Tune-in to NBC Nightly News this evening, February 17, at 6:30 p.m., ET, for an interview with Geri Dawson, Autism Speaks Chief Science Officer. Dawson will discuss the Autism Speaks funded Infant Brain Imaging Study (IBIS) reported online today in the American Journal of Psychiatry. The new study suggests the changes in brain development that underlie autism may be detectable in children as young as 6 months of age, even before symptoms emerge.
For more details, here’s a link to a Science news item on the study.
Today’s question came in response to my last blog post. In it, I explained that when scientists talk about the “environmental factors” that increase the risk of a disorder, they’re referring to pretty much any influence beyond genetics.
In the case of autism, the clearest evidence of environmental influence seems to surround very early events such as conception, pregnancy and birth. Those with the strongest link include parental age at time of conception (both mom and dad), maternal nutrition or illness during pregnancy, and certain birth complications.
The commenter’s question is a great one that scientists are actively exploring. The short answer is that inherited genes (DNA) and environmental factors seem to interact to influence whether an infant goes on to develop autism. So if the commenter’s twins are fraternal (meaning they share about half their DNA), the difference in their genetic makeup might explain why only one developed autism.
But what if the boys are identical twins–meaning they share exactly the same DNA? In this case, something beyond genes likely accounts for the different outcomes. Comparing the rates of autism among identical and fraternal twins provides clues.
In July, researchers used our Autism Genetic Resource Exchange (AGRE) to complete the largest autism twin study to date. They found a 70 percent overlap in autism among identical twins and a 35 percent overlap among fraternal twins. That overlap between fraternal twins is much higher than the estimated 19 percent overlap between different-age siblings.
These numbers tell us that it’s not always genes alone that determine whether a child develops autism. If it were, two identical twins would always share the same outcome, and the rate of a shared autism among fraternal twins would look more like that for different-age siblings. So we conclude that shared environmental influences are also at play.
Although twins share very similar pregnancy and birth environments, those environments aren’t exactly the same. For example, twins can have different positions in the womb or different placentas, and this can affect such environmental influences as blood and oxygen flow. Indeed, twins often have different birth weights, a known risk factor for autism.
It’s important to remember that “environmental” influences such as these don’t cause autism by themselves. Rather, if a child has a genetic predisposition for developing autism, these influences may further increase the risk.
Autism Speaks continues to fund and otherwise support research on both genetic and nongenetic risk factors for autism. EARLI is a network of researchers who follow mothers of children with autism beginning at the start of another pregnancy. IBIS is a study of early brain development in the younger siblings of children with autism. These studies depend on the participation and support of the autism community. Please visit our Participate in Research page to learn more.
Importantly, these studies provide insights into the underlying biology of different types of autism. This in turn becomes a basis for developing ways to treat and possibly prevent autism. As always, the goal of the research we support is to improve the lives of all on the autism spectrum.
And thanks for the question. Please keep them coming.
Last week, the Senate Environment and Public Works Committee convened a panel of experts to investigate the role of environmental factors in autism spectrum disorders (ASD; link to web archive for video). Although genetic factors are known to contribute to the risk of autism, we also need to understand environmental factors and their interactions with genetic susceptibility.
The dramatic increase in autism prevalence over the last two decades—over 600% during this period—underscores the need for more research on environmental factors. Our understanding of typical brain development combined with what we’ve learned from examining the brains of individuals with autism have focused efforts on the prenatal and early postnatal environment. To investigate environmental factors that may be active during this time, researchers are casting a wide net on potential environmental agents that can alter neurodevelopment, including exposure to metals, pesticides, polybrominated diphenylethers and other chemicals.
Isaac Pessah, Ph.D., Director of the University of California, Davis, Children’s Center for Environmental Health and Disease Prevention, participated in the panel and said in his testimony, “We must identify which environmental exposures and combination of exposures are contributing to increased overall risk in the population and identify the most susceptible groups. Only by bringing together the concerted effort of multidisciplinary teams of scientists can we identify which of the >80,000 commercially important chemicals currently in production promote developmental neurotoxicity consistent with the immunological and neurological impairments identified in individuals with idiopathic autism”.
To help speed an understanding of environmental factors, Autism Speaks is supporting research on several fronts. In 2008, Autism Speaks launched the Environmental Factors Initiative to fund investigators researching aspects of environmental causes and autism.
A collaboration with the National Institute for Environmental Health Sciences (NIEHS) has resulted in a network of 35 international scientists who gathered at this year’s International Meeting for Autism Research (IMFAR) to promote collaboration, identify gaps in our understanding and foster opportunities for innovative research which is discussed in more detail in Dr. Dawson’s 2010 IMFAR recap. This fall, Autism Speaks and NIEHS will co-sponsor a workshop to help identify the most promising strategies and scientific directions for understanding the role of the environment in ASD.
A large collaborative study which will pull together data from six international registries is being funded by Autism Speaks to explore early environmental risk factors for ASD.
Autism Speaks is also leveraging longstanding investments to make the best use of research resources that currently exist. For example, the Autism Genetic Resource Exchange (AGRE), a premiere genetic resource for scientists studying autism, is now collecting environmental data from families to pair with the genetic and medical data. Autism Speaks has partnered with the National Institutes of Health to fund the the EARLI and IBIS research networks to study environmental factors in infants at risk for autism. The EARLI network is following 1200 mothers of children with autism from the start of another pregnancy through the baby sibling’s third birthday. The IBIS network is charting the course of brain development in infant siblings of children with autism. Together with Autism Speaks, these groups are exploring both genetic and environmental risk factors for ASD.
Taken together, Autism Speaks’ investment in research on environmental factors promises to shed light on an important area of autism research that has until recently remained in the shadows. We look forwarding to following the new directions illuminated by the discoveries made possible by these various research opportunities.
In the 25 days leading up to Autism Speaks’ fifth anniversary, we summarized significant advances in autism science and updates since these advances occurred. This is a time for celebration and reflection, as well as focusing on next steps. On the eve of the fifth anniversary, this opinion piece, written by Nicholas Kristof, appeared in the New York Times and has generated considerable interest.
At Autism Speaks, we are investigating environmental links to autism as well as gene-environment interactions through our various grants and initiatives. In our environmental portfolio, we are currently supporting grants that examine the effects of environmental agents in animals, in which we look for some of the hallmarks of autism. Researchers in this area are studying animals with different genetic mutations and environmental exposures to the response of the immune system, the effectiveness of the body’s systems at clearing toxins and in changes in the expression of certain genes that occur as a result of the early environment. In addition we are also funding an expansion of epidemiology and brain development projects, including the Early Autism Risk Longitudinal Investigation (EARLI) and the Infant Brain Imaging Study (IBIS) to learn about gene-environment interactions that may affect the developing fetus. In the next weeks, we’ll be posting several pieces about gene-environment interactions to educate our community on these important interactions and inform you of the latest autism research in this area.