Researchers find genetic clues to ADHD

Parents frustrated at claims that attention deficit hyperactivity disorder (ADHD) is the result of poor diet and / or bad parenting may take some solace this week after researchers published a study showing for the first time that the brains of children with the condition are different to those without it.

Scientists at Cardiff University in Wales analysed the genomes of 366 children given a clinical diagnosis of ADHD against more than 1000 control samples in the hopes of revealing genetic variations. What they discovered is that the children diagnosed with the condition were much more likely to have small segments of their DNA either duplicated or missing.

These segments, known as copy number variants (CNVs), are particularly common in disorders of the brain. The researchers found that rare CNVs were almost twice as common in children with ADHD compared to the control sample, while children diagnosed with learning difficulties had even more of them.

"We hope that these findings will help overcome the stigma associated with ADHD," says Cardiff University’s Professor Anita Thapar, who led the study. "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."

The researchers also identified a number of overlaps with genetic variants connected with both autism and schizophrenia. One CNV overlap which the researchers found especially interesting is located on a particular region of chromosome 16, which previous studies have linked to serious psychiatric disorders including schizophrenia, while it also spans a number of genes including one which is known to be involved in the development of the brain.

The apparent biological similarities between ADHD and autism revealed by the study are also significant given the similar symptoms of the two conditions.

"These findings are testament to the perseverance of Professor Thapar and colleagues to prove the often unfashionable theory that ADHD is a brain disorder with genetic links,” said Dr John Williams, Head of Neuroscience and Mental Health at the Wellcome Trust which has supported the work for past 10 years. “Using leading-edge technology, they have begun to shed light on the causes of what is a complex and often distressing disorder for both the children and their families."

The study, which also drew assistance from Action Medical Research, the Medical Research Council and the European Union, is published the latest edition of The Lancet.