(RxWiki News) Autism is a developmental condition that has been separately linked to both genetic and environmental factors. Recent research shows how it's possible that both factors can work together.
A recent study found that the risk of autism was increased by high levels of exposure to certain types of air pollution, and that genetics alone did not increase the risk.
The researchers believe that the risk was associated with a specific interaction between the baby's genes and the mother's history of environmental exposure to various air pollutants.
"Discuss past environmental exposures with your doctor if you are pregnant."
The lead author of this study was Heather E. Volk, MPH, PhD, from the Department of Preventive Medicine of the Keck School of Medicine, the Department of Pediatrics of the Children's Hospital Los Angeles and the Zilkha Neurogenetic Insitute in the Keck School of Medicine--all part of the University of Southern California in Los Angeles, California.
The researchers used participant data from a previous study called the Childhood Autism Risks From Genetics and the Environment Study.
The current study used 251 young children between the ages of two and five years old. All of these participants had a confirmed diagnosis of autism or an autism spectrum disorder.
The participants were all born in California and had at least one biological parent that spoke either English or Spanish.
The study also included 156 children who had typical development as study controls.
The researchers first interviewed all the participants' parents on demographic data (age, race, etc.), medical history and potential environmental exposures.
The participants' mothers were asked to provide a detailed residential history, including every address the mother had lived at from birth to the present. The researchers also asked the mothers to report if the participant had lived somewhere not included in the mother's history.
The researchers then used the residential data to determine average pollution exposure for each participant based on the geographical surroundings of each residence. Next, blood samples were collected from all the participants so the researchers could look for a certain gene in the participants’ DNA called the MET genotype.
The researchers considered potential factors such as the sex of the participant, the ethnicity of the participant, the highest level of education in each household, the mother's age, whether or not a participant's family owned or had previously owned a house and whether or not the mother smoked cigarettes during pregnancy.
The MET CC gene was compared against the MET CG/GG genes because previous studies have linked autism to people with the CC variant of the MET gene.
The researchers found that the participants with the MET CC gene were less likely to have had their mother smoke during pregnancy and less likely to have suffered high levels of nitrogen dioxide exposure than the participants with the CG or GG gene.
The findings also revealed that the participants with the MET CC gene did not have an increased risk of autism compared to the participants with the CG or GG genes.
The participants who were in the top quartile for traffic-related air pollution were found to have 1.7 times greater odds of having autism. In addition, the top quartile of large particle and small particle exposures were associated with 2.5 times and 1.9 times greater odds of having autism.
Lastly, the participants in the top quartile of nitrogen dioxide exposure had 1.7 times greater odds of having autism.
The researchers then found that the participants with the CC gene who were in the top quartile of exposure to traffic-related pollution had 2.9 times greater odds of having autism.
The researchers concluded that the participants with the MET CC gene who had high levels of exposure to air pollutants were at higher risk for autism compared to the participants with the CG or GG gene and low levels of exposure.
In addition, the findings showed that the MET CC gene did not affect 75 percent of the participants who experienced low levels of exposure; therefore, the researchers suggested that the risk of autism is connected to the combination of genetics and environmental exposures.
More research is needed to understand the details of the biology behind this connection.
This study was published in the January 2014 edition of Epidemiology.
The National Institute of Environmental Health Sciences and the UC Davis MIND Institute provided funding.