Genes play a role in ADHD
Thursday 30 September 2010
Scientists at Cardiff University, supported by funding from the Medical Research Council (MRC), have found that children diagnosed with ADHD were more likely to have duplicate or missing segments in their DNA than other children without the condition. The research provides evidence in favour of attention-deficit/hyperactivity disorder (ADHD) having a genetic basis.
The study also found significant overlap between these DNA segments, known as copy number variants (CNVs), and genetic variants implicated in other neurodevelpmental disorders such as autism and schizophrenia. This does not mean that these conditions are the same, but does provide evidence that ADHD is a neurodevelopmental disorder. Rare CNVs were almost twice as common in children with ADHD compared to the control group – and even higher for children with learning difficulties.
The researchers, based at the MRC Centre for Neuropsychiactric Genetic and Genomics at Cardiff University, analysed the genomes of 366 children, all of whom had been given a clinical diagnosis of ADHD. They compared these against the genomes of over 1,000 control samples, in search of variations in their genetic make-up that were more common in children with ADHD.
Anita Thapar, Professor of Child and Adolescent Psychiatry at Cardiff University, led the study, said:
“We hope that these findings will help overcome the stigma associated with ADHD. Too often, people dismiss ADHD as being solely down to bad parenting or poor diet. Now we can say there is this class of genetic contribution to ADHD and that there are genetic similarities with autism and schizophrenia. There will be other types of genetic variation that also contribute as well as of course environmental influences"
Professor Chris Kennard, chair of the MRC Neuroscience and Mental Health Board, said:
“These valuable findings show how genes may play a role in conditions such as ADHD. The exact causes of ADHD are not yet known, but it’s clear that both genetic and environmental factors like diet and social circumstances are part of the puzzle. More research is needed to determine just how much influence genes have over other factors and we look forward to what future studies show.”
There were also similarities between CNVs identified in children with ADHD and regions of the genome which are known to influence susceptibility to autism and schizophrenia. These disorders are currently thought to be separate, but this new research suggests there may be a shared biological basis.
ADHD is one of the most common mental health disorders in childhood, affecting around one in 50 children in the UK. Children with ADHD are excessively restless, impulsive and distractible, and experience difficulties at home and in school. Although no cure exists for the condition, symptoms can be reduced by a combination of medication and behavioural therapy. The condition 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.
This finding does not in itself explain the cause of ADHD, nor will it be the major method for screening to find out in advance who might develop such behavioural problems. It is, however, a very important finding based on painstaking and rigorous research and yet another example of why genetic, psychological, neuropsychiataric and social studies need to proceed hand in hand.
The paper, Rare chromosomal deletions and duplications in attention-deficit hyperactivity disorder: a genome-wide analysis, published in The Lancet on 30 September and was funded by the Wellcome Trust, Action Medical Research, the Baily Thomas Charitable Trust, the Medical Research Council and the European Union.
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