MAPT and Alzheimer disease: Using the average Δ[18F]FDG uptake in the mediobasal temporal cortex as a surrogate marker, a study population enriched by including those with both biomarkers above the proposed thresholds ([18F]florbetapir SUVR >1.228 and p-tau >45 pg/ml) would require 87 individuals with preclinical AD per trial arm to test a 25% drug effect (80% of power at a 5% level) over 2 years.