This week’s “Got Questions?” answer comes from Alycia Halladay, PhD, Autism Speaks director of research for environmental sciences. [Editor's note: Dr. Halladay is now the chief science officer at the Autism Science Foundation.]
If you’ve been following autism research in recent years, you have probably read—many times—that familial, or inherited, risk is seldom the whole picture. A few inherited genes are sufficient by themselves to cause autism. But most so-called “autism genes” only increase the risk that an infant will go on to develop this developmental disorder. As is the case in many complex diseases, it appears that autism often results from a combination of genetic susceptibility and environmental triggers.
This is where epigenetics comes in. Epigenetics is the study of the factors that control gene expression, and this control is mediated by chemicals that surround a gene’s DNA. Environmental epigenetics looks at how outside influences modify these epigenetic chemicals, or “markers,” and so affect genetic activity.
It is important to remember that scientists use the term “environment” to refer to much more than pollutants and other chemical exposures. Researchers use this term to refer to pretty much any influence beyond genetic mutation. Parental age at time of conception, for example, is an environmental influence associated with increased risk of autism, as are birth complications that involve oxygen deprivation to an infant’s brain.
Because epigenetics gives us a way to look at the interaction between genes and environment, it holds great potential for identifying ways to prevent or reduce the risk of autism. It may also help us develop medicines and other interventions that can target disabling symptoms. We have written about epigenetics previously on this blog (here and here). So in this answer, I’d like to focus on the progress reported at a recent meeting hosted by Autism Speaks.
The Environmental Epigenetics of Autism Spectrum Disorders symposium, held in Washington, D.C. on Dec. 8, was the first of its kind. The meeting brought together more than 30 leaders in autism neurobiology, genetics and epidemiology with investigators in the epigenetics of other complex disorders to promote cross-disciplinary collaborations and identify opportunities for future studies.
Rob Waterland, of Baylor College of Medicine in Texas, described epidemiological studies and animal research that suggested how maternal nutrition during pregnancy can affect epigenetic markers in the brain cells of offspring.
Julie Herbstman, of Columbia University, described research that associated epigenetic changes in umbilical cord blood with a mother’s exposure to air pollutants known as polycyclic aromatic hydrocarbons (PAHs). PAHs are already infamous for their association with cancer and heart disease.
Rosanna Weksberg, of the Hospital for Sick Kids in Toronto, discussed findings that suggest how assisted reproductive technology may lead to changes in epigenetically regulated gene expression. This was of particular interest because assisted reproduction has been associated with ASD. Taking this one step further, Michael Skinner, of Washington State University, discussed “transgenerational epigenetic disease” and described research suggesting that exposures during pregnancy produce epigenetic changes that are then inherited through subsequent generations.
Arthur Beaudet, of Baylor College of Medicine, discussed a gene mutation that controls availability of the amino acid carnitine. This genetic mutation has been found to be more prevalent among children with ASD than among non-affected children, suggesting that it might be related to some subtypes of autism. Further study is needed to follow up on the suggestion that dietary supplementation of carnitine might help individuals with ASD who have this mutation. Caution is needed, however. As Laura Schaevitz, of Tufts University in Massachusetts, pointed out, studies with animal models of autism suggest that dietary supplementation may produce only temporary improvements in symptoms of neurodevelopmental disorders.
So what does this all mean for research that aims to help those currently struggling with autism? The meeting participants agreed that the role of epigenetics in ASD holds great promise but remains understudied and insufficiently understood. For clearer answers, they called for more research examining epigenetic changes in brain tissues. This type of research depends on bequeathed postmortem brain tissue, and Autism Speaks Autism Tissue Program is one of the field’s most important repositories. (Find more information on becoming an ATP family here).
The field also needs large epidemiological studies looking at epigenetic markers in blood samples taken over the course of a lifetime. One such study is the Early Autism Risk Longitudinal Investigation (EARLI). More information on participating in EARLI can be found here.
Autism Speaks remains committed to supporting and guiding environmental epigenetics as a highly important area of research. We look forward to reporting further results in the coming year and years.
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Read more autism research news and perspective on the science page.