Autism has been the focus of much research and media attention over the past couple years ever since the false suggestion that the MMR vaccines cause autism. Luckily, there has been some good quality research recently that has begun to unravel the mechanisms behind autism and autism spectrum disorders (ASD). We know from previous research that autism does run in families and so must have a genetic component and scientists have been able to identify some of the genes that may be involved but it has been difficult to pin down what exposures may lead to the development of ASD in children who are already genetically susceptible. A new study published by researchers in the Journal of Environmental Health Perspectives suggests that exposure to particulate matter in air pollution may be partly to blame.
The study looked at children born between 1990 and 2002 that developed ASD and compared them to those children that did not. The researchers used a model of air pollution to predict the level of pollution that the mothers were exposed to before, during and after their pregnancy and related that to a diagnosis of ASD in the children. What they saw was that exposure to small particulate matter (about 2.5um in diameter) in air pollution was linked with and increase in the risk of developing autism especially when the exposure to the pollutants or particulate matter occurred within the last trimester. The researchers suggest that because particulate matter has been linked in the past with neurotoxic effects (damage to the brain) and damage to the fetus and that perhaps the particulate matter is affecting the brain development of the fetus. The results of this study agree with past studies where they saw that people who lived closer to a highway had greater risk of having a child with autism.
A word of clarification about the research; there has been much misunderstanding by media and the public about these results with people suggesting it is bogus because “I live right beside a factory/highway and my kids don’t have autism” or “If this is true then why doesn’t everyone in China have autism?” What you need to realize is that these results are not saying everyone exposed to air pollution will get autism. You probably know people who have smoked and not gotten cancer or COPD. It comes down to genetics. Someone needs to be susceptible to the disease and then be exposed to whatever helps trigger the disease. It’s also unlikely that air pollution is the only cause of autism. Autism is an umbrella term for a variety of disorders that all have similar symptoms or characteristics, similar to disorders like asthma and even cancer and there is no one cause for it. Instead people likely have a certain set of mutations in certain genes that makes them at risk for autism and then exposure to something during development pushes the scales one way. So this research showing that air pollution may lead to increased risk of developing autism doesn’t mean that everyone who is exposed to pollution will get autism. Instead you would need the right genetic abnormalities and environment exposures to develop autism.
Some things to note about the results, first the measure of air pollution exposure was done through modelling of historic levels and how close the mothers were to roads where pollution data was found. It would have been more comprehensive if they had measured the levels each mother was exposed to at their house and or work however, that would be costly. Secondly, the mothers moved around over the years and the exact date of their move wasn’t recorded and so the mother’s pollution exposure may have over or under estimated. The study was however designed well and used a large number of people over varying geographic locations meaning that the results are likely to be applicable to different populations.
This research and the ones before it have added to the growing picture of autism development and risk as well as the increasing evidence of pollution a damaging health effects. Pollution reduction efforts will go a long way to helping to limit the burden of chronic diseases and benefit everyone.