Could prenatal plastic exposure trigger autism in boys?

Florey scientists have found evidence of plastic, commonly used in food packaging, in pregnant women who gave birth to sons with autism.

Published in Nature Communications, the study reported higher levels of bisphenol A (BPA) in urine samples taken from these women, supporting the hypothesis of a possible link between autism and exposure to plastic chemicals in the womb.

The team, led by Dr Wah Chin Boon and Professor Anne-Louise Ponsonby, analysed two large birth cohorts — the Barwon Infant Study (BIS) in Australia and the Columbia Centre for Children’s Health and Environment in the USA.

The study examined children with lower levels of the enzyme aromatase, which in the brain converts testosterone to neuroestrogen, Ponsonby said.

The link between BPA presence and autism was particularly evident in the top fifth of boys with vulnerability to the endocrine-disrupting properties of this chemical. That is, those with lower levels of the enzyme aromatase.

BPA levels in pregnancy and autism symptoms

The study found boys in that group, who were born to mothers with higher urinary BPA levels in late pregnancy, were 3.5 times more likely to have autism symptoms by age two years; were six times more likely to have a verified autism diagnosis by age 11 years than those whose mothers had lower levels of BPA during pregnancy. In both birth cohorts, mechanistic evidence demonstrated higher BPA levels were associated with epigenetic (gene switching) suppression of the aromatase enzyme overall.

“Our work is important because it demonstrates one of the biological mechanisms potentially involved. BPA can disrupt hormone controlled male foetal brain development in several ways, including silencing a key enzyme, aromatase, that controls neurohormones and is especially important in foetal male brain development. This appears to be part of the autism puzzle,” Ponsonby said.

Ponsonby said BPA, similar bisphenols and other plastic chemicals with endocrine-disrupting effects are now widespread and almost impossible for individuals to avoid.

“We all ingest plastic chemicals in many ways — through ingesting plastic food and drink packaging, inhaling home renovation fumes and through the skin from sources such as cosmetics. There are so many ways these chemicals enter our bodies, so it’s not surprising that BPA was present in a large proportion of the women’s urine samples we studied. It’s important for us to understand how these plastics affect our health,” Ponsonby said.

These findings are now feeding into public safety regulators which update safety recommendations on manufactured chemical exposure, including plastic chemicals, during pregnancy and early life.

The team also looked for ways to reduce the adverse effect of BPA on the aromatase system. “10-hydroxy-2-decenoic acid shows early indications of potential in activating opposing biological pathways to improve autism-like characteristics when administered to animals that have been prenatally exposed to BPA. It warrants further studies to see whether this potential treatment could be realised in humans,” Wah Chin Boon said.

A ‘rogue’ hormone?

Many studies have shown associations between the presence of BPA and a range of abnormal developments. ‘Association’ cannot automatically be assumed to be ‘causation’ but many scientists are working on this question, said Professor Ian Rae from the School of Chemistry at the University of Melbourne.

“Suspicions about its toxic effects are strong, but the effects are usually weak and hard to detect, requiring extensive population studies, so it has proved extremely difficult to see exactly how BPA exerts its effects — something that’s need to link cause and effect,” said Rae, who was also an advisor to the United Nations Environment Programme on chemicals in the environment and is former President of the Royal Australian Chemical Institute.

“The researchers who did the work reported in this paper found an association between higher BPA blood levels and the development of autism spectrum disorders in male children. What’s really new about their results is that they were able to pin the effect to a biological pathway that is important in brain development. In other words, BPA is acting as a ‘rogue’ hormone to out-compete the natural hormone that is usually involved in this pathway.

The case is compelling, they write, and supports broader evidence on the need to further reduce BPA exposure, especially in pregnancy. In addition to locating the pathway of BPA action, they have found in laboratory studies that an unusual fatty acid (10HDA to avoid a difficultly long name!) competes with BPA and can be administered to alleviate its effects.

Further research needed

This is interesting research worthy of further investigation but it’s important to understand there are many other genetic variations that are possible contributors to autism that have similar amounts of evidence, said Dr Elisa Hill-Yardin, a joint ARC Future Fellow and Senior Vice Chancellor’s Research Fellow at RMIT University in Melbourne and leader of the Gut-brain Axis Laboratory.

“Ultimately we still don’t know for sure what causes autism for most people and a normal healthy diet and lifestyle advice should be followed during pregnancy.

“Future work to carefully measure bisphenol A levels over time during pregnancy to clarify these findings as well as further assessing the effects of the 10HDA fatty acid will be informative. The effects of diet may also be important in these findings.”

Image credit: iStock.com/mmpile