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Photo of a child with autism


Autism, also known as ASD, is a spectrum of disorders 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.

What are some of the symptoms of ASD?

People with ASD may show deficits in a wide range of areas including:

  • Social interaction
  • Verbal and nonverbal communication

How is ASD diagnosed?

Historically, those with ASD were placed into one of four related, yet distinctly separate, diagnostic subtypes:

  • Autistic disorder
  • Childhood disintegrative disorder
  • Pervasive developmental disorder – not otherwise specified (PDD-NOS)
  • Asperger syndrome

In 2013, however, the American Psychiatric Association released the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), which replaced these subtypes with the current spectrum system.

What causes ASD?

Although recent studies indicate that the rate of ASD appears on the rise, 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 ASD?

The clearest evidence for environmental risk factors in autism 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.

What NIEHS is Doing on Autism 

NIEHS is dedicated to identifying the environmental factors that increase ASD risk, while also understanding when they have the most influence and who is the most susceptible to their effects.

To that end, NIEHS currently invests more than $7.5 million, annually, in ASD research.

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.

Through an array of interdisciplinary approaches, UC Davis researchers hope to:

  • Identify specific environmental agents that affect risk of ASD
  • Learn how those exposures affect basic mechanisms of brain development
  • Examine the role of immune system dysfunction in ASD

To learn more about the CHARGE Study, please visit the following resources:

In a second 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 during gestation. This finding helps explain why some previous studies that focused exclusively on genetic variation and ASD development have proven inconclusive.

The study was published in the January 2014 issue of the journal Epidemiology, and is available online, along with a companion article in the NIEHS newsletter, the Environmental Factor.

Other ASD stories from the Environmental Factor:

NIEHS press releases on ASD

General Information 

Related Topics 

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