Researchers from Cardiff University found that children with ADHD are more likely to have some of their DNA duplicated or missing, which they said was proof that ADHD, like autism and schizophrenia, is a neurodevelopmental disorder.
Lead author Anita Thapar, professor of child and adolescent psychiatry at the university's School of Medicine, said, 'Too often people dismiss ADHD as being down to bad parenting or poor diet. Now we can say with confidence that the condition is a genetic disease and the brains of children with ADHD develop differently to those of other children.'
The researchers analysed the genetic make-up of 366 children aged five to 17 with ADHD against 1,000 control samples from the 1985 British Birth Cohort to look for variations common in children with the condition.
They found that a rare segment of DNA named copy number variants (CNVs), which are commonly associated with disorders of the brain, were almost twice as common in children with ADHD compared with the control sample, and even higher in children with learning difficulties.
The findings also showed that there may be a shared biological link to ADHD and autism along with the similarities in symptoms and learning difficulties.
John Williams, head of neuroscience and mental health at the Wellcome Trust said, 'This study has begun to shed light on the causes of what is a complex and often distressing disorder for both the children and their families.'
'Rare chromosomal deletions and duplications in attention-deficit hyperactivity disorder: a genome-wide analysis' is published in last week's issue of The Lancet.