The prevalence of autism and related disorders was found to be “substantially greater” than expected in a screening of nearly 57,000 children in England.
The prevalence of autism spectrum disorders was 116 per 10,000 population. Previous estimates from research published in the past 6 years pegged the prevalence at only 30–90 cases per 10,000.
Before that, prevalence was widely accepted to be only four to five cases per 10,000, according to Dr. Gillian Baird, who is affiliated with Guy's and St. Thomas' NHS Foundation Trust, London, and her associates (Lancet 2006;368:210–15).
These findings indicate that autism spectrum disorders are not the rare anomalies that the public has always considered them to be but instead affect about 1% of children aged 9–10 years, they added.
In an editorial comment accompanying their report, Dr. Hiroshi Kurita of Zenkoku Ryoiku Sodan Centre, Tokyo, speculated that the recent surge in prevalence is more likely attributable to improved case ascertainment rather than to a true increase in the disorders (Lancet 2006;368:179–81).
Dr. Baird and her associates screened a population cohort of 56,946 children born 1990–1991 in 12 districts in South Thames, England.
The subjects were aged 9–10 years at assessment, “an age when it is likely that all true cases of autism spectrum disorders, or at least those in whom the condition was causing significant functional impairment, would have come to the attention of health and education services.”
They used data from the special needs register of the department of child health services to identify those who might have an autism spectrum disorder.
The registry also listed all children who attended special schools or mainstream schools and whose files contained a statement of educational needs indicating they had language, learning, behavior, or medical problems requiring intervention.
The researchers also collaborated with local clinicians to search registers of children known to various therapy services for having social or communicative impairment or autism spectrum disorders.
In all, they identified 255 children with a current diagnosis of autism spectrum disorders and another 1,515 considered to be potential candidates for the diagnosis.
The investigators screened these subjects using a parent-report questionnaire on characteristic autistic behavior. They then conducted detailed clinical assessments of a random sample of 255 subjects (223 boys, 32 girls). This included in-person observation and scoring on two diagnostic tools, the autism diagnostic interview-revised (ADI-R) and the autism diagnostic observation schedule-generic (ADOS-G); it also included review of teacher reports, psychometric testing results, and other extensive case material.
Based on these results, Dr. Baird and her associates estimated the prevalence of autism spectrum disorders to be 116 per 10,000 population.
When the data were broken down into subtypes, the prevalence of narrowly defined autism was 39 per 10,000, and the prevalence of other pervasive developmental disorders was 77 per 10,000.
The National Autistic Society, the leading charity for people with autism spectrum disorders in the United Kingdom, says there are about 520,000 people with autism spectrum disorders in the U.K.
Mounting evidence shows that genetic factors may play a prominent role in the causes of autism spectrum disorders. In addition, twin studies have suggested a genetic vulnerability to ASD. The disorders can be diagnosed in young toddlers and even in infants. But screening advances have not yet filtered to clinical practice.
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