What Causes Autism? Exploring the Genetic and Environmental Factors

Autism spectrum disorder is a complex condition with varying symptoms and severity, and there is no single known cause. Research suggests that autism develops from a combination of genetic and environmental influences. We cannot change genetics, but there are ways to limit exposure to certain environmental factors that have been linked to the development of autism. Studies have found a couple of environmental exposures that may contribute to autism spectrum disorder, such as lead, polychlorinated biphenyls (PCBs), automotive exhaust gases, and flame retardants.

However, no specific environmental factors have been identified that cause ASD. Maternal obesity, diabetes, and immune system disorders are some of the risk factors associated with autism. The Centers for Disease Control and Prevention (CDC) is currently conducting one of the largest studies in the US, called the Study to Explore Early Development (SEED), to analyze risk factors and behaviors related to ASD. CDC is also conducting a follow-up study of older children who enrolled in SEED to determine the health, functioning, and needs of people with ASD and other developmental disabilities as they mature.

Birth complications associated with trauma or ischemia and hypoxia have been strongly associated with ASD, while other pregnancy-related factors such as maternal obesity, diabetes, and caesarean section have shown a less strong (but significant) association with ASD risk. Animal studies provide evidence on the mechanisms by which particular factors increase or decrease the risk of autism. In addition to having a family member who has also been diagnosed with the condition, environmental factors such as severe pollution and being born prematurely are also risk factors for autism. Current evidence suggests that several environmental factors such as vaccination, maternal smoking, exposure to thimerosal, and assisted reproductive technologies are not related to the risk of ASD.

Autism Speaks remains firmly committed to advancing the understanding of genetic and environmental risk factors for autism. Future studies of ASD risk factors would benefit from a developmental psychopathology approach, prospective design, accurate measurement of exposure, reliable timing of exposure in relation to critical periods of development, and should take into account the dynamic interaction between gene and environment environment through the use of genetically informed designs.

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