Wood, A.C., Rijsdijk, F., Andreou, P., Christiansen, H., Gabriels, I., Marco, R., Meidad, S., Mueller, U., Mulligan, A., Uebel, H., van der Meere, J.J., Banaschewski, T., Gill, M., Manor, I., Miranda, A., Mulas, F., Oades, R.D., Roeyers, H., Rothenberger, A., Steinhausen H-C., Faraone, S.V., Asherson, P., & Kuntsi, J.

Familial factors underlying ADHD and cognitive task performances. 2nd International Congress on ADHD, 21 - 24 May 2009, Vienna, Austria

Introduction: ADHD is associated with poor performance across a range of cognitive tasks. Yet the extent to which the apparent cognitive and energetic deficits share a common or independent etiology is unknown. We aimed to study the architecture of the familial influences underlying ADHD and five measures of task performance: mean reaction time (MRT), reaction time variability (RTV), commission errors (CE), omission errors (OE) and choice impulsivity (CI). .

Methods: Multivariate structural equation modelling was used on cognitive task data from a large international multi-centre sample of ADHD and control sibling pairs, at ages 6-18. Task data were regressed for age, sex and IQ. A confirmatory factor analysis decomposed the variance in measures into shared and unique (or residual) familial and environmental effects.

Results:
1 - All measures of cognitive performance showed a significant phenotypic correlation with ADHD after controlling for the effect of IQ (MRT: r=.32; RTV: r=.36; CE: r=.17; OE: r=.25; CI: r=-.12).

2 - Two main familial factors emerged, accounting for 83% of the variance in ADHD diagnosis.

3 - The first factor explained almost all the familial variance between MRT (100%) and RTV (99%), and the majority of the ADHD familial variance (68%).

4 - The second factor accounted for all of the familial variance underlying CE (100%) and about half that of OE (53%).

5 - The familial variance in CI showed a low loading onto either of these factors (0% to error factor; 18% to the RT factor).

Discussion: ADHD shows the strongest phenotypic and familial association with reaction time performance (MRT and RTV). This association is largely independent of the familial association between ADHD and error variables (CE and OE). These findings on the familial architecture underlying the association between ADHD and cognitive performance will inform future molecular genetic investigations.