Neuroimaging of individuals with Down's syndrome at-risk for dementia: evidence for possible compensatory events

BACKGROUND: We report functional and structural brain indicators that may precede the onset of dementia in individuals with Down's syndrome (DS). METHODS: Middle-aged adults with DS (n=19), a group known to be at high risk for dementia, were studied with (1) positron emission tomography (PET) to determine cerebral glucose metabolic rate (GMR), (2) structural magnetic resonance imaging (MRI) to determine gray matter volume (GM), and (3) ratings of potential dementia indicators based on a structured interview of caregiver observations designed to evaluate individuals with low intelligence. RESULTS: Although none of the participants showed clinical signs of dementia, ratings of dementia indicators were correlated to both functional and structural imaging. The strongest correlations (p<.05, corrected for multiple comparisons) included the combination of higher GMR and decreased GM volume in parts of the temporal cortex, including the parahippocampus/hippocampus, in the thalamus, caudate, and frontal lobe (BA 47). INTERPRETATION: The combination of increased GMR overlapping with less gray matter in these areas may be consistent with a compensatory brain response to an early stage of the disease process.