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ADHD genetics is a complex issue, say experts

04 October 2010

By Chris Chatterton and Rose Palmer

Appeared in BioNews 578

Last week researchers from Cardiff University published a study in the Lancet, where they claimed to have uncovered evidence of a genetic link to attention deficit hyperactivity disorder (ADHD), and suggested that this proved that the condition was 'not purely a social construct'.

ADHD is described as a neurodevelopmental disorder, characterised by hyperactivity (an unusually or agitated state of mind) and difficulty in paying or sustaining attention, which is estimated to affect at least two per cent of children.

The researchers conducted a genome-wide association study (GWAS) and compared the DNA of 366 children with ADHD with a control group of 1156 individuals.

They were particularly interested in looking for CNVs (copy number variants), which are rare chromosomal deletions and duplications, because these have previously been linked to other disorders such as schizophrenia and autism.

They identified 57 large rare CNVs amongst the 366 children with ADHD and 78 amongst the 1156 individuals in the control group, which showed that these CNVs were significantly more common in individuals with ADHD.

The study also found that the rate was high amongst those individuals with intellectual disability, but that the level was also significant in those with no such disability.

These findings offer clues to the probable genetic underpinnings of ADHD, but the current study is not able to give scientists any definitive answers as to their exact role in the disorder and should be greeted with interest, but not as indicative of causation.

Unfortunately, this research was reported by many media sources as proving that ADHD was fundamentally a 'genetic condition'.

This sparked a much wider debate as to the origins of ADHD, and the extent to which the condition is a result of nature or nurture, and whether parents should be blamed for their child's behaviour.

Experts on both sides of the debate greeted the press coverage and original paper with excitement.

Professor Anita Thapar, an expert in child and adolescent psychiatry, said: 'This is really exciting because it gives us the first direct genetic link to ADHD'. She added: '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.

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

However, other experts remain unconvinced. Dr Tim Kendall, a consultant psychiatrist and expert on ADHD, said labelling the disorder as biological could encourage physicians to treat the disorder with a biological answer.

'I am saying it's a mixture of genetic and environmental factors, and the important thing is that we don't end up thinking this is a biological problem which is only subject to biological treatments like Ritalin'.

Oliver James, the psychologist and author, also attacked the researchers for putting 'massive spin' on their findings, pointing out that only 57 of the 366 children with ADHD in the study had the gene variant supposed to cause the disorder.

The challenge for scientists in the future is to untangle the interaction between genes and the environment in order to develop more effective treatments for the disorder.

 

SOURCES & REFERENCES
The Telegraph | 30 September 2010
 
BBC News | 30 September 2010
 
New Scientist | 30 September 2010
 
The Lancet | 30 September 2010
 
BBC | 30 September 2010
 

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