The morphological features of the cerebral hemispheres of nine subjects with Williams syndrome (WS) and six with Down syndrome (DS) have been compared using MRIs at the University of California at San Diego, La Jolla, CA. Ages ranged from 10 to 20 years (mean, 15 years). Total cerebral gray matter and total cerebral volume were reduced in both retarded groups when compared to normal controls. Regional analysis of gray matter showed significant differences between WS and DS: frontal cortex and limbic structures of the temporal lobe are disproportionately reduced while the thalamus, putamen, and globus pallidus are normal in volume in DS. Frontal and temporal limbic structures are relatively preserved in WS. 
COMMENT. Previous studies in this laboratory showed cerebellar changes in these syndromes: total cerebellar size was reduced in DS and normal in WS. Regional analysis of the cerebellum of WS subjects showed a small vermis and enlarged hemispheres. The relative sparing of frontal and cerebellar structures in WS may explain the relative fluency of speech in subjects with this syndrome. Poor development of cerebellar, limbic, and frontal structures in subjects with DS correlate with their language and social-affective disabilities.
A relationship between Down syndrome and Lewy bodies, a major neuropathological feature of Parkinson’s disease, is reported in two middle-aged patients examined at the Department of Neuropathology, Newcastle-upon-Tyne, UK . The substantia nigra was normal in size while the locus coeruleus was small. Alzheimer-type pathology was also present. An etiological connection between Parkinson’s and Alzheimer’s diseases and trisomy 21 was suggested.