4 October 2010

New evidence that ADHD is genetic

by Kate Melville

The results of genetic analysis of children with attention-deficit/hyperactivity disorder (ADHD) published in The Lancet reveal they were more likely to have small segments of their DNA duplicated or missing, lending new weight to the unfashionable theory that ADHD is a brain disorder with genetic links.

The study also found a significant overlap between these ADHD-related DNA segments and genetic variants implicated in autism and schizophrenia, providing strong evidence that ADHD is a neurodevelopmental disorder.

The Cardiff University researchers analyzed the genomes of 366 children, all of whom had been given a clinical diagnosis of ADHD, against over 1,000 control samples in search of variations in their genetic make-up that were more common in children with the condition.

"Children with ADHD have a significantly higher rate of missing or duplicated DNA segments compared to other children and we have seen a clear genetic link between these segments and other brain disorders," explains Dr Nigel Williams. "These findings give us tantalizing clues to the changes that can lead to ADHD."

The researchers found that rare copy number variants (CNVs) were almost twice as common in children with ADHD compared to the control sample - and even higher for children with learning difficulties. CNVs are particularly common in disorders of the brain.

There was also significant overlap between CNVs identified in children with ADHD and regions of the genome which are known to influence susceptibility to autism and schizophrenia. Whilst these disorders are currently thought to be entirely separate, there is some overlap between ADHD and autism in terms of symptoms and learning difficulties. This new research suggests there may be a shared biological basis.

The researchers also note that ADHD is highly heritable - children with ADHD are statistically more likely to also have a parent with the condition and a child with an identical twin with ADHD has a three in four chance of also having the condition.

"We hope that these findings will help overcome the stigma associated with ADHD," says Cardiff's Professor Anita Thapar. "Too often, people dismiss ADHD as being down to bad parenting or poor diet. 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."


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Source: Wellcome Trust