Mutations in the important CNTNAP2 gene have been known to cause neuropsychiatric disorders in humans, but until now, scientists didn’t know why. According to a new Northwestern Medicine study, the answer may lie in abnormal synapses, the sites where communication between brain cells occurs.
In a recent paper published in Proceedings of the National Academy of Sciences, investigators analyzed neurons from mice without the protein that the CNTNAP2 encodes. They discovered that their synapses were smaller and weaker than usual.
“We also found that key molecules at synapses that help the cells talk to each other remained stuck inside the cells,” said senior author Peter Penzes, PhD, professor in Physiology and Psychiatry and Behavioral Sciences. “This was very unexpected because this type of abnormality has never been reported for a gene implicated in intellectual disability, autism, schizophrenia, language delay and epilepsy.”
When the gene functions properly, its protein, Caspr2, pushes molecules called AMPA glutamate receptors into the synapses, helping keep the sites large and healthy. But genetic mutations may result in less of the protein and, by extension, less of its value to the synapse.
Penzes and colleagues looked at both developing neurons and more mature neurons without the protein. Interestingly, the protein’s absence had no effect on the young cells; it led to synapse alterations only in the mature cells.
“Even though the gene is always in the body, the protein is expressed and required by the cell only later,” Penzes said. “This explains the late emergence of some of these disorders.”
Schizophrenia, for example, usually doesn’t manifest until adolescence or young adulthood.
“Overall these findings reveal new modalities whereby genes that cause psychiatric diseases may affect brain function,” Penzes said. “They may pave the way for future studies in human cells.”
This study was supported by National Institutes of Health (NIH) grants MH097216 and NS50220, Institute for Basic Science grant IBS-R002-D1 and German Research Foundation Research Fellowship SCHU2710/1-1.