The purpose of this investigation was, therefore, twofold: 1) to validate cross-radiotracer comparisons (PIB vs Florbetapir) in unrelated but matched patient populations and determine the comparability of amyloid PET data; and 2) to examine the distribution of amyloid-positive brain scans in different age groups, establish how age affects the discriminative power of amyloid PET imaging in those of advanced age (where >30 % of cognitively normal adults can be amyloid positive) and establish whether apolipoprotein ε4 (ApoE4) differentially mediates the Aβ load in AD patients at different ages. The gene discussed is APOE; the disease is Alzheimer disease.