A new study linking air pollution to child autism suggests the condition may be triggered by environmental toxins. Researchers found that exposure to fumes from traffic and industrial sites increased the risk of a pregnant woman delivering an autistic child.
Autism is a brain development disorder that is believed to begin early on in pregnancy and manifests by three years of age, marked by social and communicative difficulties and repetitive physical behaviors. Because of variations in degrees of outward signs, the disorder was once divided into different types which have since merged under the umbrella of autism spectrum disorder (ASD). In the eight year period from 2000 to 2008, the number of children with ASD increased, from one in 150, to one in 88. Boys with ASD outnumber girls by almost five times.
Most research on ASD has focused on genetic factors. Studies have found that siblings of children with the dysfunction have a 25 times greater chance of being autistic than the general population. But the actual genetics of autism have been difficult to pin down. No specific gene mutation has been identified and it appears likely that a complex coexistence of factors come into play in the development of the pathology.
Because autism is believed to take root in the first trimester of pregnancy, and because geographic clusters of cases occur throughout the U.S., research is beginning to look at environmental factors. The first trimester is when the fetus is most susceptible to teratogens, which refer to substances that adversely affect fetal development. The oral intake of alcohol and medication can function as teratogens as well as environmental toxins absorbed by the mother by inhalation.
The study, published in PLOS Computational Biology, investigated insurance claims of 100 million people in the U.S., using genital malformation of boys as a gauge for parental exposure to environmental toxins. Genital abnormalities have a known epidemiological association with teratogens. The researchers found that, across the board, a one percent increase in genital malformations in boys was associated with a 283 percent increase in ASD, strongly suggestive of a link between environmental toxins and autism.
Although the study does not indict any specific substance as a direct determinant predictive of ASD, the sample size and results put it into the realm of groundbreaking, in that it shows that research on autism must now consider environmental as well as genetic factors. Lead investigator, Andry Rzhetsky a professor of genetic medicine at the University of Chicago, stated that the next step is determining which exposures matter.
Other studies have explored the environment connection with ASD. One such study, published a year ago in Environmental Health Perspectives, identified 7603 children with autism and, using 10 controls per subject, mapped the geographic locations of their birth addresses. These addresses where then linked to air monitoring stations in order to determine air pollution levels. The authors concluded that there was an association between cases of autism and air pollution levels, specifically those of traffic fumes.
The Rzhetsky study strongly suggests that future research on ASD widen their focus to include environmental factors as well as genetics. So far the most likely explanation for the genesis of autism is that genes for the disorder pre-exist, but their expression is linked to prenatal exposure to environmental toxins.
By Robert Wisnewski