Environmental influence on neurodevelopmental disorders: Potential association of heavy metal exposure and autism

Abstract

Environmental factors have been severally established to play major roles in the pathogenesis of neurodevelopmental disorders including autism spectrum disorder (ASD). ASD is a neurodevelopmental disorder that is associated with symptoms that reduce the quality of life of affected individuals such as social interaction deficit, cognitive impairment, intellectual disabilities, restricted and repetitive behavioural patterns. ASD pathogenesis has been associated with environmental and genetic factors that alter physiologic processes during development. Here, we review literatures highlighting the environmental impact on neurodevelopmental disorders, and mechanisms by which environmental toxins may influence neurodevelopment. Furthermore, this review discusses reports highlighting neurotoxic metals (specifically, lead, mercury, cadmium, nickel and manganese) as environmental risk factors in the aetiology of ASD. This work, thus suggests that improving the environment could be vital in the management of ASD.

Keywords: Autism; Environment; Metals; Neurodevelopmental disorders; Neurotoxicity.

Figure 1:. Potential mechanism of metal involvement in ASD pathogenesis.

A Schematic representation of mechanisms by which toxic environmental agents such as metals could be involved in ASD pathogenesis. These mechanisms have been implicated in the onset of ASD. Oxidative stress which is an imbalance between free radicals and antioxidants is one common mechanism by which metals exert their harmful effect in the brain. It results in a disproportionate energy production in neural cells. An interplay between these environmental agents and genes can also lead to alteration in the neurodevelopmental process. Aside the genes involved in neurodevelopment, certain hormones also have a role to play and an imbalance in the concentration of these have is implicated in the pathogenesis of ASD