Harvard Mental Health Letter

Autism spectrum disorders

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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