Down Syndrome (Trisomy 21)
What is Down Syndrome?
Down Syndrome (DS) is the most common genetic cause of developmental disability currently known. DS is caused by an extra copy of chromosome 21 (Trisomy 21), and is manifested by microcephaly and varying degrees of mental retardation. Compared with IQ-matched controls without DS, individuals with DS have particular problems with language, short term memory, and with changing tasks.
People with DS have a very high incidence of early onset of clinical and neuropathological symptoms associated with Alzheimer disease. Previous structural brain imaging studies have shown that the frontal lobes and cerebellum are disproportionately small in adults with DS. The parietal lobes and the sub-cortical region known as the basal ganglia have been shown to be relatively spared in DS.
Our laboratory is currently analyzing both the structure and function of children with DS. Our ongoing structural imaging work is examining the relative size and tissue proportions of different brain regions between people with and without DS.
Our preliminary findings suggest that people with DS have decreases in the volume of gray and white matter in the frontal lobes and cerebellum. These findings are interesting since the frontal lobes are thought to perform roles in language and memory.
Structural MRI Studies in Down Syndrome
Consistent with prior imaging studies, subjects with Down's syndrome had smaller overall brain volumes, with disproportionately smaller cerebellar volumes and relatively larger subcortical gray matter volumes. In subjects with Down syndrome, there was a relative preservation of parietal lobe gray and temporal lobe white matter. The results largely confirm findings of previous studies with respect to overall patterns of brain volumes in Down's syndrome and also provide new evidence for abnormal volumes of specific regional tissue components. The presence of these abnormalities from an early age suggests that fetal or early postnatal developmental differences may underlie the observed pattern of neuroanatomic abnormalities and contribute to the specific cognitive and developmental deficits seen in individuals with Down's syndrome.
Further, our structural MRI analyses indicated that hippocampal volumes were significantly smaller in the Down syndrome group compared with age-matched normal controls, which may be primarily due to early developmental differences rather than neurodegenerative changes. In this study, amygdala volumes were not significantly different in subjects with Down syndrome.
For publications on this study click here.