IntroductionGinny Russell looks at new research claiming a genetic link with ADHD.
Research published in The Lancet linking Attention Deficit Hyperactivity Disorder (ADHD) to genetic variation provoked widespread media coverage (writes Egenis researcher Ginny Russell). The researchers from the University of Cardiff compared the DNA of 366 children with symptoms of attention deficit hyperactivity disorder and 1,047 control subjects not known to have the condition. They found that 14 per cent of children with ADHD had large, rare variations in their DNA that were present in only 7 per cent of controls. This case-control study looked at whether large deletions and duplications within DNA (called copy number variants or CNVs) might be more common in people with ADHD. Rare CNVs have been found to be associated with conditions such as autism, intellectual disability and schizophrenia, so the researchers wanted to determine whether they might also be associated with ADHD. They were particularly interested in whether ADHD, autism and schizophrenia might all be linked to specific CNVs.
The researchers found that large CNVs were more common in children with ADHD than in controls. They identified 57 large, rare CNVs in children with ADHD and 78 in controls. The average number of CNVs in each individual was about twice as high in cases as in controls, with an average of 0.156 CNVs per child with ADHD and 0.075 CNVs per control. Large CNVs were present in 14 per cent of the children with ADHD and in 7 per cent of controls. The authors concluded that these results demonstrate that ADHD is not purely socially constructed. A more accurate appraisal of their work would be that it provides evidence that there may be an association between ADHD type behaviours and this particular type of genetic variation. What renders these particular behaviours into a childhood ‘disorder’ is constructed. ADHD is not simply a description of behaviour: it is a diagnostic category that defines which behaviours are considered abnormal. The diagnostic classification schemes for childhood disorders are rooted in their social and historical context. In other words, the study shows a association between genetic factors and hyperactive behaviours, but a further construction is required for such behaviours to be considered a ‘disorder’.
Wydell and Butterworth (Wydell, T.N. and Butterworth, B., 'A case study of an English-Japanese bilingual with monolingual dyslexia', Cognition 1999, 70, 273-305) illustrate how difficulties become apparent in different contexts, citing the case of a boy bilingual in English and Japanese whose dyslexic difficulties only related to English. This illustrates how the background circumstance can lead to the manifestation of a difficulty. There is a fishing village in India where boys are encouraged to work on their father’s boats. In this situation, a boy who is bounding with energy and unable to sit, in other words, who reaches diagnostic thresholds for ADHD, might be an asset if constant physical activity is required. Children in UK classrooms, by contrast, are expected to sit still and concentrate on tasks they may find difficult. In this sense, attention deficit behaviours are rendered apparent as difficulties by their context.
The recent Cambridge Primary Review concluded that the school system could be damaging a small proportion of children because they are moved to formal education before they are ready to learn in this way, which might prove counter-productive. A more immediately applicable piece of research could be to determine if there is an association between this minority of children whom the system is failing and the symptoms of ADHD, and if so, whether starting formal education later would help halt the development of these incapacitating symptoms.