Autism spectrum disorder (ASD) has increased in frequency over the years. Some of that is due to better diagnosis. Some of that has been due to reclassifying children with other developmental disabilities as having ASD.
However, that does not account totally for the increase. A variety of things have been suggested as potential causes over the years.
There is a new theory that has gained some traction over the last few years. In 2016 a study came up with a hypothesis that nitrous oxide and nitrogen dioxide might be associated with autism. Both of these are pollutants that come from vehicle emissions and the combustion of industrial fuels.
Clearly the amount of these in the atmosphere continues to increase so it would be consistent with an increase in ASD.
After that a study using a mouse model looked at the effects of nitrous oxide on genes during pregnancy. This showed that nitrous oxide could produce genetic damage.
Then in 2019 a study in the Journal of the American Medical Association looked at 132,256 births. That study suggested that there was an association between exposure to nitrous oxide and autism.
In June 2023 another study from Israel found the same likely association. In that study they took stem cells from autistic patients. They exposed those cells to chemicals that reduce nitrous oxide and saw positive changes. The problem was that the study did not have many patients.
In November 2024 a study looked at pollutants in general for a relationship to autism. Pollutants in general affect developing brain cells. Things like particulate matter, ozone and sulfur dioxide produce changes. For example, particulate matter can alter hormone levels in the brain.
Nitrous oxide and nitrogen dioxide activate genes in the brain that cause increased inflammation. Disruption of these genes do not change the DNA. However, they do interfere with how the DNA functions. The chemicals that the brain puts out are altered. Altered chemicals are often found in patients with autism.
The conclusion of the article was that air pollution is a significant environmental risk factor for ASD. Exposure to the various pollutants during pregnancy and early childhood increase the risk for ASD.
As we continue to gather information, the next steps might include seeing if there is a way of altering the symptoms using chemicals that reduce nitrous oxide (like the June 2023 study). This might lead to a new way of treatment.