Autism may be linked to children watching television when very young, according to researchers.
Scientists investigating the dramatic increase in the number of autistic children have said the rise coincided with the use of cable television and videos. Autism is at record levels in the UK, where one in 110 people - more than half a million - has the condition, according to the National Autistic Society.
Researchers investigating autism in the US said that, as recently as 30 years ago, it was thought one in 2,500 people had the condition. Today the figure is one in 166, a 15-fold increase.
Scientists wanted to investigate whether the early introduction of cable television in the US had contributed to the current generation of children with autistic-spectrum symptoms. Researchers at Cornell University said children prone to autism might go on to show symptoms because of environmental triggers. Watching television could be one of them.
Michael Waldman and Sean Nicholson from Cornell University said autistic children usually develop the condition by the age of three. Their research, conducted across California, Oregon and Washington states, set out to prove the theory by linking the amount of television a child watches with the number of days when it rained.
The researchers said their study showed just under 40 per cent of autism diagnoses could be explained by looking at the times when children were forced to stay in and watch television. When rainfall was high, autism rates rose sharply. The opposite was true when rainfall was low.
They did not say how watching TV could act as a trigger, but simply tried to show a relationship. Research has shown, however, that autistic children have unusual activity in parts of the brain that process visual information. These areas develop in the early years.
The Cornell study looked at the results of an investigation into the Amish community. Based on the autism rates across the US, there should be several hundred autistic Amish, but fewer than 10 were found.
Health scares in the UK linked the combined MMR vaccine with autism but scientific studies have failed to find a connection.
Carol Povey, head of adult services for the National Autistic Society, saidit had an open mind on whether autism was rising. "The causes of autism are still being investigated," she said.
The findings are likely to upset parents of autistic children. Deborah Packenham, 42, from London, whose son Ieuan, eight, is autistic, said: "I think the idea that television is an environmental trigger for autism is difficult to grasp, dangerous even... it risks parents beating themselves up for letting their children watch Teletubbies when they were younger."
WHAT IS AUTISM?
A range of symptoms, including difficultiesforming relationships and communicating. Sufferers can be obsessed with a narrow range of interests and do or say things repetitively. Asperger syndrome shares some of the symptoms, but sufferers often have average or above-average IQs.
MYTHS AND FACTS
Myth: Autism (including Asperger syndrome) is rare.
Fact: Autism (including Asperger syndrome) is thought to affect about 535,000 people in the UK.
Myth: People with autism have extraordinary abilities.
Fact: Sufferers with extraordinary gifts are called autistic savants. Between 2 and 3 per cent of the UK's population have a learning disability, but only a tiny number of these have an unusually high level of specific talent.
Myth: Asperger syndrome is a middle-class sickness made up by parents to excuse bad behaviour.
Fact: Asperger syndrome is a real condition. It is often spotted at around 11-13 years of age, and its effects can be devastating.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies