Research

There is still a lot to learn about ASD. Research on ASD 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 ASD through research. Like the many families living with ASD, CDC considers ASD an important public health concern. CDC is committed to continuing to provide essential data on ASD, search for risk factors and causes, and develop resources that help identify children with ASD 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).

Determining How Many People Have ASD

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

By studying the number of children with ASD at different points in time, CDC can find out if the number is rising, dropping, or staying the same. We also can compare the number of children with ASD in different areas of the country and among different groups of people. This information can help direct our research into potential factors that might put children at risk for ASD, 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 ASD:

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 ASD 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).

Learn more about ADDM »

Article: Prevalence of Autism Spectrum Disorder Among Children Aged 8 Years — Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2014

Community Report: 2018 Community Report from the Autism and Developmental Disabilities Monitoring Network

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.

Learn more about MADDSP »

Evaluating CDC’s Tracking System

CDC evaluated the tracking system that is used to estimate the prevalence of ASD. 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 ASD.
• 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 Disorder

National Surveys

CDC conducts the National Health Interview Survey (NHIS), a nationally representative survey that provides data on the health of children in the United States (including information on developmental disabilities and delays).

Learn more about NHIS »

CDC also collaborates on the development and management of other nationally representative surveys sponsored by the Maternal and Child Bureau of the U.S. Health Resources and Services Administration: the National Survey of Children’s Health (NSCH) and the National Survey of Children with Special Health Care Needs (NSSHCN). These surveys also provide data on children’s health and development.

Learn more about NSCH »
Learn more about NSCSHCN »

CDC has used data from these national surveys to conduct a range of studies on the prevalence of developmental disabilities, demographic characteristics of children with developmental disabilities, health and health care needs of children with developmental disabilities, and family impacts of parenting a child with special needs.

Read publications that used national surveys »

Evaluating Changes in the Prevalence of Autism Spectrum Disorder (ASD)

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 about what seemed to be a larger than expected number of children with autism spectrum disorder (ASD) in Brick Township. CDC and the Agency for Toxic Substances and Disease Registry (ATSDR) worked together to find out how common ASD were in Brick Township and to study the possible relationship of environmental factors to ASD in the community.

The prevalence of ASD in Brick Township was 6.7 per 1,000 children. This was higher than prevalence estimates from other studies conducted at that time, particularly studies conducted in the United States. However, the prevalence of ASD in Brick Township was within the range of studies that used more thorough case-finding methods among smaller populations.

Read publications and reports from the Brick Autism Project [PDF – 96KB]

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Understanding Risk Factors and Causes

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

• Most scientists agree that genes are one of the risk factors that can make a person more likely to develop ASD.¹
• Children who have a sibling with ASD are at a higher risk of also having ASD. ^2-7
• ASD tends to occur more often in people who have certain genetic or chromosomal conditions, such as fragile X syndrome  or tuberous sclerosis.^8-15
• When taken during pregnancy, the prescription drugs valproic acid and thalidomide have been linked with a higher risk of ASD.^12-13
• There is some evidence that the critical period for developing ASD occurs before, during, and immediately after birth. ¹⁴
• Children born to older parents are at greater risk for having ASD.¹⁵

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 ASD 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 »

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Vaccine Safety

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

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 ASD, see:

• CDC Studies on Thimerosal in Vaccines
• Immunization Safety Office
  • Vaccine Safety: Concerns About Autism
  • Mercury and Vaccines (Thimerosal)
  • Measles, Mumps, and Rubella (MMR) Vaccines Safety
  • Thimerosal in Seasonal Influenza Vaccine
  • Timeline: Thimerosal in Vaccines (1999–2010)

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International Research

The CDC-Denmark Program (Project Completed)

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]

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References

1. Huquet G, Ey E, Bourgeron T. The genetic landscapes of autism spectrum disorders. Annu Re Genomics Hum Genet. 2013; 14: 191-213.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. DiGuiseppi C, Hepburn S, Davis JM, Fidler DJ, Hartway S, Lee NR, Miller L, Ruttenber M, Robinson C. Screening for autism spectrum disorders in children with Down syndrome. J Dev Behav Pediatr. 2010; 31: 181-191.
9. Cohen D, Pichard N, Tordjman S, Baumann C, Burglen L, Excoffier E, Lazar G, Mazet P, Pinquier C, Verloes A, Heron D. Specific genetic disorders and autism: Clinical contribution towards their identification. J Autism Dev Disord. 2005; 35(1): 103-116.
10. Hall SS, Lightbody AA, Reiss AL. Compulsive, self-injurious, and autistic behavior in children and adolescents with fragile X syndrome. Am J Ment Retard. 2008; 113(1): 44-53.
11. Zecavati N, Spence SJ. Neurometabolic disorders and dysfunction in autism spectrum disorders. Curr Neurol Neurosci Rep. 2009; 9(2): 129-136.
12. Christensen J, Grønborg TK, Sørensen MJ, Schendel D, Parner ET, Pedersen LH, Vestergaard M. Prenatal valproate exposure and risk of autism spectrum disorders and childhood autism. JAMA. 2013; 309(16): 1696-1703.
13. Strömland K, Nordin V, Miller M,  Akerström B, Gillberg C. Autism in thalidomide embryopathy: a population study. Dev Med Child Neurol. 1994; 36(4): 351-356.
14. Gardener H, Spiegelman D, Buka SL. Perinatal and neonatal risk factors for autism: a comprehensive meta-analysis. Pediatrics. 2011; 128(2): 344-355.
15. Durkin MS, Maenner MJ, Newschaffer CJ, Lee LC, Cunniff CM, Daniels JL, Kirby RS, Leavitt L, Miller L, Zahorodny W, Schieve LA. Advanced parental age and the risk of autism spectrum disorder. Am J Epidemiol. 2008; 168(11): 1268-1276.

Glossary

Genes:Each cell in the human body contains thousands of genes. Genes have a special code called DNA that determines many things about the person. For example, whate people will look like and whether they are likely to have certain illnesses.

Thalidomide: According to the U.S. Food and Drug Administration (FDA), thalidomide is a drug that was marketed outside of the United States in the late 1950’s and early 1960’s. It was used as a sleeping pill, and to treat morning sickness during pregnancy. However, its use by pregnant women resulted in the birth of thousands of babies with severe malformations. Thalomid (thalidomide) is approved in the U.S. to treat the painful, disfiguring skin sores associated with leprosy, and to prevent and control the return of these skin sores. Distribution of and access to thalidomide is strictly controlled to prevent its use during pregnancy. A pregnant woman or any woman thinking about becoming pregnant must not take Thalomid (thalidomide), because it is known to cause severe birth defects or death to an unborn baby, even after taking just one dose. When a woman of child-bearing age has no other appropriate treatment choice and must take Thalomid (thalidomide), there are many precautions that must be taken to avoid pregnancy. To view these steps and to find out additional information, go to http://www.fda.gov/cder/news/thalinfo/thalfaq.htm.