During the 2008 presidential campaign, Alaska Governor Sarah Palin spoke about her son who had been born with Down syndrome. It brought attention to the genetic disorder that is triggered by a third copy of human chromosome 21 and is the most common cause of mental retardation in children. It leads to deficits in contextual learn and memory.
Down Syndrome Study
Now there is hope in a report because of a study done at Stanford University School of Medicine by Ahmad Salehi and his colleagues indicating that boosting levels of a neurotransmitter in the brain may reverse some of the cognitive abnormalities that characterize Down syndrome. It used an established mouse model of the condition, in which mice are engineered to have an extra, third copy of 104 genes on chromosome 16 that are homologous to genes on human chromosone 21.
Mice are known to show abnormal responses in behavioral tests for contextual learning. For example, they don't respond to fear conditioning, suggesting they can't learn to associate a shock with a tone. After first examining the brains of mutant mice, the researchers found a significant neurodegeneration in the brain area--- the locus coeruleus-- which produces and supplies other parts of the brain.
Human and Mice Brain Similarities
An interesting part of the study of the brain showed that the defect in the trisomy mice doesn't just effect humans with Down syndrome, it is also seen in individuals with Alzheimer's disease and other types of dementia. It is known that 25% or more people with Down syndrome go on to develop Alzheimer's type dementia. This is three to five times greater than that of the general human population. Trisomy 21 is defined as a naturally occurring genetic presence within the human community.
When the mice were injected with I-DOPS, a drug that can cross the blood-brain barrier and convert into norepinephrine, the mice significantly improved their performance in tests of both fear conditioning and nest-building, behaving more like normal animals. However, when the drug wore off, so too did the mutants' improved nest-building ability.
According to Salehi, "These results suggest that it may be possible to restore some cognitive function in Alzheimer's patients as well as Down syndrome sufferer using I-DOPS."
Hope for the Future of Down Syndrome
While this study presents some hope for the future, it is yet to be seen how this mouse model can be used in a clinical trial in humans. Meanwhile, Governor Palin's disclosure about having a Down syndrome child could mean that the general public has more understanding with fewer prejudicial profiles and more understanding about these members of the society.
Sources:
Science Translational Medicine
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