Learning Disability Today
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Protein linked to cognitive impairment in people with Down’s syndrome

The lack of a certain protein in the brains of people with Down’s syndrome could be a cause of learning and memory problems, according to a US study.

Researchers in Florida found new evidence that a molecule encoded in the extra chromosome inherited in Down’s syndrome—chromosome 21—inhibits the production of a protein called sorting nexin 27, (SNX27), which in turn disrupts function in the brains of people with Down’s syndrome.

But the study, published in the journal Nature Medicine, showed that restoring SNX27 in mice with Down’s syndrome improved cognitive function and behaviour.

In tests on mice, the researchers found that SNX27 helps keep glutamate receptors on the cell surface in neurons. Neurons need glutamate receptors in order to function correctly. With less SNX27, these mice had fewer active glutamate receptors and thus impaired learning and memory.

“In the brain, SNX27 keeps certain receptors on the cell surface—receptors that are necessary for neurons to fire properly,” said professor Huaxi Xu from Sanford-Burnham Medical Research Institute in Florida 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.”

Xin Wang, a graduate student in Xu’s lab and first author of the study, added:  “Everything goes back to normal after SNX27 treatment. It’s amazing—first we see the glutamate receptors come back, then memory deficit is repaired in our Down syndrome mice. Gene therapy of this sort hasn’t really panned out in humans, however. So we’re now screening small molecules to look for some that might increase SNX27 production or function in the brain.”

The BBC reported that Carol Boys, chief executive of the Down’s Syndrome Association, said the findings were interesting, but emphasised therapeutic treatments that might lead to improvement to cognition in people with Down’s syndrome are still a long way away.

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