The Diagnostic and Statistical
Manual of Mental Disorders, Fourth Edition (DSM-IV)
describes five pervasive developmental disorders: autistic
disorder, childhood disintegrative disorder, Asperger's disorder,
Rett's disorder, and pervasive developmental disorder not otherwise
specified. Although they differ in some specifics, these disorders
share three core features: impaired social interactions, difficulty
in communicating with others, and repetitive or inflexible
behavior. Recognizing that these disorders differ mainly in terms
of severity, authors of the draft DSM-V, now undergoing review, have
proposed deleting Rett's disorder and including the other four
under the single category of autism spectrum disorder (ASD).
It remains unclear what causes an ASD, but most risk factors are
genetic. When one identical twin develops an ASD, then 82% to 92%
of the time the other one (who shares the same genes) will also
develop the disorder. The concordance rate drops to 10% or less in
fraternal twins, who share only some genes.
ASDs affect roughly one in 150 children, although some studies
suggest the prevalence may be higher. ASD diagnoses have been
increasing since the 1960s, but it remains unclear whether this is
because of better awareness and assessment, or some unknown
environmental factor that triggers these disorders in children who
are genetically susceptible.
There is no cure for any ASD, but early interventions — mainly
educational and psychosocial — take advantage of the developing
brain's ability to change in response to experience. As such, early
interventions may help improve a child's ability to communicate and
interact with others. An ongoing challenge, however, is making the
diagnosis as early as possible. In the United States, children are
4 to 5 years old, on average, when first diagnosed with an ASD,
even though parents generally express concerns about atypical
development much earlier, when children are 12 to 18 months old.
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