Autism is commonly regarded as being much more common in boys than in girls, but this may reflect differences in the way the disorder affects the female brain, according to Chris Gillberg, of the National Centre for Autism Studies at the University of Strathclyde.

Between three and four times as many boys as girls are generally diagnosed with autism, a condition that produces problems in communication and social interaction. Previous studies have suggested that autism is up to 14 times more common in males.

Professor Gillberg, however, said that the gap between the sexes is closing with more research, which suggests that the extent of the condition in females may have been underestimated. Girls, he said, may be less likely to have autism diagnosed because they tend to be less outgoing than boys, making social difficulties and other autistic traits harder to detect. The condition may manifest itself in other disorders, such as anorexia.

Professor Gillberg said: “Autism may be behind many cases of anorexia. A girl may be withdrawn and uncommunicative without attracting attention, but when she develops a calorie fixation, it becomes a serious problem. Counting calories may be a manifestation of autism.

“Some women could be going undiagnosed. It could be that the current idea that three to four times more males have autism than females is an inflation of the reality.”

Professor Gillberg, speaking at the launch of the British affiliate of the National Alliance for Autism Research (NAAR), a charity that operates in the United States, said that the condition probably does have a male bias, but that it is more likely to be two to three times more common in males than in females. Many other behavioural conditions, such as attention deficit hyperactivity disorder, are also more common in boys, he said.

Other leading autism researchers attending the NAAR gathering said that the rising incidence of the condition probably does not represent an epidemic; rather, it is more likely to reflect better diagnosis and awareness.

Autism was once considered to be a rare condition that was diagnosed in as few as two people in 10,000, but its incidence is recognised to be as high as 60 in 10,000 — or about 535,000 people in Britain.

Professor Gillberg and other scientists said that the best explanation for this is improved diagnosis and parental familiarity with the disorder.

Tony Charman, of the Institute of Child Health at University College London, said: “There is no clear evidence that there has been an actual increase. A broadening of understanding of what autism is as a condition is likely to account for all the rise of prevalence.”

Simon Baron-Cohen, of the Autism Research Centre at the University of Cambridge, said that parental awareness of autism is crucial. He said: “In every town you can now go to a child-development centre with trained specialists who can diagnose the condition. Ten or twenty years ago, there was just a small number of hospitals with that capacity.”

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