APOE and Alzheimer disease: By definition, APOE ε4 carriers are at elevated risk for AD; accordingly, they had slightly higher mean global Aβ (1.11 ± 0.10) than non-carriers (1.07 ± 0.08), and a greater proportion of amyloid-positive cases (though many ε4 carriers were still amyloid-negative, given their middle age).