Chemical messengers in the human body may play a significant role in the development of autism spectrum disorders (ASDs), according to a number of research presentations at the 27th International Neurotoxicology Conference, co-sponsored by Autism Speaks, in Research Triangle Park, North Carolina.
The chemical messengers called hormones regulate bodily functions such as growth, reproductive health and brain development. Understanding how hormones interact with genetic and environmental risk factors for autism will help scientists develop more focused treatments and interventions for people with ASDs, explains Alycia Hallady, Ph.D., Autism Speaks’ director of research for environmental science.
“No one is looking for a single cause of autism anymore,” Halladay says. “We’ve moved beyond just genes, and now we’re looking at interactions between genes and the environment, as well as different biological systems. It’s opening up doors for new avenues of research that could translate into new therapies.”
Researchers have long known that certain inherited genes contribute to ASDs. Many studies also show that the environment in which a fetus and infant matures can alter brain development and worsen the effects of these genes. In the case of autism, the clearest evidence of environmental influence surrounds early events such as conception, pregnancy and birth.
Researchers don’t yet fully understand the mechanisms by which exposure to certain chemicals and other environmental influences increase susceptibility to autism. But emerging evidence suggests that some alter levels of hormones that control brain development and normal brain function, according to several conference speakers.
For instance, work in mouse models of autism suggests that early social interactions can affect brain hormones involved in behaviors such as trust, empathy and eye contact, says conference co-chair Isaac Pessah, Ph.D., of University of California, Davis. It’s possible that even subtle changes in these hormones may increase the risk of ASD in those who are genetically predisposed to autism, and many persons with ASDs have lower levels of hormones associated with sociability, Pessah says.
Similarly, sickness during pregnancy may cause changes in hormone levels inside a mother’s placenta, which can affect fetal development, says speaker Paul Patterson, Ph.D., a professor at the California Institute of Technology. Patterson recently co-authored a study with Autism Speaks-funded graduate student Elaine Hsiao, showing that producing flu-like symptoms in pregnant mice both alters placental hormones and leads to autism-like behaviors in the resulting mouse pups.
The sex hormone testosterone, which regulates brain functioning and reproductive health in both men and women, may also play a role in ASDs. Some studies have linked autism to elevated levels of testosterone in a developing fetus, explains speaker Valerie Hu, Ph.D., a professor at George Washington University. Last year, she and her colleagues demonstrated that higher levels of testosterone (and lower levels of the sex hormone estrogen) can exacerbate the effects of at least one gene that may be associated with autism. Because testosterone is more abundant in males, this may partially explain why ASDs are four times more common in boys than girls, Hu says.
Hu and other speakers express hope that their research will lead to better treatments for ASDs. Because the causes of ASDs are complex and vary from person to person, “there’s not going to be a one-size-fits-all therapy,” Hu says. Importantly, she adds, a better understanding of the mechanisms behind that variation may help scientists design therapies tailored to different groups of people with ASDs.
In the meantime, many individuals and families affected by ASDs may benefit from following general public health guidelines such as eating foods rich in nutrients and antioxidants and avoiding exposure to pesticides and chemicals in plastics that are known to disrupt or mimic hormones, notes conference speaker Martha Herbert, M.D., of Harvard Medical School. “These aren’t treatments for autism,” Herbert admits, “but they can make a difference in people’s lives.”
--Report by Autism Speaks science writer Ariel Bleicher