Cerebral metabolic pattern in young adult Down's syndrome subjects: altered intercorrelations between regional rates of glucose utilization.

Correlations between regional cerebral metabolic rates for glucose, determined by positron emission tomography with [18F]-2-fluoro-2-deoxy-D-glucose, have been used to indicate functional associations between pairs of brain regions. This method was applied to data from 14 healthy adult subjects with trisomy 21 Down's syndrome (age less than 34 years) and from 24 age-matched healthy controls. Correlations were obtained between ratios of regional-to-global resting glucose utilization. In comparison to age-matched controls, the Down's syndrome group had many smaller correlations for region-pairs within and between the frontal and parietal lobes; some correlations were large and negative in the Down's syndrome group, but large and positive in the controls. One region so affected was the inferior frontal gyrus that includes Broca's area. This result is consistent with the relatively greater language impairment in Down's syndrome subjects. The thalamus also had smaller correlations with temporal and occipital regions in the Down's syndrome group compared to controls. These results suggest that Down's syndrome is accompanied by a functional disruption of neural circuits associated with directed attention.