Brain Protein Linked To Down Syndrome May Be Cause Of Learning & Memory Problems


The Huffington Post  |  By Sara Gates

Posted: 03/26/2013 9:18 am EDT  |  Updated: 03/26/2013 12:47 pm EDT

It’s well-established that Down syndrome results when a person is born with an extra 21st chromosome, but so far, scientists haven’t pinned down what causes the condition’s symptoms.

New research, however, brings us one step closer to understanding Down Syndrome’s molecular biology.

Researchers at the Sanford-Burnham Medical Research Institute in California suggest that the cognitive and developmental problems associated with the syndrome are linked to a key brain protein.

The researchers came to this idea by studying mice that lacked one copy of the “SNX27” gene, which is responsible for encoding the protein of the same name. That protein helps keep neurons functioning properly, and the team found that a lack of SNX27 led to impaired learning and memory in the mice.

Seeing the similar characteristics between people with Down syndrome and SNX27-deficient mice, researchers hypothesized that a protein deficiency may contribute to symptoms associated with Down syndrome.

“In Down syndrome, we believe lack of SNX27 is at least partly to blame for developmental and cognitive defects,” Dr. Huaxi Xu, a Sanford-Burnham professor and lead author of the study, said in a statement.

But what brings about the loss of the SNX27 protein?

To further the research, Xu told The Huffington Post that his team plans to see if they “can identify any small molecule compounds that are able to down-regulate miR-155 or up-regulate the SNX27 protein.”
The answer may lie in a small RNA molecule called miR-155, which is encoded in the extra chromosome possessed by people with Down syndrome. The researchers found that an increase in miR-155 correlated with a decrease in the key protein.

“The disease is far more complicated than we can anticipate,” Xu said, “it involves so many genes, so many pathways.”

Although a cure may not be possible, Xu said he hopes that with further study of this specific mechanism, his team can find a way to “rescue the loss of learning and memory” associated with Down syndrome. He added, the research is still years away from human testing.

Sara Hart Weir, vice president of advocacy and affiliate relations for the National Down Syndrome Society, expressed her optimism with the researchers’ recent findings.

“The extra copy of chromosome 21 present in Down syndrome continues to teach scientists and researchers so much,” Weir told HuffPost. “We are excited to see if this study will lead to new ways to improve learning and memory in all individuals with Down syndrome.”

The research, entitled “Loss of sorting nexin 27 contributes to excitatory synaptic dysfunction by modulating glutamate receptor recycling in Down’s syndrome,” was published in the journal Nature Medicine on March 24.