Lead researcher Huaxi Xu started to unravel this mystery a few years back when he and his colleagues began examining the function of a brain cell protein called sorting nexin 27 (SNX27). Mice that were missing the gene for this protein were found to present similar brain characteristics to individuals with Down’s syndrome, and humans with this condition presented depleted SNX27 levels Further digging revealed that this protein is necessary for the maintenance of a crucial cell surface receptor that is necessary for neurons to communicate. Without SNX27, neuronal activity is reduced and thus learning and memory is compromised.