The Effect of Prenatal Air Pollution Exposure on Function and Severity in Children with Autism Spectrum Disorder

Background:   Autism spectrum disorder (ASD) often has a heterogeneous presentation and broad range of impairment. Environmental factors, specifically prenatal air pollution, have been associated with ASD as well as poorer neurodevelopmental outcomes and increased cognitive deficits in separate studies.

Objectives:  We examined the relationship between prenatal air pollution exposure and ASD severity, cognitive ability, and adaptive functioning among children with ASD. 

Methods:  Autism and ASD cases (N=331) from the Childhood Autism Risks from Genetics and the Environment (CHARGE) study were used for this analysis.  CHARGE is a population based case-control study of California born children with autism, developmental delay or typical development who were between 24 and 60 months old at the time of assessment. Residential histories were geo-coded and used to develop estimates of average air pollution exposures during pregnancy.  Regional air quality measures (NO₂, PM_2.5, PM₁₀, O₃) were assigned based on the EPA’s Air Quality Monitoring Network and near roadway air pollution estimates developed using the CALINE4 line-source air-quality dispersion model. We examined Mullen Scales of Early Learning (MSEL) composite and subscale scores, Vineland Adaptive Behavior Scales (VABS) composite and subscale scores, and the Autism Diagnostic Observation Schedule (ADOS)–derived Autism Severity Score as continuous phenotypes. 

Results:  Higher regional NO₂ (and, to a lesser extent, PM_2.5) exposures during pregnancy were associated with lower values of many of the phenotypes considered. A 2 standard deviation (SD) increase in NO₂ (6.5 ppb) was associated with decreases of 11% (95% CI: -20%, -2%) on the VABS composite score, 26% (95% CI: -34%, -8%) on the composite MSEL score, 14% (95% CI: -24%, -4%) on the VABS communication subscale, 40% (95% CI: -49%, -16%) on the MSEL expressive language subscale, and 31% (95% CI:-45%, -8%) on the  MSEL receptive language subscale. A 2 SD increase in PM_2.5 (6.7 µg/m³) was associated with decreases in the MSEL expressive and receptive language of 27% (95%CI: -52%, 1.6%) and 29% (95%CI: -59%, 1.6%), respectively.  Ozone, PM₁₀, and near roadway air pollution exposure were not associated with VABS or MSEL scores.  We did not find an association between air pollution exposure during pregnancy and the Autism Severity Score.

Conclusions:  These results suggest that NO₂ exposure during pregnancy may result in increased impairment, and specifically in more severe language and communication deficits, among children with ASD.