Complementarily, PET work with R-11C-verapamil demonstrates that P-glycoprotein-mediated efflux at the BBB declines with aging and is impaired in Alzheimer’s disease, implying greater brain exposure to BBB-permeant α1-blockers in vulnerable populations [48,49]. This evidence concerns the gene ABCB1 and early-onset autosomal dominant Alzheimer disease.