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
- Maternal lifestyle and environmental risk factors for autism spectrum disorders (International Journal of Epidemiology)
- Disentangling the heterogeneity of autism spectrum disorder through genetic findings (Nature Reviews, Neurology)
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.
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:
- CHARGE: A Study to Understand the Causes of Autism and Other Developmental Disorders (English)(1MB)
- CHARGE: A Study to Understand the Causes of Autism and Other Developmental Disorders (Spanish)(614KB)
- Childhood Autism Risks from Genetics and the Environment: The CHARGE Study(4MB)
- Neurodevelopmental Disorders and Prenatal Residential Proximity to Agricultural Pesticides: The CHARGE Study (from the journal, Environmental Health Perspectives)
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.
Other ASD stories from the Environmental Factor:
- Autism studies build on past investments and guide future research(January 2014)
- New evidence of gene-environment interaction in autism (January 2014)
- Parents are right: children with autism experience more GI symptoms (January 2014)
- Autism in Minneapolis higher among Somalis and whites than other groups (January 2014)
- Webinar highlights advances in the study of autism (September 2013)
- Prenatal inflammation linked to autism risk (February 2013)
- A Conversation on the State of Autism Research (December 2011)
- A Genomics Approach Toward Understanding Autism (December 2011)
NIEHS press releases on ASD
- Prenatal Inflammation Linked to Autism Risk (Jan. 24, 2013)
- Autism and The Environment Meeting Report(189KB)(September 2010)
- Healthy People
- NIEHS Virtual Forum: Autism and the Environment(April 2014)
- Talking to Your Doctor - Resources from NIH