Posted by Alycia Halladay, Autism Speaks senior director for environmental and clinical research. Dr. Halladay and the rest of the Autism Speaks science staff are just back from four days of scientific sessions at the 2014 International Meeting for Autism Research (IMFAR), in Atlanta.
On Saturday, the last session at IMFAR included a panel of investigators who presented recent data on environmental epigenetics. You can read more about what epigenetics means and how it may influence autism risk here and here.
The study of epigenetics helps us understand how environmental influences can influence gene expression. By “environmental,” we mean not just environmental pollutants, but many kinds of nongenetic influences from parental age to prenatal stress inflammation.
Most of the studies that have looked at epigenetics have focused on a process called methylation. This is when chemicals called “methyl” groups turn on and turn off gene expression by attaching to crucial parts of the gene’s DNA.
By way of analogy, scientists compare methylation to a faucet. Turning on the faucet pours out methyl groups that attach to the DNA code. Turning off the faucet slows down the methyl groups that can attach to the DNA. Exposure to environmental factors can affect the “rate of flow” so to speak, or even how fast the “sink” of methyl groups drains. This can affect gene expression.
This special session at this year’s IMFAR grew out of a meeting that Autism Speaks co-organized with the Escher Fund for Autism last year. (Read more about that meeting – and view its videotaped presentations – here.)
Saturday’s presenters included M. Danielle Fallin, recipient of Autism Speaks’ first Philip and Faith Geier Autism Research Grant in Environmental Sciences. (Read about this research project here.) Dr. Fallin chairs the department of mental health at the Johns Hopkins Bloomberg School of Public Health. Also on the panel were Autism Speaks-funded researchers Christine Ladd-Acosta (also from Johns Hopkins), Janine LaSalle (UC Davis) and Jennifer Wolstenholme (University of Virginia). David Amaral from UC Davis served as discussant.
Some presenters indicated that epigenetic signatures may provide indirect biomarkers of exposures that can affect autism risk. Their research found that the specific epigenetic profile seen in the umbilical cord blood of a newborn prenatally exposed to tobacco smoke was very similar to that of a 3 year old who had been exposed to smoking during prenatal development. This suggests that researchers can detect exposures that occur during prenatal development by looking at blood in the child years after birth. This would overcome a huge obstacle in environmental epidemiology by shedding light on a mother’s exposures during pregnancy even when her blood is not available for testing.
Another important point brought out by the presenters is the role of “old” exposures in studying autism. Changes in our environment over the past two decades may provide insight into why we’re seeing autism’s prevalence increase. However, we can’t limit our investigations only to changes across the last 20 years. For example, research suggests that a chemical group called PCBs, or polychlorinated biphenyls, significantly alters the expression of genes by way of epigenetics. Yet despite the fact that PCBs were outlawed in the 1980s, we still see high levels in individuals today. These types of exposures are just as relevant as those that occurred more recently.
To understand the wide range in which exposures can affect DNA expression, researchers are starting to expose animals to different chemicals and then look at the behavior of offspring several generations later. The “great grandchildren” of exposed mice show behavioral changes, yet they were never directly exposed to the chemical of interest. In humans, this multigenerational or transgenerational effect is seen after exposure to a drug called DES. (Learn more about the transgenerational effects of DES here.)
What’s happening here? The effects may ripple down to future generations through mutations in sperm and egg cells. We call this “germline exposures.” You can read more about the science behind germline exposures here.
In conclusion, epigenetics is a powerful way to understand how genes and environment interact with each other. Rather than looking at genes and environment separately, Autism Speaks is committed to understanding work in this area.
Learn more about the research projects we fund in the field of epigenetics here.