What is autism?

* Autism is a complex, life-long biological disorder of development that results in social interaction problems, communication difficulties, and restrictive or repetitive interests and behaviors. The prevalence of autism estimates run from approximately one-in-500 children, to one-in-1000 children, who might be affected by some form of the disorder.* (See the reference listed in the Autism and Vaccine Research fact sheet.)

* Autism can be reliably diagnosed by or before age three. Parents and expert clinicians can usually detect symptoms during infancy, although a formal diagnosis is generally not made until the child fails to develop functional language by age two. Approximately 20 percent of children with autism reportedly experience a "regression"; that is, they have apparently normal development followed by a loss of communication and social skills.

* Boys are three-to-four times more likely to be affected by autism than girls. Autism occurs in all racial, ethnic, and social groups.

* Although there is currently no known cure for autism, autism is treatable. Persons with autism can make progress if they receive appropriate, individual intervention. Pre-school children who receive intensive, individualized, behavioral interventions show remarkable progress. ** (See the reference listed in Autism and Vaccine Research fact sheet.) In addition, limited pharmacological interventions are available to treat specific symptoms of autism.

What causes autism?

* In the majority of cases, no specific underlying cause can be identified. However, a variety of factors are being investigated. These include infectious, metabolic, genetic, and environmental factors.

* A working group convened by the NIH in 1995 reached a consensus that autism probably results from a genetic susceptibility that involves multiple genes.

* To date, genetic causes for one disorder commonly accompanied by autism and one autism-spectrum disorder have been identifiedCFragile X and Rett syndrome, respectivelyCand genetic "hotspots" for more classic autism have been indicated. Fragile X is the most common, genetically inherited form of mental retardation currently known and produces many of the same behaviors and symptoms as autism. Rett syndrome, which affects only girls, is a progressive brain disease that produces a loss of language/social skills that is similar to autism and is classified as an autism spectrum disorder (ASD).*** (See the reference listed in the Autism and Vaccine Research fact sheet.)

* NIH research on possible genetic, infectious, immunological, and environmental causes and mechanisms of autism is underway.

Is there a relationship between autism and vaccines?

* To date there is no conclusive evidence that any vaccine increases the risk of developing autism or any other behavior disorder.

* Several epidemiological studies show no causal association between the measles/mumps/rubella (MMR) vaccine (or other measles-containing vaccines) and autism. In January 1990, the Institute of Medicine concluded that there was no evidence to indicate a causal relationship between autism and the diphtheria/tetanus/pertussis (DTP) vaccine or the pertussis component of the DTP vaccine. In 2001, the IOM concluded that there is no causal relationship, at a population level, between the MMR vaccine and ASDs.

* Currently, no study provides definitive evidence of an association between autism and vaccines. However, continued research is needed to examine the mechanisms of autism and any possible relationship to vaccines.

For more information on autism and autism research, contact the National Institute of Child Health and Human Development (NICHD) Clearinghouse, at 1-800-370-2943, or visit the NICHD web site at http://www.nichd.nih.gov/. You can also obtain autism information through the National Library of Medicine's MEDLINEPlus, at http://medlineplus.nlm.nih.gov/medlineplus/autism.html

The CDC's Division of Birth Defects, Child Development, and Disability and Health also provides information about autism on their web site, at: http://www.cdc.gov/ncbddd/dd/

For more information on vaccines and vaccine safety, contact the National Immunization Program (NIP) at 1-800-232-2522 (English) or 1-800-232-0233 (Spanish), or visit the NIP web site at http://www.cdc.gov/nip.

NIH, National Institute of Child Health and Human Development: http://www.nichd.nih.gov.