The mediating role of the gut microbiome in the association between ambient air pollution and autistic traits.

Air pollution has been reported to be an environmental risk factor for autism spectrum disorder. However, the gut microbiome's role as a potential mediator has not been investigated. We aimed to clarify whether particulate matter with an aerodynamic diameter ≤10 µm (PM10) and nitrogen dioxide (NO2) exposure impact autistic traits through the gut microbiome. Using 170 mother-child pairs, PM10 and NO2 exposure levels during pregnancy (1st, 2nd, and 3rd trimesters) and annual residential PM10 levels at age 2, 4, and 6 years were estimated. Autistic traits and gut microbiome were assessed at age 6 years. The associations of PM10 or NO2 exposure, gut microbiome composition, and autistic traits were explored, and mediation analyses of statistically significant findings were also conducted. Exposure to PM10 during the 1st trimester of pregnancy was associated with increased autistic traits (10.6% change per interquartile range (IQR) increase, 95% confidence interval [CI]: 1.1, 21.0) and with Proteobacteria relative abundance at age 6 years (66.9% change per IQR increase, 95% CI: 21.3, 129.8). First trimester NO2 exposure was associated with autistic traits (12.1% change, 95% CI: 0.1, 25.5) and Proteobacteria relative abundance at age 6 years (48.1% change, 95% CI: -0.1, 119.6). Proteobacteria relative abundance was related to autistic traits (4.4% change per 2-fold increase, 95% CI: 1.3, 7.5). Relations between PM10 or NO2 exposure during the 1st trimester and autistic traits at age 6 years were partially mediated by Proteobacteria (proportion mediated 23.2%, p = 0.01 and 16.7%, p = 0.06; respectively). PM10 and possibly NO2 exposure during early pregnancy may affect autistic traits at age 6 years through the alteration of Proteobacteria abundance.