September 24, 2021

I, Science

The science magazine of Imperial College

New findings suggest that the polluted air we breathe threatens our brain, Nicole Samuel explores.

smog imageRecent research suggests a link between air pollution and the risk of developing Autism Spectrum Disorders (ASDs). At present very little is known about ASDs and this research represents a large step forward in our understanding of the condition.

ASDs are a range of lifelong behavioural conditions that affect social interaction, awareness and communication. The effects vary between individuals, but can be extremely debilitating and some require a lifetime of support. Those with ASDs are also more likely to suffer from mental health conditions such as attention deficit hyperactive disorder (ADHD), anxiety and depression as well as learning difficulties.

Although the symptoms manifest themselves during infancy, it is believed that the causative process occurs during foetal brain development. The cause has yet to be defined – but both genetics and exposure to environmental agents play a role in the development of ASDs. Recent research suggests that air pollutants could represent a significant environmental risk.

Population based studies have shown that children exposed to fine particulate matter, such as released from vehicle engines, during early life are more likely to develop ASDs compared to unexposed counterparts. This association has been replicated across studies – however it is unclear if the timing of exposure has any significant effect. A study at the Harvard School of Public Health found that exposure during the third trimester of pregnancy carries a much higher risk than any other time. However others have shown a significant association with exposure during infancy. All studies do corroborate a connection between exposure and brain dysfunction that could lead to the development of ASDs.

The current hypothesis is that exposure during critical brain development in late pregnancy and early life could interfere with the normal pathway of growth. This could lead to lifelong changes in brain function that could contribute to ASDs.

Research at the University of Rochester Medical Centre, showed that mice exposed to airborne particulates during brain development had changes in brain structure consistent with those seen in autistic children. Additionally the changes seen were different in male and female mice. In females, the brain showed evidence of inflammation, which persisted throughout life. Inflammation, and the associated activation of the immune system have long been linked to the development of ASDs due to their impact on the structure and functioning of the cells within the brain. In male mice, there was enlargement of the lateral ventricles – a condition called ventriculomegaly, which is linked to behavioural changes in humans as well as ASDs and schizophrenia.

This research ties together air pollution and ASDs, but a causative relationship is far from proven. Further work is needed to clarify the risk and the interactions with genetic factors. However these findings are one piece of the puzzle and bring us that little bit closer to understanding, treating and preventing autism spectrum disorders.

Image: Wikimedia commons