MRI volumes of the hippocampus and amygdala in adults with Down's syndromewith and without dementia

Objective: This study sought to determine whether volumes of the hippocampu s and amygdala are disproportionately smaller in subjects with Down's syndr ome than in normal comparison subjects and whether volume reduction is grea ter in Down's syndrome subjects with dementia. Method: The subjects were 25 adults with Down's syndrome (eight with dementia) and 25 cognitively norma l adults who were individually matched on age, sex, and race. Magnetic reso nance imaging measures included volumes of the hippocampus, amygdala, and t otal brain. Nineteen of the Down's syndrome subjects had follow-up scans (i nterscan interval=9-41 months). Results: Nondemented Down's syndrome subjec ts had significantly smaller volumes of the hippocampus, but not the amygda la, than their comparison subjects, even when total brain volume was contro lled for. Volumes of both the hippocampus and the amygdala were smaller in the demented Down's syndrome subjects than in their comparison subjects, ev en when total brain volume was controlled for. Age was not correlated with volume of the hippocampus or amygdala among the nondemented Down's syndrome subjects and the comparison subjects; age was correlated with volume of th e amygdala, but not the hippocampus, among the Down's syndrome subjects wit h dementia. Changes in volume over time were not statistically significant for either the demented or the nondemented subjects. Conclusions: Hippocamp al volume, while disproportionately small for brain size in individuals wit h Down's syndrome, remains fairly constant through the fifth decade of life in those without dementia. All subjects over age 50 who had Down's syndrom e demonstrated volume reduction in the hippocampus as well as clinical sign s of dementia. Dementia was also associated with volume reductions in the a mygdala that exceeded reductions in total brain volume.