Environmental and genetic interactions in autism spectrum disorder: a literature review with a focus on air pollution

Autism Spectrum Disorder (ASD) is a neurodevelopmental condition which is associated with complex interactions between genetic susceptibility and environmental exposures. More recently, air pollution has been investigated as a modifiable risk factor and contributor to the neurodevelopmental outcomes of the disorder. This review focuses on the Middle East and North Africa (MENA) region and discusses genetic, immunologic, and epigenetic findings that help explain how pollutants, including particulate matter (PM₂.₅, PM₁₀), nitrogen oxides, ozone, and dioxins, contribute to the pathogenesis of ASD and its specific involvement in neuronal pathways. Many pollutants have been found to increase oxidative stress, neuroinflammation, and endocrine disruption which alters DNA methylation and histone modification patterns. The pathology of this involves activation of the aryl hydrocarbon receptor (AhR) and its downstream CYP1A1/CYP1B1 pathways which link environmental to altered gene expression and neural circuits. Current studies have shown that prenatal and early postnatal exposures are critical windows in which air pollutants can impair synaptogenesis, microglial regulation, and neurotransmitter balance. Significantly, sex-specific differences further modulate susceptibility, with males demonstrating heightened vulnerability due to hormonal and immune interactions. While progress has been made in uncovering these mechanisms, challenge in establishing causality and addressing diagnostic biases persists. Future directions should integrate longitudinal cohorts, omics-based biomarkers, and machine-learning models to clarify exposure-response relationships and guide personalized prevention strategies. Understanding how environmental and genetic factors converge to disrupt neurodevelopment is essential to mitigating ASD risk in increasingly polluted environments.