Research has indicated that attention-deficit hyperactivity disorder is a genetic condition.
A study completed by Cardiff University scientists linked the disorder with differences in the brain rather than parenting skills or diets.
Around one in 50 UK children is affected by ADHD, making them restless, fidgety, impulsive and easily distracted. This can lead to problems for them at school.
The Cardiff team discovered that rare copy number variants, where DNA segments are either duplicated or missing, were twice as common among ADHD children than those without the condition.
The new research, which has been published in the Lancet, revealed an overlap between affected DNA segments and chromosomes that have been linked with autism and schizophrenia in the past.
Researchers drew particular attention to a region on chromosome 16, which has already been associated with a host of psychiatric disorders and contains genes that can affect the development of the brain.
Despite children being statistically more likely to have ADHD if one of their parents has it, there had been no direct evidence before this study to show it was a genetic disorder.
Professor Anita Thapar, from Cardiff’s Department of Psychological Medicine and Neurology, said: “We hope that these findings will help overcome the stigma associated with ADHD.”