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In 1943 Leo Kanner, a child psychiatrist, described a group of children with extreme aloofness and “total indifference” to other children, which he labeled autistic disturbances of affective contact. His description is as relevant today as it was back then: “The children use (language) for the purpose of communication. . When sentences are formed, they are for a long time mostly parrot-like repetitions of heard word combinations. They are sometimes echoed immediately. .” “There is a limitation in the variety of his spontaneous activities. . The dread of change and incompleteness seems to be a major factor in the explanation of the monotonous repetitiousness and the resulting variety of spontaneous activity.”1 Hans Asperger independently described children who demonstrated symptoms similar to Kanner’s patients but had higher cognitive and verbal skills. The conceptualization of this disorder has since broadened, and the most recent version of the Diagnostic and Statistical Manual of Mental Disorders2 describes pervasive developmental disorders (PDDs). These include 3 autism spectrum disorders (ASDs): autistic disorder, Asperger disorder, and pervasive developmental disorder not otherwise specified (PDD-NOS). Two other diagnoses, Rett syndrome and childhood disintegrative disorder are also included in the DSM-IV-TR but are not considered ASDs.

Current estimates of the prevalence of autism are 1 in 150 or 6.6 per 1000 8-year-olds.3,4 This accounts for 1 to 1.5 million children in the United States, a 10-fold increase from older studies. The older studies of autism prevalence targeted autism disorder alone, while the newer studies also include individuals with Asperger disorder and PDD-NOS. From a public health perspective, this amounts to a cost of over $90 billion annually, 90% of which is attributable to the cost of adult services.5

The increase in prevalence of autism represents, in part, the broadening of autism spectrum disorder (ASD) diagnostic categories in the DSM, increased public awareness, more reliable screening and evaluation tools, increased physician awareness, better ascertainment of cases, the introduction of a school designation of an educational category of ASD, and the eligibility of children with ASDs to receive special education services under the Individuals with Disabilities Education Act (IDEA).6 This may also reflect increased ascertainment of children with milder ASDs, including higher functioning children. For example, the rate of mental retardation (IQ < 70 with commensurate levels of adaptive functioning) associated with ASDs has gone from 90% in the 1990s to less than 50% in 2000. Diagnostic substitution may also play a role. The number of children receiving special education services under categories such as mental retardation language, language disorders, and learning disabilities has decreased over the same period that the diagnosis of autism has increased. The impact of this process is still considered controversial.

Public concern about whether the increase in prevalence is in part due to receiving the measles-mumps-rubella (MMR) vaccine and/or to the preservative thimerosal mercury in vaccines has led to an extensive public debate. As a recent Web ...

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