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by Nic Fleming
Far more children than previously thought have autism, according to research to be published today.
Researchers who studied 56,946 children in south London found that almost 0.4 per cent had "classic" childhood autism and just below 1.2 per cent had autism spectrum disorders (ASDs), including Asperger's and milder forms.
Until the 1990s, the generally accepted figure in Britain was four to five cases of autism per 10,000 - 10 times lower than the rate suggested in the new study.
More recently, estimates have put the prevalence of broad spectrum ASDs at around 60 children per 10,000.
Some campaigners have talked of an "autism epidemic", but experts differ on whether the increase is due to better diagnosis or a real growth in the proportion of children with the condition.
Prof Gillian Baird, of Guy's and St Thomas 's NHS Foundation Trust, London , examined rates of ASD in 56,946 children aged nine to 10 . Prof Baird and colleagues searched the special needs register for children with statements of special educational needs and records of those diagnosed as having social and communicative impairment. After screening the children identified, they concluded that there were 81 clear cases of autism and 77 cases of other ASDs.
This gave them a prevalence of 38.9 per 10,000 for autism, 77.2 per 100,000 for other ASDs and 116.1 per 10,000 for total ASDs.
ASDs cover a range of developmental disorders that impair the ability to interact socially and communicate. They cover a spectrum from severe cases of "classic" autism which could include an inability to talk, self-mutilation and mental retardation, through to milder forms including Asperger's.
Prof Baird, whose work is published in The Lancet, said: "Prevalence of autism and related ASDs is substantially higher than previously recognised." She added: "Services in health, education, and social care will need to recognise the needs of children with some form of ASD, who constitute one per cent of the child population."
Various theories have been put forward to explain the rising number autism diagnoses, including increased exposure to pesticides, pollution and childhood vaccination.
Some doctors are diagnosing children as autistic who would previously have been said to have attention deficit hyperactivity disorder (ADHD).