Wednesday, 7 September 2016

On (banned) organochlorine compounds and autism risk

'Chemicals banned decades ago linked to increased autism risk today' went the press release attached to the findings reported by Kristen Lyall and colleagues [1] (open-access).

Observing that "higher levels of some organochlorine compounds during pregnancy are associated with ASD [autism spectrum disorder] and ID [intellectual disability]" the Lyall results once again push environmental factors back into the research spotlight. Indeed, environmental factors that were banned decades ago.

Including a cohort of children diagnosed with autism (n=545), those diagnosed with ID (also known at learning disability) (n-=181) and general population (asymptomatic?) controls (n=418) researchers accessed archived biological samples taken from mothers during the second trimester of pregnancy. Using some pretty sophisticated chemical analysis methods - "gas chromatography isotope dilution high resolution mass spectrometry (GCIDHRMS)" - various chemical compounds considered as POPs (persistent organic pollutants) were assayed for. Most if not all of these compounds were banned in the 1970s because of their potential effects on health. Because of their chemical nature however (i.e. enjoying bathing in fats) they can and do still persist in the environment, particularly in the food chain.

Results: various PCBs (polychlorinated biphenyl ethers) and "persistent pesticides" were included in the chemical analysis of maternal samples. Some, but not all, were reported in samples across the different groups. After some statistical wizardry in terms of adjusting samples and the results for various factors ("children with ASD were approximately four times as likely to be male than female... have older parents, and mothers with higher education") authors concluded that a few of the metabolites looked at might be linked to autism risk; specifically: "that exposure to PCB congeners in utero may influence risk of ASD in offspring."

"Primary analyses highlighted PCB 138/158 and PCB 153 in association with ASD, though other correlated congeners also demonstrated associations above the null." PCB 138/158 also seemed to show some sort of connection to the risk of offspring ID too "suggesting the impact of exposure to this congener on neurodevelopment broadly." Conversely, none of the other organochlorine compounds seemed to show any (significant) connection to autism offspring risk. Something similar has been talked about before with this broad collection of compounds in mind under more direct analysis conditions (see here). The authors conclude that further research is required to both substantiate their findings and also ascertain some of the hows and whys of these compounds in relation to autism and ID. Importantly, they acknowledge that their list of compounds tested may not be the whole story in terms of the 'multiple chemicals' people are exposed to over a lifetime.

These are rather interesting results. Not least because the potential legacy of these compounds continues years and years after production of them had all but ceased following health concerns. That researchers also focused on maternal pregnancy blood samples again (see here) puts gestational 'exposure' front and centre when it comes to potential effects and mechanisms too. The idea that immune function could be a target effect of such compounds when it comes to offspring autism risk is also explored by the authors: "effects on the immune system is another particularly likely mechanism." This would also seem to tally with the growing evidence that maternal immune function during the nine months that made us might be an important part of aetiology for at least some autism and/or more general neurodevelopmental issues.

The story continues as it might with other compounds too [2] on this 'TENDR' area of research...

To close, Worf don't like the lute...

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[1] Lyall K. et al. Polychlorinated Biphenyl and Organochlorine Pesticide Concentrations in Maternal Mid-Pregnancy Serum Samples: Association with Autism Spectrum Disorder and Intellectual Disability. Environ Health Perspect. 2016. Aug 23.

[2] Jeddi MZ. et al. The role of phthalate esters in autism development: A systematic review. Environ Res. 2016 Aug 24;151:493-504.

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ResearchBlogging.org Lyall K, Croen LA, Sjödin A, Yoshida CK, Zerbo O, Kharrazi M, & Windham GC (2016). Polychlorinated Biphenyl and Organochlorine Pesticide Concentrations in Maternal Mid-Pregnancy Serum Samples: Association with Autism Spectrum Disorder and Intellectual Disability. Environmental health perspectives PMID: 27548254