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 have new evidence that points to the protein SNX27. SNX27 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. Restoring SNX27 in Down syndrome mice improves cognitive function and behavior.