Attention deficit hyperactivity disorder (ADHD) is one of the most prevalent, stable and heritable disorders of childhood. It is also one of the commonest causes of referral to child mental health services. Whereas ADHD is a clinical diagnosis, all children show the key characteristics - overactive, impulsive and inattentive behaviours - to varying degrees. In the SAIL project we investigate these behaviours in children representative of the general population.
Sail (Study Of Activity And Impulsivity Levels In Children)
(Funded by The Wellcome Trust)
Jonna Kuntsi Click Here, Philip Asherson Click Here
By combining cognitive-experimental and genetic methods, the project aims to identify psychological processes that mediate the genetic influences on ADHD behaviours. A sample of 800 twin pairs are recruited from the large TEDS study. We measure the performance of each individual twin on theory-driven experimental tasks that have been associated with ADHD or which tap into reward-related processes. We also gather behavioural measures of ADHD symptoms and novelty seeking. To enable molecular genetic analyses, we collect DNA samples from the twins and their parents. In an initial stage of the project we have carried out a test-retest reliability study in schools for tasks in the test battery.
The twin design enables an investigation of the extent of genetic effects on performance on the experimental tasks and whether these are shared with the genetic effects on ADHD behaviours. We will test the further hypotheses that genetic variation in monoamine pathway genes is associated with the key psychological processes, and that the effects of these processes extend to related behaviours such as novelty seeking.
The SAIL project is closely linked to the IMAGE project, which focuses on a sibling sample of children with clinically diagnosed ADHD. By administering key tasks from the cognitive-experimental test battery in both studies, we can test the genetic mediation hypothesis in relation to both ADHD diagnosis and ADHD behaviours in the general population. This enables an empirical test of the hypothesis that ADHD represents the extreme of a quantitative trait.