Research

There is still a lot to learn about ASDs. Research on ASDs has increased a great deal in recent years and CDC is part of the larger group of public and private organizations working to better understand ASDs through research. Like the many families living with ASDs, CDC considers ASDs an important public health concern. CDC is committed to continuing to provide essential data on ASDs, search for risk factors and causes, and develop resources that help identify children with ASDS as early as possible.

Recent efforts to coordinate autism research are reflected in the "Strategic Plan for Autism Spectrum Disorder Research" by the Interagency Autism Coordinating Committee (IACC).

What is Surveillance?

Watch this video to learn more.

Determining How Many People Have ASDs

More people than ever before are being diagnosed with an ASD. It is unclear how much of this increase is due to a broader definition of ASDs and better efforts in diagnosis. However, a true increase in the number of people with an ASD cannot be ruled out. We believe the increase in ASD diagnosis is likely due to a combination of these factors.

By studying the number of children with ASDs at different points in time, we at CDC can find out if the number is rising, dropping, or staying the same. We also can compare the number of children with ASDs in different areas of the country and among different groups of people. This information can help direct our research into potential risk factors and can help communities direct their outreach efforts to those who need it most.

Following are activities that CDC conducts or funds in order to learn more about the number of people with ASDs:

Autism and Developmental Disabilities Monitoring (ADDM) Network

The ADDM Network is a group of programs funded by CDC to estimate the number of children with ASDs and other developmental disabilities living in different areas of the United States. The ADDM Network sites all collect data using the same surveillance methods, which are modeled after CDC’s Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP).

CDC estimates that 1 in 88 children has been identified with an ASD. This data comes from the ADDM Network, which estimated the number of 8-year-old children with ASDs living in 14 communities throughout the United States in 2008.

Read articles from the ADDM Network »

Learn more about ADDM »

Article: Prevalence of Autism Spectrum Disorders, 2008

ADDM Community Report [PDF - 4.42MB]

Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP)

MADDSP was established to determine all children who have one or more of four developmental disabilities -- intellectual disability, cerebral palsy, hearing loss, and vision impairment -- in the metropolitan Atlanta area.  Autism spectrum disorder was added as a fifth disability beginning in the 1996 study year. 

CDC estimates that about 1 in 84 children has been identified with an ASD in metropolitan Atlanta.

Learn more about MADDSP »

Evaluating CDC’s Tracking System

CDC evaluated the tracking system that is used to estimate the prevalence of ASDs. Validation studies that evaluate tracking systems, such as this one, allow CDC to make informed changes in order to provide the most complete prevalence estimates.

Important findings from the study include:

• The CDC tracking system is likely not over-estimating the prevalence of ASDs.
• Most children found to have an ASD by a clinical examination were also detected by the tracking system.
• The CDC tracking system missed 12 of 177 children who were examined and found to have an ASD. This result shows we are likely not counting some children with ASD.

Learn more about the evaluation study »

Article: Evaluation of a Records-Review Surveillance System Used to Determine the Prevalence of Autism Spectrum Disorders

National Surveys

CDC conducts two nationally representative surveys that provide data on health conditions in U.S. children: the National Survey of Children’s Health (NSCH) and the National Health Interview Survey (NHIS).

Estimates of diagnosed autism in 2003-2004 were 5.7 per 1,000 school-age children from the National Health Interview Survey and 5.5 per 1,000 school-age children from the National Survey of Children's Health. Both surveys showed that boys were nearly four times more likely than girls to have been diagnosed with autism.

• Mental Health in the United States: Parental Report of Diagnosed Autism in Children Aged 4-17 Years - United States, 2003—2004 [Read article]
• Fact sheet [PDF - 86.2KB]

In addition, the Health Resources and Services Administration (HRSA) released a paper in October 2009 on parent-reported diagnosis of ASDs using data from the National Survey of Children’s Health.  The report  indicated that approximately 1% of children are affected with an ASD. [Read summary]

Early ASD Surveillance Development Project

CDC is funding two sites—the California Department of Health Services and Florida State University—to develop and test projects to identify the number of children under 4 years of age with ASDs. These projects will help find ways to get a more accurate picture of the prevalence of ASDs at earlier ages.

Evaluating Changes in the Prevalence of Autism Spectrum Disorders (ASDs)

To provide a forum for sharing the latest information on ASD prevalence changes, CDC and Autism Speaks co-hosted the “Workshop on U.S. Data to Evaluate Changes in the Prevalence of Autism Spectrum Disorders (ASDs)” on February 1, 2011. The workshop brought together scientists and stakeholders from the autism community to increase knowledge about ASD prevalence, to learn from other conditions, and to share ideas on how to move forward to better understand ASD trends. An executive summary and the complete workshop summary are available for download here:

Executive Summary [PDF - 392KB]
Complete Workshop Summary [PDF - 1.12MB]

Brick Autism Project (Project Completed)

In late 1997, a citizen’s group in Brick Township, New Jersey, told the state Department of Health and Senior Services (DHSS) about what seemed to be a larger-than-expected number of children with autism in Brick Township.  CDC and the Agency for Toxic Substances and Disease Registry (ATSDR) worked together to find out how common ASDs were in Brick Township and to study the possible relationship of environmental factors to ASDs in the community.

The prevalence of ASDs was 6.7 per 1000 children. The prevalence of ASDs in Brick Township seems to be higher than that in other studies, particularly studies conducted in the United States, but within the range of a few recent studies in smaller populations that used more thorough case-finding methods.

• Prevalence of Autism in a United States Population: The Brick Township, New Jersey, investigation [Read article ]
• Public Health Assessment: Brick Township Investigation [Read report]
• Prevalence of Autism in Brick Township, New Jersey, 1998: Community Report [Read report] 
• Investigation of the Prevalence of Autism in Brick Township - A link to similar findings [Read article] 
• Results of Brick Township Investigation of Environmental Pathways - A Public Health Assessment - A link to similar findings [Read article]

Understanding Risk Factors and Causes

We do not know all of the causes of ASDs.  However, we have learned that there are likely many causes for multiple types of ASDs.  There may be many different factors that make a child more likely to have an ASD, including environmental, biologic and genetic factors.

What Research Tells Us

• Most scientists agree that genes are one of the risk factors that can make a person more likely to develop an ASD. Studies have shown that:  
  • Studies have shown that among identical twins, if one child has an ASD, then the other will be affected about 36-95% of the time. In non-identical twins, if one child has an ASD, then the other is affected about 0-31% of the time. ^[1-4]
  • Parents who have a child with an ASD have a 2%–18% chance of having a second child who is also affected.^[5,6]
• ASDs tend to occur more often in people who have certain other medical conditions.  About 10% of children with an ASD have an identifiable genetic, neurologic, or metabolic disorder, such as:
  • Fragile X syndrome
  • Tuberous sclerosis
  • Down syndrome
  • Other chromosomal disorders

• When taken during pregnancy, the prescription drugs valproic acid and thalidomide have been linked with a higher risk of ASDs.
• We know that the once common belief that poor parenting practices cause ASDs is not true.
• There is some evidence that the critical period for developing ASDs occurs before birth.  However, concerns about vaccines and infections have led researchers to consider risk factors before and after birth.
• A small percentage of children who are born prematurely or with low birthweight are at greater risk for having ASDs.

Study to Explore Early Development (SEED)

SEED is a multi-year study funded by CDC. It is currently the largest study in the United States to help identify factors that may put children at risk for ASDs and other developmental disabilities. Understanding the risk factors that make a person more likely to develop an ASD will help us learn more about the causes.

The six SEED study sites and a data coordinating center are part of the Centers for Autism and Developmental Disabilities Research and Epidemiology (CADDRE) network.

Learn more about SEED »

Learn more about CADDRE »

What is Epidemiology?

Watch this video to learn more.

Vaccines  

Many studies have looked at whether there is a relationship between vaccines and autism spectrum disorders (ASDs). To date, the studies continue to show that vaccines are not associated with ASDs.

However, CDC knows that some parents and others still have concerns. To address these concerns, CDC is part of the Inter-Agency Autism Coordinating Committee (IACC), which is working with the National Vaccine Advisory Committee (NVAC) on this issue. The job of the NVAC is to advise and make recommendations regarding the National Vaccine Program. Communication between the IACC and NVAC will allow each group to share skills and knowledge, improve coordination, and promote better use of research resources on vaccine topics.

For more information about vaccines and ASDs, see:

• Chart of CDC’s Vaccine and ASD Research [PDF - 46KB]
• Immunization Safety Office
  • CDC Statement on Autism and Thimerosal 
  • Measles, Mumps, and Rubella (MMR) Vaccine and Autism
  • Thimerosal in Seasonal Influenza Vaccine
  • Timeline: Thimerosal in Vaccines (1999–2008)
• National Network for Immunization Information
  • MMR Vaccine and Autism
  • Mercury and Vaccines

International Research

The CDC-Denmark Program

The CDC–Denmark Program was set up to look at many public health issues. The program highlights the work done using Danish national public health data systems. These systems are not found anywhere else. They include more than 200 long-term disease and administrative registries. They also include the stored newborn blood samples of all children born in Denmark from 1982 onward. These systems are linked with one another. Thus, they can be used to make data sets with information on very large numbers of people. These data sets cover long periods of time. Therefore, they can be used to look at health trends and disease traits. They can also be used to study less common risk factors or diseases in more detail and with more accuracy than can be done anywhere else.

Learn more about this program » [PDF - 75KB]

References

1. Rosenberg RE, Law JK, Yenokyan G, McGready J, Kaufmann WE, Law PA. Characterisitics and concordance of autism spectrum disorders among 277 twin pairs. Arch Pediatr Adolesc Med. 2009; 163(10): 907-914.
2. Hallmayer J, Cleveland S, Torres A, Phillips J, Cohen B, Torigoe T, Miller J, Fedele A, Collins J, Smith K, Lotspeich L, Croen LA, Ozonoff S, Lajonchere C, Grether JK, Risch N. Genetic heritability and shared environmental factors among twin pairs with autism. Arch Gen Psychiatry. 2011; 68(11): 1095-1102.
3. Ronald A, Happe F, Bolton P, Butcher LM, Price TS, Wheelwright S, Baron-Cohen S, Plomin R. Genetic heterogeneity between the three components of the autism spectrum: A twin study. J. Am. Acad. Child Adolesc. Psychiatry. 2006; 45(6): 691-699.
4. Taniai H, Nishiyama T, Miyahci T, Imaeda M, Sumi S. Genetic influences on the board spectrum of autism: Study of proband-ascertained twins. Am J Med Genet B Neuropsychiatr Genet. 2008; 147B(6): 844-849.
5. Ozonoff S, Young GS, Carter A, Messinger D, Yirmiya N, Zwaigenbaum L, Bryson S, Carver LJ, Constantino JN, Dobkins K, Hutman T, Iverson JM, Landa R, Rogers SJ, Sigman M, Stone WL. Recurrence risk for autism spectrum disorders: A Baby Siblings Research Consortium study. Pediatrics. 2011; 128: e488-e495.
6. Sumi S, Taniai H, Miyachi T, Tanemura M. Sibling risk of pervasive developmental disorder estimated by means of an epidemiologic survey in Nagoya, Japan. J Hum Genet. 2006; 51: 518-522.