Assessing the Relation between Plasma PCB Concentrations and Elevated Autistic Behaviour Using Bayesian Predictive Odds Ratios

Abstract

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by impaired social communication and repetitive or stereotypic behaviours. In utero exposure to environmental chemicals, such as polychlorinated biphenyls (PCBs), may play a role in the etiology of ASD. We examined the relation between plasma PCB concentrations measured during pregnancy and autistic behaviours in children aged 3-4 years old in the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a pregnancy and birth cohort of 538 mother-infant pairs from Canada (enrolled: 2008-2011). We quantified the concentrations of 6 PCB congeners in plasma samples collected during the 1st trimester. At age 3-4 years, caregivers completed the Social Responsiveness Scale-2 (SRS), a valid and reliable measure of children’s reciprocal social and repetitive behaviors and restricted interests. We examined SRS scores as both a continuous and binary outcome and calculated Bayesian predictive odds ratios for more autistic behaviour based on a latent variable model with a threshold SRS >60. We found very small and imprecise increases in the mean SRS score for the highest quartile of plasma PCB concentrations compared to the lowest quartile, but these were accompanied by larger increases in the odds of more autistic behaviour. For instance, an average increase of 0.7 [95%CI: -0.8, 2.3] in the mean SRS (Q4 versus Q1) for PCB138 translated to an odds ratio of 1.5 [95%CI: 0.9, 2.3]. In conclusion, we found some evidence that plasma PCB concentrations during pregnancy may be associated with small increases in autistic behaviours in this cohort. Our findings demonstrate the importance of measuring associations between PCBs and autistic behaviour on both continuous and binary scales.