Brain amyloid and the transition to dementia in Down syndrome.

INTRODUCTION: Down syndrome (DS) is associated with elevated risk for Alzheimer's disease (AD) due to amyloid beta (Aß) lifelong accumulation. We hypothesized that the spatial distribution of brain Aß predicts future dementia conversion in individuals with DS. METHODS: We acquired 18F-florbetapir positron emission tomography scans from 19 nondemented individuals with DS at baseline and monitored them for 4 years, with five individuals transitioning to dementia. Machine learning classification using an independent test set determined features on 18F-florbetapir standardized uptake value ratio maps that predicted transition. RESULTS: In addition to "AD signature" regions including the inferior parietal cortex, temporal lobes, and the cingulum, we found that Aß cortical binding in the prefrontal and superior frontal cortices distinguished subjects who transitioned to dementia. Classification did well in predicting transitioners. DISCUSSION: Our study suggests that specific regional profiles of brain amyloid in older adults with DS may predict cognitive decline and are informative in evaluating the risk for dementia.

Down syndrome: Distribution of brain amyloid in mild cognitive impairment.

INTRODUCTION: Down syndrome (DS) is associated with a higher risk of dementia. We hypothesize that amyloid beta (Aß) in specific brain regions differentiates mild cognitive impairment in DS (MCI-DS) and test these hypotheses using cross-sectional and longitudinal data. METHODS: 18F-AV-45 (florbetapir) positron emission tomography (PET) data were collected to analyze amyloid burden in 58 participants clinically classified as cognitively stable (CS) or MCI-DS and 12 longitudinal CS participants. RESULTS: The study confirmed our hypotheses of increased amyloid in inferior parietal, lateral occipital, and superior frontal regions as the main effects differentiating MCI-DS from the CS groups. The largest annualized amyloid increases in longitudinal CS data were in the rostral middle frontal, superior frontal, superior/middle temporal, and posterior cingulate cortices. DISCUSSION: This study helps us to understand amyloid in the MCI-DS transitional state between cognitively stable aging and frank dementia in DS. The spatial distribution of Aß may be a reliable indicator of MCI-DS in DS.