Individuals with high levels of genetic variation and elevated exposure to a type of air pollution may be at an increased risk of developing autism, a new analysis shows.

The findings showed that environmental factors like exposure to air pollution (ozone, nitrogen oxide and particluate matter) contribute to the risk of autism.Genetic factors like copy-number variation -- deletions and duplications of repeated DNA -- also lead to the development of autism.According to the study, environmental factors like ozone, a harmful air pollutant at the ground level, can interact with genetic factors (copy number variation) to produce an even higher risk for autism than expected by adding the two risk factors, one that might not be found by studying the factors independently.This large effect could be the result of the fact that ozone is an oxidising agent and is known to produce reactive oxygen species, like peroxides, that cause cellular stress and can alter cell function in many ways. 

"Our research allows us for the first time to answer questions about how genetic and environmental risk factors for autism interact," said Scott B. Selleck, Professor at the Pennsylvania State University.High levels of copy-number variation may indicate a compromised state that is primed for the type of damage that ozone can cause, the researchers noted in the paper appearing in the journal Autism Research."This study showed the effect of a pollutant not previously associated with autism risk. This study may be one example of how taking genomic variation into account can help us identify new risk factors for autism," said Heather Volk, Assistant Professor at the Johns Hopkins Bloomberg School of Public Health.In the study, the researchers analysed 158 cases and 147 controls.