β-Amyloid is associated with aberrant metabolic connectivity in subjects with mild cognitive impairment

Positron emission tomography (PET) studies using [F-18]2-fluoro-2-deoxyglucose (FDG) have identified a well-defined pattern of glucose hypometabolism in Alzheimer's disease (AD). The assessment of the metabolic relationship among brain regions has the potential to provide unique information regarding the disease process. Previous studies of metabolic correlation patterns have demonstrated alterations in AD subjects relative to age-matched, healthy control subjects. The objective of this study was to examine the associations between beta-amyloid, apolipoprotein E epsilon 4 (APOE epsilon 4) genotype, and metabolic correlations patterns in subjects diagnosed with mild cognitive impairment (MCI). Mild cognitive impairment subjects from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study were categorized into beta-amyloid-low and beta-amyloid-high groups, based on quantitative analysis of [F-18]florbetapir PET scans, and APOE epsilon 4 non-carriers and carriers based on genotyping. We generated voxel-wise metabolic correlation strength maps across the entire cerebral cortex for each group, and, subsequently, performed a seed-based analysis. We found that the APOE epsilon 4 genotype was closely related to regional glucose hypometabolism, while elevated, fibrillar beta-amyloid burden was associated with specific derangements of the metabolic correlation patterns.