PARIS • People with attention deficit hyperactivity disorder (ADHD) have slightly smaller brains than those without the condition, according to a study released yesterday, which said it is a physical disorder and not just bad behaviour.
The largest analysis to date of the brains of people with ADHD found "structural differences", as well as evidence of delayed development compared with people without the condition, researchers reported.
"The results from our study confirm that people with ADHD have differences in their brain structure and therefore suggest that ADHD is a disorder of the brain," said the lead author, Dr Martine Hoogman from the Netherlands' Radboud University Medical Centre.
"We hope that this will help to reduce stigma that ADHD is 'just a label' for difficult children or caused by poor parenting."
The results of the study, which involved 1,713 people with ADHD and 1,529 people without, were published in The Lancet Psychiatry.
Most often diagnosed in children, ADHD is blamed for severe and repeated bouts of inattention, hyperactivity or impulsiveness that can cause problems at school or home.
The symptoms can persist into adulthood.
The causes remain in dispute, and some specialists say ADHD is nothing but an excuse for using drugs to subdue children with difficult personalities or bad parents.
Drugs for treating ADHD, such as Ritalin, have been blamed for side effects that include weight loss or gain, liver damage and suicidal thoughts.
In the study, Dr Hoogman's team analysed the MRI scans of people aged four to 63, both with and without ADHD. They measured overall brain volume, as well as the size of seven brain regions thought to be linked to the disorder.
The overall volume was smaller in people diagnosed with ADHD, as were five of the brain regions, the team said.
"These differences are very small - in the range of a few per cent - so the unprecedented size of our study was crucial to help identify these," Dr Hoogman said.
"Similar differences in brain volume are also seen in other psychiatric disorders, especially major depressive disorder."
The regions affected included the amygdala, which is involved in the regulation of emotion.
Previous studies which associated changes in brain volume with ADHD had been too small to be conclusive, the team said.
The differences observed in their study were most prominent in children, but were also present in adults with the condition.
The findings suggest that delays in the development of several brain regions are characteristic of ADHD, the researchers said.