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Scientists figure out cause for Down's Syndrome

Scientists have shown that inheritance of an extra chromosome in Down's syndrome that leads to decreased protein production is responsible for impaired cognitive functions, says a study. Researchers have discovered that the extra chromosome inherited in Down syndrome impairs learning and memory because it leads to low levels of SNX27 protein in the brain. What is it about the extra chromosome inherited in Down syndrome -- chromosome 21 -- that alters brain and body development? Researchers at Sanford-Burnham Medical Research Institute (Sanford-Burnham) have new evidence that points to a protein called sorting nexin 27, or SNX27.

SNX27 production is inhibited by a molecule encoded on chromosome 21. The study, published March 24 in Nature Medicine, shows that SNX27 is reduced in human Down syndrome brains. The extra copy of chromosome 21 means a person with Down syndrome produces less SNX27 protein, which in turn disrupts brain function. What's more, the researchers showed that restoring SNX27 in Down syndrome mice improves cognitive function and behavior, reports Science Daily.

'In the brain, SNX27 keeps certain receptors on the cell surface receptors that are necessary for neurons to fire properly,' said Huaxi Xu, Ph.D., professor in Sanford-Burnham's Del E. Webb Neuroscience, Aging and Stem Cell Research Centre and senior author of the study. 'So, in Down syndrome, we believe lack of SNX27 is at least partly to blame for developmental and cognitive defects.'

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What is Down's Syndrome?

Down syndrome or trisomy 21 (also Down's syndrome) is a genetic disorder caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British doctor who first described it in 1866. The condition is characterized by a combination of major and minor differences in body structure. Often Down syndrome is associated with some impairment of cognitive ability and physical growth as well as facial appearance. Down syndrome is usually identified at birth. Check out the symptoms of Down's syndrome.

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