Environmental factors in the development of autism spectrum disorders: A reply to Sealey et al. (2016)

Sealey et al. have reviewed the available evidence on environmental factors that may predispose the development of autism spectrum disorders (ASD) in vulnerable populations. The authors identify exposure to vaccines, pesticides, and air pollutants as potential contributors. The author of this correspondence has previously proposed elsewhere that exposure to increasing levels of the agricultural and environmental pollutant, nitrous oxide (N2O), may be the dominant etiology of ASD and other neurodevelopmental disorders. N2O is thought to target the opioidergic system, including the Ƙ-opioid receptor (KOR). Exposure to thimerosal-containing vaccines may disrupt the activity of several endogenous targets as has been shown, principally including μ-opioid receptor (MOR). Given the antagonistic actions of the MOR and KOR, dysregulation of MOR may leave the heightened dynorphin/KOR system unchecked, possibly inducing a negative emotional state that is characteristic of ASD. Future attention may need to be focused on understanding on how early-life mercury exposures, such as in vaccines, may or may not reveal a gestational opiate dependence induced from other ASD-implicated environmental factors.