The behavior of children with the disorder can be explained by differences in the brain rather than parenting skills or diet, according to the study by scientists at Cardiff University.
The team found rare copy number variants - where small segments of DNA are duplicated or missing - were twice as common in children with ADHD than those without the condition.
According to the research, published in the Lancet, there was overlap between the affected parts of the DNA and those associated with autism and schizophrenia, The Press Association says.
Scientists at Cardiff University in Wales compared the DNA of 366 children with ADHD to that of 1,047 kids without the condition. They found that kids with ADHD were more likely to have small segments of DNA that were duplicates or missing.
"We hope that these findings will help overcome the stigma associated with ADHD," Professor Anita Thapar, the study's lead author, said in a written statement. "Too often, people dismiss ADHD as being down to bad parenting or poor diet.
As a clinician, it was clear to me that this was unlikely to be the case. Now we can say with confidence that ADHD is a genetic disease and that the brains of children with this condition develop differently to those of other children," CBS News reports.