Dr. Hempstead and her colleagues propose that the signaling peptide brain-derived neurotrophic factor (BDNF) may be over expressed in the brains of children with autism, causing neurological defects that lead to the disorder. BDNF is a regulator of brain growth, and children with the disorder tend to have abnormally large brains during early development. Hempstead and colleagues have preliminary evidence that both neurons and blood platelets regulate BDNF expression with the same mechanism, suggesting that people who produce high levels in one tissue are also likely to have high levels in the other. To test their hypothesis, the researchers first plan to determine the neurological consequences of expressing too much BDNF — both unprocessed and mature — in specific regions of the mouse brain known to develop abnormally in autism. The researchers then plan to assess whether BDNF over expression affects the social and cognitive behaviors of these mice. The researchers also aim to uncover the cause of high blood levels of BDNF in children with autism. Hempstead and colleagues plan to assess the steps of BDNF synthesis and processing as well as the turnover of the peptide from the bloodstream in blood samples from affected children in order to find which steps are deregulated in children with autism.