Compared with controls (mean [SD] age, 63 [8] years), AD groups were older (amyloid-positive cognitively unimpaired: mean [SD] age, 67 [9] years; amyloid-positive MCI: mean [SD] age, 67 [7] years; amyloid-positive dementia: mean [SD] age, 65 [8] years; P = .03) and were more likely to carry an APOE4 allele (control: 27 individuals [32.5%]; amyloid-positive cognitively unimpaired: 21 individuals [67.7%]; amyloid-positive MCI: 23 individuals [76.7%]; amyloid-positive dementia: 35 individuals [66.0%]; P < .001). This evidence concerns the gene APOE and Alzheimer disease.