Environmental factors may contribute to up to a quarter of neurodevelopmental disorders, but more research into the role of specific substances is needed.
Genetic variables are thought to explain approximately 30% to 40% of autism cases, but more research is required to determine the role of environmental factors in causing the condition as well as other neurodevelopmental disorders (NDDs) such as ADHD, mental retardation, and dyslexia, according to an editorial published online on April 25, 2012, in Environmental Health Perspectives
. As the editorial notes, an expert committee assembled by the US National Academy of Sciences estimated that 3% of NDDs are directly caused by exposure to toxic substances and another 25% are caused by interactions between environmental factors and inherited susceptibilities.
Exploration of environmental causes of NDDs has been boosted by a growing awareness of the sensitivity of the developing human brain to toxic chemicals, especially during certain periods of embryonic and fetal development. For example, studies have linked the development of autism to rubella infection or taking medications such as thalidomide, misoprostol, and valproic acid during the first trimester of pregnancy. Epidemiological studies have also linked the development of autism with prenatal exposure to the organophosphate pesticide chlorpyrifos and to phthalates. Other studies have have linked lower IQ, dyslexia, and ADHD to exposure to lead, methylmercury, organophosphate pesticides, organochlorine pesticides, polychlorinated biphenyls, arsenic, manganese, polycyclic aromatic hydrocarbons, bisphenol A, brominated flame retardants, and perfluorinated compounds.
To help chart a strategy for discovering potentially preventable causes of autism and other NDDs, the authors note that the Mount Sinai Children’s Environmental Health Center convened a workshop that produced a list of 10 chemicals that are widespread in the environment and suspected of causing developmental neurotoxicity: lead, methylmercury, polychlorinated biphenyls, organophosphate pesticides, organochlorine pesticides, endocrine disruptors, automobile exhaust, polycyclic aromatic hydrocarbons, brominated flame retardants, and perfluorinated compounds.
To read the editorial, click here