The Search for Environmental Influences on Autism Risk Expands at IMFAR 2010 by Alycia Halladay, Ph.D. Dr. Halladay is Autism Speaks' Director, Research for Enivronmental Services. As the emphasis on a role for environmental factors in autism continued to grow at this year's International Meeting for Autism Research (IMFAR), so did the list of candidate environmental risk factors under study. Among the many factors discussed at the meeting were hazardous air pollutants, assisted reproductive technologies, medications given during pregnancy and childbirth, maternal infections, smoking, nutritional factors, maternal stress, and chemicals such as flame retardants.
. Several studies presented by researchers at the latest International Meeting for Autism Research (IMFAR) suggested that a variety of environmental factors likely contribute to the risk of developing autism. This year, as the emphasis on the role for environmental factors in autism continued to grow, so did the list of candidate environmental risk factors under study. Among the many factors discussed at the meeting were hazardous air pollutants, assisted reproductive technologies, medications given during pregnancy and childbirth, maternal infections, smoking, nutritional factors, maternal stress, and chemicals such as flame retardants. Many of the projects were funded by Autism Speaks or Autism Speaks-funded researchers, including those leading the Early Autism Risk Longitudinal Investigation (EARLI) study and the International Collaboration for Autism Registry Epidemiology.
Epidemiological data presented at IMFAR 2010 supported a link to autism for some environmental factors while ruling out a link for others. Two of the exposures found to be associated with autism were gestational diabetes in pregnancy and medical interventions related to assisted reproductive technology, specifically ovulation induction or in vitro fertilization. Other exposures, such as smoking, prenatal stress, and hazardous air pollutants in Southern California were not found to be associated with an increased risk for autism or differences in autism severity. Many of the findings presented by researchers were considered preliminary and will require replication with larger samples.
Not all risk factors will impact everyone equally, and researchers at the conference found that the effects of some early environmental exposures, such as maternal infection during pregnancy, were dependent on the particular individuals being exposed. For example, maternal bacterial infection during pregnancy was more likely to increase risk for autism when the infant was born prematurely or have low birth weight infants. Additional “high risk” groups may include children who spent time in neonatal care units as infants either due to low birth weight or gestational age. Further research needs to be carried out to validate and extend these findings, helping to better identify particularly susceptible – or perhaps even protected – subgroups. Moreover, although these epidemiological studies have found a link between these specific factors and autism risk, beyond replication of the data it will be important to address the biological mechanisms through which the candidate environmental factors are operating, including the role of genetic variation in vulnerability to specific environmental factors. As one example, using samples available through Autism Speaks' genetic data base, AGRE, researchers found variations in the sequences for genes related to the oxidative stress response. These gene mutations may impact the ability of a person to metabolize toxins.
To hasten discovery of environmental risk factors through epidemiological studies, Autism Speaks partnered with the National Institute of Environmental Health Sciences to facilitate the creation of a network of over 35 researchers involved in a dozen studies that collect biosamples and other data related to gene / environment interactions in ASD. It is hoped that the establishment of a network of researchers with common goals, challenges and needs, will facilitate advances in this field through collaborative efforts that could provide larger data sets. Researchers in the new network met together for the first time at this year's IMFAR. “We are thrilled to be partnering with the National Institute of Environmental Health Science to promote collaboration among epidemiologists studying environmental risk factors for autism,” commented Autism Speaks' Chief Science Officer, Geri Dawson, Ph.D. “We hope this new collaborative effort will help us identify strategies for accelerating research on environmental factors, what are the needed tools and gaps, and what are the most important questions we should be addressing.” For more on this network, read Dr. Geri Dawson's summary of IMFAR.
One specific environmental factor that was particularly highlighted among the IMFAR presentations this year was BDE-47, a chemical in the class of poly-brominated diphenyl ethers, or PBDEs, which are flame retardants used in plastics and consumer electronics. Scientists reported that peripheral blood cells treated with BDE-47 show an increased production of a cytokine called IL-6, which has previously been linked to autism-like behaviors in mice. Following up on this study, researchers from the same institution found behavioral deficits were induced by pre- and post- natal exposure to BDE-47, including spatial learning and perseverative behaviors. Another study at the conference focused on the interaction between exposure to BDE-47 and certain genetic risk factors, finding that deficits caused by BDE-47 were more severe in the presence of a mutation that effected expression of MeCP2, the gene that causes Rett Syndrome, a neurodevelopmental disorder related to autism. Finally, although an epidemiological study did not find increased levels of BDE-47 in children that had already been diagnosed with autism, a follow-up study using a prospective design to study “at-risk” infants is underway to determine possible critical windows of exposure during development. Therefore, in the case of BDE-47, the neurobiological mechanisms of action are in the process of being identified. However, further epidemiological research is needed to determine if this exposure is specifically associated with an outcome of autism.
While these findings are interesting, how do scientists convey important research findings related to risk for autism when there is still uncertainty regarding their meaning for individual families affected by autism? This was the topic of a special IMFAR symposium this year titled “Ethics of Communicating Scientific Risk,” led by Craig Newschaffer, Ph.D. and Michael Yudell, Ph.D. from Drexel University. Families rely on scientific research to establish the credibility and reliability of findings, and on advice from professionals regarding whether and how they should change their behavior to modify risk. Discussions at the symposium centered around making sure to keep in mind the prevalence of the risk factor in the general population – how common it is – and whether the benefits of exposure outweigh the risks. Because families primarily seek information from autism care providers, such experts should be receiving training on how to evaluate findings and communicate them effectively. Overall, this symposium and the discussions to follow will provide a framework for scientists, clinicians, autism providers and the media to more effectively convey information in an ethical and responsible way.
Find more information about the broad range of environmental exposures being studied through Autism Speaks support.