APOE and Alzheimer disease: Consistent with a prolonged preclinical disease stage, a number of investigations, including studies from our group, have shown that positron emission tomography (PET) measures of cerebral glucose metabolism vary according to AD genetic risk (apolipoprotein E ε-4 [ApoE-ε4]) and predict cerebral metabolic and cognitive decline in people with mild cognitive complaints (age-associated memory impairment) [15]–[17].