Extra chromosome inherited in Down syndrome-chromosome 21-alters brain and body development, a study has found.

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 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.

"In the brain, SNX27 keeps certain receptors on the cell surface-receptors that are necessary for neurons to fire properly," Huaxi Xu, Ph.D., professor in Sanford-Burnham`s Del E. Webb Neuroscience, Aging and Stem Cell Research Center and senior author of the study, said.

"So, in Down syndrome, we believe lack of SNX27 is at least partly to blame for developmental and cognitive defects," Xu said.

The study is published in the journal Nature Medicine.