Posted on: 15 December 2008
TCD collaborative research investigating the relationship between the genetics and psychology of children with and without Attention Deficit Hyperactivity Disorder (ADHD) has been judged by an international jury of the European Psychiatric Association as the best in Child & Adolescent Psychiatry in Europe in 2008. The research findings were published in the American Journal of Medical Genetics* this year.
ADHD affects between 3-5% of school-aged children in Ireland, with approximately 50% of these children continuing to suffer symptoms into adulthood. The research was funded by the Science Foundation of Ireland, the Health Research Board and the Programme for Research in Third-Level Institutions (PRTLI).
In carrying out the research, 128 children with and without ADHD were asked to perform a deliberately boring computer task, to see how often the children made mistakes and drifted off task. The children were grouped according to whether they possessed two copies or one/no copies of a genetic risk marker for ADHD located on a gene that codes for the neurotransmitter dopamine’s D4 receptor. Interestingly, the children with no copy of the risk marker and the clinical diagnosis of ADHD performed significantly more poorly on the task than the children with ADHD and at least one copy of the risk marker, but only on the elements of the task that reflected slow drifting attention.
On the measures that reflected moment-to-moment control of attention, there was no effect of the genetic marker, just a clinical group difference: children with ADHD performed more poorly than the typically developing children. These findings led the researchers to propose a new theory about the role of the dopamine D4 receptor in controlling the release of the neurotransmitter noradrenalin in the prefrontal cortex, the area of the brain heavily involved in attention. Noradrenalin is an important neurotransmitter involved in arousal. It is thought that children with ADHD have difficulties both in terms of maintaining attention to a task and with maintaining arousal levels, although not all children with ADHD will show these difficulties. This paper suggests that there may be a genetic basis to this variance.
The research team represents an excellent example of the collaborative nature of research at Trinity College Dublin. TCD researchers from Psychology (Dr Katherine Johnson, Professor Ian Robertson, Michael Daly), Psychiatry (Dr Edwina Barry, Dr Aisling Mulligan, Professor Michael Gill), Genetics (Dr David Lambert, Caroline McDonnell, Dr Ziarah Hawi) and Physiology (Dr Tom Connor) collaborated with researchers working in universities in the United States (Nathan Kline Institute – Dr Simon Kelly) and Australia (University of Queensland – Dr Mark Bellgrove).
Commenting on the significance of the research, lead author, Dr Katherine Johnson of TCD’s School of Psychology said: “Most children with ADHD will show difficulties in maintaining concentration on a task and this difficulty will become apparent quite quickly, say within the first minute of the task. Some children with ADHD also show a decline in performance on a task over a longer time period, say over a five minute period. This slower decline in performance appears to be related to a genetic marker for the dopamine D4 receptor. We proposed a novel hypothesis regarding the role of this receptor in relation to the neurotransmitter noradrenalin, which is involved in arousal levels”.
The prize money of €2,500 will be donated to two Irish local support groups for families with ADHD – ADHD Ireland (the North Fingal ADHD support group) (www.adhd.ie) and the Hyperactivity and Attention Deficit Disorder (HADD) family support group (www.hadd.ie).Anyone who is interested in participating in the research may contact Dr Katherine Johnson at [email protected].
Notes to Editor*The paper entitled: ‘Absence of the 7-repeat variant of DRD4 VNTR is associated with drifting sustained attention in children’ was published in the American Journal of Medical Genetics Part B (Neuropsychiatric Genetics) (2008)
