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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.
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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
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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.
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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 site posting proclaims: “Take
one preventive medicine that everyone gets, and one devastating
disease that no one understands. Mix them together, add a provocative theory,
and you have a recipe for a public health disaster.”7 In
2004, the Institute of Medicine of the American Academy of Science
conducted an extensive study and concluded that evidence does not
support a causal relationship between MMR or thimerosal mercury
and autism.8 They found that ...