The objectives of this PET study were to determine the effects of varying multiple oral doses of sembragiline at steady state on brain MAO-B enzyme activity in patients with mild-to-moderate AD using PET imaging with [11C]-L-deprenyl-D2, and to characterise the sembragiline plasma–brain MAO-B inhibition relationship in patients with AD compared to healthy age-matched controls. This evidence concerns the gene MAOB and Alzheimer disease.