Few rigorous epidemiologic studies have addressed the environmental causes and biologic underpinnings of autism spectrum disorder (ASD). The CHARGE (Childhood Autism Risks from Genetics and Environment) Study is a large, population-based case-control investigation of environmental risk factors, broadly defined, in relation to ASD and developmental delay without ASD symptoms, with referents from the general population. Fieldwork began in 2003, and by now CHARGE has published widely on exposures such as air pollution, mercury, flame retardants, maternal nutritional status in the peri-conception, untreated fever during pregnancy, mitochondrial dysfunction, candidate genes, a wide array of functional immune markers in both the child and the mother, and maternal metabolic conditions including obesity and diabetes. This last finding is notable, given the epidemic of obesity and type 2 diabetes that has occurred in parallel with the steady rise in ASD over the last few decades. Moreover, an emerging literature implicates several endocrine disrupting chemicals as contributing to obesity and metabolic dysregulation, including hyperinsulinemia, and to neurodevelopmental disorders as well. This project therefore builds upon these observations in several ways. First, obesity and type 2 or gestational diabetes will be examined in a larger sample, and glucose challenge test (GCT) results for the first time, to determine associations not only with development of ASD and intellectual impairment in the children, but also with specific speech and language delays, behavioral phenotypes such as attention deficits or hyperactivity, and gene expression. Second, these maternal metabolic conditions will be evaluated for associations with markers of both metabolic and immune dysregulation to be measured in neonatal bloodspots. Third, the predictive value of neonatal bloodspot markers for a later diagnosis of ASD or other child developmental and behavioral outcomes will be assessed. Fourth, the maternal metabolic conditions will be analyzed for potential links with upstream exposures to phthalates and anti- bacterial compounds, ubiquitous chemicals in common household products. Finally, this project will examine how gene variants that play a role in biochemical pathways relevant to the processes under study may influence susceptibility of the mother, the neonate or the child. To ensure adequate power for this analysis of gene-environment interaction, the sample size will be increased to 2400 children. This project addresses several goals set by the NIH Interagency Autism Coordinating Committee: 1) to discover environmental factors contributing to ASD, particularly in the prenatal period, 2) to understand biological mechanisms for ASD risk, including gene-by-environment interactions, and 3) to identify children at risk for ASD at earlier time points. Results of this detailed inquir into early exposures, maternal pathophysiology and prognostic markers in the newborn will set the stage for developing prevention strategies.
This project addresses several issues of direct public health relevance, and the science to be produced will lead to benefits in a wide cross-section of the U.S. population. Because obesity is reaching epidemic proportions and other metabolic conditions such as Type 2 diabetes, gestational diabetes, and dyslipidemia are rising steeply, understanding environmental causes has tremendous public health potential for moving us closer to effective prevention strategies. If environmental chemicals used in common household products do prove to adversely affect body weight, measures can be taken to either reformulate those products, removing them from the market, or to educate consumers on how to avoid them. Similarly, steady increases in ASD might be curbed if the postulated causal pathway is supported by the evidence.
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