Enter then the paper by Amy Kalkbrenner and colleagues [1] to proceedings, and their conclusion: "Our study adds to previous work in California showing a relation between traffic-related air pollution and autism, and adds similar findings in an eastern US state, with results consistent with increased susceptibility in the third-trimester". I might add that Dr Kalkbrenner has some research form when it comes to looking at environment and autism and has appeared on this blog before (see here).
Based on two datasets covering the east and west coasts of the United States (North Carolina and "the San Francisco Bay Area in California") including nearly 1000 children diagnosed with an autism spectrum disorder (ASD) and some 14,000 asymptomatic controls, researchers compared estimated exposure patterns based on birth addresses. Specifically, they looked at exposure to particulates "less than 10 μm (PM10)" within a period starting from preconception through to the child's first birthday. They also took into account a whole slew of geographic and demographic variables which potentially may have influenced results. They reported odds ratios (ORs) - adjusted ORs - which seemed to indicate that exposure, "a 10 μg/m increase in PM10", particularly during the third trimester of pregnancy was associated with increased susceptibility to autism. Ergo, more evidence for a potential link between prenatal air pollution exposure and offspring autism risk.
If I'm reading the Kalkbrenner paper correctly however, PM10 exposure during the first and second trimesters of pregnancy was not associated with autism. Indeed for the first trimester at least (bearing in mind the confidence intervals) the adjusted OR was "0.86 (95% CI = 0.74-0.99)" which I'll leave to readers to decide whether it was important or not.
There's little more for me to say about this area of autism research aside from the usual caveats applying regarding the use of estimated exposure patterns over and above actual individual exposure levels and the further requirement to elaborate on any mechanism potentially pertinent aside from any general description such as a role for oxidative stress or inflammatory markers [2]. I say this acknowledging the preliminary observations made about genotype, air pollution and autism risk [3] which still require independent follow-up.
In light of the my recent discussions on asthma being a potential risk factor for autism (see here) and further research on atopy and autism [4] which I'll be blogging about soon, one wonders whether other manifestations of air pollution exposure might also play some role in such findings. That combined with the more general developmental effects thought to be had as a result of air pollution exposure [5], and the whole thing starts to get rather complicated and in need of much greater scrutiny...
Music then and at the risk of [musically] repeating myself: Alice Cooper and No More Mr Nice Guy...
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[1] Kalkbrenner AE. et al. Particulate Matter Exposure, Prenatal and Postnatal Windows of Susceptibility, and Autism Spectrum Disorders. Epidemiology. 2014 Oct 3.
[2] Volk HE. et al. Residential proximity to freeways and autism in the CHARGE study. Environ Health Perspect. 2011 Jun;119(6):873-7.
[3] Volk HE. et al. Autism spectrum disorder: interaction of air pollution with the MET receptor tyrosine kinase gene. Epidemiology. 2014 Jan;25(1):44-7.
[4] Chen MH. et al. Is atopy in early childhood a risk factor for ADHD and ASD? A longitudinal study. J Psychosom Res. 2014 Oct;77(4):316-21.
[5] Calderón-Garcidueñas L. et al. Air pollution and detrimental effects on children's brain. The need for a multidisciplinary approach to the issue complexity and challenges. Front Hum Neurosci. 2014 Aug 12;8:613.
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Kalkbrenner AE, Windham GC, Serre ML, Akita Y, Wang X, Hoffman K, Thayer BP, & Daniels JL (2014). Particulate Matter Exposure, Prenatal and Postnatal Windows of Susceptibility, and Autism Spectrum Disorders. Epidemiology (Cambridge, Mass.) PMID: 25286049
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