CHILDREN with attention deficit hyperactivity disorder, the controversial “bad behaviour” syndrome, are suffering from a medical condition linked to abnormal development of the brain, scientists said yesterday.

Brain scans of children with the disorder — which some critics allege has been invented or exaggerated by drug companies seeking lucrative markets — have revealed a common pattern of changes, providing evidence that ADHD is a genuine biological phenomenon.

According to studies, its origins are largely genetic and it is not the result of poor parenting. Growing up in a “chaotic environment”, to which parents with poor skills can contribute, may trigger the condition among children who are already genetically susceptible. The condition, which involves restlessness, impulsive behaviour and a short attention span, is thought to affect up to one in twenty British children, with about a quarter of these suffering from a more severe form, hyperkinetic disorder. The condition is more common among boys than girls.

Increasing rates of diagnosis have alarmed some researchers and parents’ groups, with doctors and pharmaceutical companies being accused of “medicalising” ordinary disruptive behaviour. They fear that many children, including teenagers, are being treated with powerful drugs such as Ritalin that they do not need.

But, according to Professor Eric Taylor, of the Institute of Psychiatry, in London, the latest research suggests that too few children with the disorder are receiving the help that they need.

Professor Taylor’s review of 17 brain scan studies involving about 350 children has identified common features.

Several regions that are involved in self-control and inhibiting impulsive behaviour — the right frontal lobes, the basal ganglia and the vermis of the cerebellum — are appreciably smaller in ADHD patients.

Children who have ADHD are four times more likely to have mental health problems when they reach adulthood, and the condition gets worse if it is not treated.

“This work shows that there is a distinction between ordinary bad behaviour and ADHD,” Professor Taylor told the British Association Festival of Science at the University of Exeter.

“Parents and families are right in saying that it starts with a physical influence, and it should be thought of as a long-term subtle disability. A proportion of the population are suffering from a real but somewhat invisible disability.”

An estimated 250,000 British children may suffer from ADHD. It is often undiagnosed. Hyperkinetic disorder affects 1.4 per cent of children. Professor Taylor said that drug treatment was recommended to treat hyperkinetic disorder.

His team has recently followed up hundreds of boys who had ADHD diagnosed at the age of seven to determine their long-term progress, and found a fourfold increase in rates of mental illness in adulthood. The risks were higher for those who were not treated with drugs.

He said: “The main thing that says it’s not a fiction of the drug firms is that if you don’t treat it it gets worse.”

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