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Your Environment. Your Health.

Autism

Autism

Introduction

Photo of a child with autism

Autism,1 also known as autism spectrum disorder (ASD), is a disorder2 that causes impairment in social interaction, as well as the presence of repetitive, restricted behaviors and interests. It is usually first diagnosed in early childhood.

The term spectrum refers to the wide range of symptoms, skills, and levels of impairment that those with ASD can have. Some are mildly impaired by their symptoms, while others are severely disabled. According to the Centers for Disease Control and Prevention, ASD affects roughly 1 in 68 children.3

The Autism and the Environment(525KB) fact sheet provides a summary of NIEHS-supported research on autism.

What are some of the symptoms of autism?

Although people with autism have a range of symptoms that vary in severity, they all have difficulties communicating and interacting with others, and show restricted and repetitive patterns of behavior and interests. Most symptoms are noticeable by the time a child is 2-3 years old, but many children are not diagnosed until later. Early intensive behavioral intervention can improve communication, learning, and social skills in children with autism.

Autism affects people for their entire lives, and often comes with other conditions, such as epilepsy, sleep disturbances, and gastrointestinal problems. Currently, no drugs have proven effective for treating core autism symptoms.

How is autism diagnosed?

In 2013 the American Psychiatric Association updated the criteria for diagnosing ASD in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).

The new DSM-5 criteria encourage diagnosis prior to school age. Children with ASD must show symptoms from early childhood, although the symptoms may not be recognized until later. Sometimes symptoms are not evident until children are old enough to be in social situations that challenge their capacity to respond.

What causes autism?

Although recent studies indicate that the rate of ASD is rising, the causes of these disorders are not well-understood. Over time, scientists have found that rare gene changes, or mutations, as well as small common genetic variations, are associated with ASD, thus implying a genetic component. However, a growing area of research indicates that ASD may be caused by an interaction of genetic and environmental factors.

For example, one hypothesis states that ASD may be triggered by a mother’s exposure to environmental agents while pregnant. These exposures, in turn, could cause or contribute to the child’s development of ASD.

Related studies on ASD, genes, and the environment

What are some of the environmental factors researchers believe may be associated with autism?

The clearest evidence for environmental risk factors in ASD involves events before and during birth. They may include:

  • Advanced parental age at time of conception
  • Prenatal exposure to air pollution
  • Maternal obesity or diabetes
  • Extreme prematurity and very low birth weight
  • Any birth difficulty leading to periods of prenatal oxygen deprivation to the baby’s brain
  • Prenatal exposure to certain pesticides

Again, however, these factors alone are unlikely to cause ASD. Rather, they appear to increase a child’s chances for developing ASD, when combined with the aforementioned genetic factors.

Environmental factors play a role in autism

Air pollution

Work supported by NIEHS indicates that early-life exposure to air pollution is a risk factor for autism.

Prenatal conditions

Researchers funded by NIEHS discovered that problems with the immune system, as well as maternal conditions during pregnancy, are linked with higher autism risk.

Nutrition

According to NIEHS-funded research, prenatal vitamins may help lower autism risk.

Mercury and other contaminants

There continues to be concern about autism and mercury exposure. NIEHS funds research examining exposure to mercury and other contaminants.

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What is NIEHS Doing?

NIEHS has steadily increased funding of autism research over the last decade, and this investment is producing important new discoveries that may help prevent autism. For example, NIEHS-funded researchers have shown that taking folic acid and avoiding infections during pregnancy can help lower autism risk. Researchers have also shown that problems with the immune system are involved in autism, and that early-life exposure to high levels of air pollution may increase risk, especially for children whose genetic makeup causes them to be more susceptible.

The NIEHS Autism Research Program has attracted talented scientists from toxicology, epidemiology, and other areas. These researchers are using new ways to measure prenatal exposures, screen for contaminants that affect brain development, and understand how environmental factors interact with genes to lead to autism.

Notable NIEHS studies on ASD

A team of NIEHS-funded scientists at the University of California (UC), Davis are searching to address the environmental contributors to ASD through their continued work on the Childhood Autism Risk from Genetics and the Environment (CHARGE) Study.

CHARGE is an ongoing exploration of more than 1,800 children, to clarify the roles of genetics and environmental exposures in ASD development. Recently published findings from CHARGE showed that pregnant women who lived near farms using certain pesticides were more likely to have children with ASD or developmental delay than pregnant women who lived more than 1.5 kilometers from farms using these pesticides.

In a separate study led by NIEHS-funded scientists from the University of Southern California, researchers found that children possessing a specific genetic risk factor appear more likely to develop ASD when exposed to high levels of air pollution while in the womb. This finding helps explain why some previous studies that focused exclusively on genetic variation and ASD development have proven inconclusive.

NIEHS involvement with the IACC

NIEHS is one of the federal members of the Interagency Autism Coordinating Committee (IACC). Dr. Linda Birnbaum, NIEHS director, is the primary NIEHS representative to the IACC and Dr. Cindy Lawler, chief of the NIEHS Genes, Environment, and Health branch, is the alternate.

NIEHS works in partnership with other members of the IACC to summarize advances in autism research and participate in strategic planning for research needs. The IACC hears directly from members of the public regarding their concerns about autism and recommendations for research needs.

Further Reading

Stories from the Environmental Factor (NIEHS Newsletter)

Printable Fact Sheets

Press Releases

Additional Resources

  • Autism and The Environment Meeting Report(205KB) (September 2010)
    To identify novel opportunities and mechanisms to accelerate research on environmental factors and autism, a diverse group of scientists came together on September 8, 2010 at the National Institute of Environmental Health Sciences (NIEHS) Keystone Campus in Durham, NC to share ideas and expertise.
  • NIEHS Virtual Forum: Autism and the Environment (April 2014)
    NIEHS hosted a virtual forum on autism spectrum disorders and the environment on April 22, 2014.

Related Health Topics

  1. Lyall K, Schmidt RJ, Hertz-Picciotto I. 2014. Maternal lifestyle and environmental risk factors for autism spectrum disorders. Int J Epidemiol43(2):443-464. [Abstract]
  2. Jeste SS, Geschwind DH. 2014. Disentangling the heterogeneity of autism spectrum disorder through genetic findings. Nat Rev Neurol 10(2):74-81. [Abstract]
  3. Developmental Disabilities Monitoring Network Surveillance Year 2010 Principal Investigators; Centers for Disease Control and Prevention (CDC). 2014. Prevalence of autism spectrum disorder among children aged 8 years - autism and developmental disabilities monitoring network, 11 sites, United States, 2010. MMWR Surveill Summ 63(2):1-21. [Abstract]
  4. Volk HE, Hertz-Picciotto I, Delwiche L, Lurmann F, McConnell R. 2011. Residential proximity to freeways and autism in the CHARGE study. Environ Health Perspect 119(6):873-877. [Abstract]
  5. Volk HE, Lurmann F, Penfold B, Hertz-Picciotto I, McConnell R. 2013. Traffic-related air pollution, particulate matter, and autism. JAMA Psychiatry 70(1):71-77. [Abstract]
  6. Volk HE, Kerin T, Lurmann F, Hertz-Picciotto I, McConnell R, Campbell DB. 2014. Autism spectrum disorder: interaction of air pollution with the MET receptor tyrosine kinase gene. Epidemiology 25(1):44-47. [Abstract]
  7. Nordahl CW, Braunschweig D, Iosif AM, Lee A, Rogers S, Ashwood P, Amaral DG, Van de Water J. 2013. Maternal autoantibodies are associated withabnormal brain enlargement in a subgroup of children with autism spectrum disorder. Brain Behav Immun 30:61-65. [Abstract]
  8. Krakowiak P, Walker CK, Bremer AA, Baker AS, Ozonoff S, Hansen RL, Hertz-Picciotto I. 2012. Maternal metabolic conditions and risk for autism and other neurodevelopmental disorders. Pediatrics 129(5):e1121-e1128. [Abstract]
  9. Brown AS, Sourander A, Hinkka-Yli-Salomaki S, McKeague IW, Sundvall J, Surcel HM. 2014. Elevated maternal C-reactive protein and autism in anational birth cohort. Mol Psychiatry 19(2):259-264. [Abstract]
  10. Schmidt RJ, Hansen RL, Hartiala J, Allayee H, Schmidt LC, Tancredi DJ, Tassone F, Hertz-Picciotto I. 2011. Prenatal vitamins, one-carbon metabolismgene variants, and risk for autism. Epidemiology 22(4):476-485. [Abstract]
  11. Schmidt RJ, Tancredi DJ, Ozonoff S, Hansen RL, Hartiala J, Allayee H, Schmidt LC, Tassone F, Hertz-Picciotto I. 2012. Maternal periconceptionalfolic acid intake and risk of autism spectrum disorders and developmental delay in the CHARGE (CHildhood Autism Risks from Genetics and Environment) case-control study. Am J Clin Nutr 96(1):80-89. [Abstract]
  12. Van Wijngaarden E, Davidson PW, Smith TH, Evans K, Yost K, Love T, Thurston SW, Watson GE, Zareba G, Burns CM, Shamlaye CF, Myers GJ. 2013. Autism spectrum disorder phenotypes and prenatal exposure to methylmercury. Epidemiology 24(5):651-659. [Abstract]
  13. Hertz-Picciotto I, Green PG, Delwiche L, Hansen R, Walker C, Pessah IN. 2010. Blood mercury concentrations in CHARGE Study children with andwithout autism. Environ Health Perspect 118(1):161-166. [Abstract]

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