It has been suggested that the symptoms of ADHD (inattention and/or hyperactivity/impulsivity), translate into deficits in task-oriented behaviour or problem-focussed activity. The fronto-subcortical dopamine and norepinephrine pathways have been implicated in ADHD, and one of the key modulators of these neurotransmitters in the prefrontal cortex is catechol-O-methyltransferase (COMT).
To examine the association of the COMT Val108/158Met polymorphism with (1) task-oriented behaviour in children with ADHD, and (2) response of this phenotype to methylphenidate treatment.
Design, Setting, Participants
Children diagnosed with ADHD (n=212), were assessed using the Restricted Academic Situation Scale (RASS). The RASS uses a simulated academic environment within the research clinic, to assess the child's ability for independent, sustained orientation to a task of math problems.
Each child was administered placebo and methylphenidate (0.5 mg/kg in a divided b.i.d. dose), each for a one-week period, in a double-blind, crossover trial. On day 3 of the respective treatment week, the child was administered placebo/ methylphenidate in the clinic, and the acute change in behaviour (before and 1 hour after treatment) was evaluated on the RASS.
Main Outcome Measure
The main outcome measure was the RASS score (number of behavioural events measured during a 15-minute time period), measured at four time points: before and after placebo/methylphenidate treatment. Analysis was carried out using mixed model analysis of variance.
Significant main effects of COMT genotype [F2,206 = 4.78, p = 0.009] and treatment [F1,206 = 45.22, p < 0.0001] on task-oriented behaviour were observed. The Met-Met and Val-Met genotype groups had fewer behavioural events, and were more engaged in the math task, compared to the Val-Val group. No genotype by treatment interaction was observed.
These results suggest that the COMT Val108/158Met polymorphism modulates task-oriented behaviour, but it does not modulate the response of this behaviour to MPH treatment.