a1 MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, UK
a2 Rheinische Kliniken Essen Klinik für Psychiatrie und Psychotherapie des Kindes- und Jugendalters, Essen, Germany
a3 UZ – Gent De Pintelaan, Gent, Oos-Vlaanderen, Belgium
a4 Child and Adolescent Psychiatry, Georg-August-University, Goettingen, Germany
a5 ADHD Unit, Geha Mental Health Centre, Petach-Tikva, Israel
a6 Department of Child and Adolescent Psychiatry, University of Zurich, Switzerland
a7 Central Institute of Mental Health, Department of Child and Adolescent Psychiatry and Psychotherapy, Mannheim, Germany
Background Reaction time (RT) variability is one of the strongest findings to emerge in cognitive-experimental research of attention deficit hyperactivity disorder (ADHD). We set out to confirm the association between ADHD and slow and variable RTs and investigate the degree to which RT performance improves under fast event rate and incentives. Using a group familial correlation approach, we tested the hypothesis that there are shared familial effects on RT performance and ADHD.
Method A total of 144 ADHD combined-type probands, 125 siblings of the ADHD probands and 60 control participants, ages 6–18, performed a four-choice RT task with baseline and fast-incentive conditions.
Results ADHD was associated with slow and variable RTs, and with greater improvement in speed and RT variability from baseline to fast-incentive condition. RT performance showed shared familial influences with ADHD. Under the assumption that the familial effects represent genetic influences, the proportion of the phenotypic correlation due to shared familial influences was estimated as 60–70%.
Conclusions The data are inconsistent with models that consider RT variability as reflecting a stable cognitive deficit in ADHD, but instead emphasize the extent to which energetic or motivational factors can have a greater effect on RT performance in ADHD. The findings support the role of RT variability as an endophenotype mediating the link between genes and ADHD.
(Online publication May 31 2007)
c1 Address for correspondence: J. Kuntsi, Ph.D., MRC Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, De Crespigny Park (Box P080), London SE5 8AF, UK. (Email: J.Kuntsi@iop.kcl.ac.uk)