Neuroanatomy of Down's syndrome: A high-resolution MRI study

Objective: Down's syndrome, the most common genetic cause of mental retarda tion, results in characteristic physical and neuropsychological findings, i ncluding mental retardation and deficits in language and memory. This study was undertaken to confirm previously reported abnormalities of regional br ain volumes in Down's syndrome by using high-resolution magnetic resonance imaging (MRI), determine whether these volumetric abnormalities are present from childhood, and consider the relationship between neuroanatomic abnorm alities and the cognitive profile of Down's syndrome. Method: Sixteen children and young adults, with Down's syndrome (age range= 5-23 years) were matched for age and gender with 15 normal comparison subje cts. High-resolution MRI scans were quantitatively analyzed for measures of overall and regional brain volumes and by tissue composition. Results: Consistent with prior imaging studies, subjects with Down's syndro me had smaller overall brain volumes, with disproportionately smaller cereb ellar volumes and relatively larger subcortical gray matter volumes. Also n oted was relative preservation of parietal lobe gray and temporal lobe whit e matter in subjects with Down's syndrome versus comparison subjects. No ab normalities in pattern of brain asymmetry were noted in Down's syndrome sub jects. Conclusions: The results largely confirm findings of previous studies with respect to overall patterns of brain volumes in Down's syndrome and also pr ovide new evidence for abnormal volumes of specific regional tissue compone nts. The presence of these abnormalities from an early age suggests that fe tal or early postnatal developmental differences may underlie the observed pattern of neuroanatomic abnormalities and contribute to the specific cogni tive and developmental deficits seen in individuals with Down's syndrome.