The number of children with autism has risen 12-fold in the past 30 years and may be 50 per cent higher than previously suspected, the most detailed study of the condition yet has found.
Up to 250,000 children have autism or a related condition on the autistic spectrum, but have not been diagnosed, researchers say. They are in addition to the 500,000 children who are known to be affected.
The authoritative study by Professor Simon Baron-Cohen and colleagues of the Autism Research Centre at Cambridge University, published in the British Journal of Psychiatry, sets a new benchmark for future studies of the prevalence of autism in the UK, and has grave implications for education and other public services which are already overstretched. The findings imply that many more young people may need intensive lifelong support.
But the authors dismissed suggestions that changes in lifestyle or the environment were behind the rise. They put it down to improved awareness and detection, and the inclusion of milder conditions within the diagnosis.
Autism is a disorder of social functioning which makes it difficult for sufferers to form relationships and to communicate with other people. In the 1990s it was recognised that there was a spectrum of cases from the severely to the mildly affected, and the diagnosis of Asperger's syndrome was included to cover those at the milder end.
Autism has become controversial over the last 10 years because of a claimed link with the MMR vaccine, which has since been discredited. The rise in cases was cited by campaigners as evidence for the damaging effects of MMR, which was introduced in 1988.
In 2006, researchers from Guy's and St Thomas' medical school calculated that 1 per cent of the population had a diagnosis on the autistic spectrum, equivalent to 500,000 children. That figure has become the gold standard in autism research.
Now Professor Baron-Cohen has revised the figure, using three separate research methods for increased accuracy on a population of 20,000 children in Cambridgeshire.
A survey of Cambridge school registers of children with special educational needs revealed 1 per cent of children affected. This was confirmed by a questionnaire survey of parents which uncovered 41 cases. But a subsequent screening test given to the same parents, designed to detect children with autism, revealed an additional 11 children who were undiagnosed.
The results showed that, when the undiagnosed cases were included, one in 64 children had the condition, equivalent to 1.5 per cent of the population. Extrapolating them to the whole population raised the total number of children affected from 500,000 to 750,000. For every three cases that are diagnosed, a further two may be undiagnosed, the researchers concluded.
Professor Baron-Cohen said: "If services are trying to plan ahead they have to take into account that for every three cases they know about there may be two more they don't. That is important. Currently many services are stretched, they are barely managing to keep up and there are long waits for diagnosis."
He added: "Not everyone may need a diagnosis if they are already getting good support. But services need to be prepared. People usually seek a diagnosis when things start to go wrong, for example when they leave home and are losing the support of parents."
The National Autistic Society said early diagnosis was essential. Parents often wait years for accurate diagnosis. Mark Lever, NAS Chief Executive, said: "An accurate figure for the number of people with autism... is vital to ensure a sufficient level of services and appropriate support to meet people's needs."
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