, but perhaps not greater treatment response, because earlier intervention may be preferable.2
Donohue MC, Aisen PS. Elevated Brain Amyloid in Cognitively Normal Individuals—Reply. JAMA. 2017;318(14):1393–1394. doi:10.1001/jama.2017.12962
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