SONUGA-BARKE, E. J. S., Brookes, K-J., Buitelaar, J., Anney, R. J. L., Bitsakou, P., Baeyens, D., Buschgens, C., Chen, W., Christiansen, H., Eisenberg, J., Kuntsi, J. Manor, I., Melia, A., Mulligan, A., Rommelse, N. N. J., Müller, U. C., Uebel, H., Banaschewski, T., Ebstein, R., Franke, B., Gill, M., Miranda,A., Oades, R. D., Roeyers, H., Rothenberger, A., Sergeant, J. A., Steinhausen, H-C., Thompson, M., Taylor, E. A., Asherson, P. & Faraone, S.V.
Intelligence in DSM-IV combined type attention-deficit/hyperactivity disorder is not predicted by either dopamine receptor/transporter genes or any other previously identified risk alleles for attention-deficit/hyperactivity disorder. American Journal of Medical Genetics, part B, 147, 316-319. doi 10.1002/ajmg.b.30596 (Request a Copy): View Article

Introduction : A major goal of genetic studies of ADHD is to identify individual characteristics that might help segregate the disorder's inherent heterogeneity. a) Mill et al. 2006 recently reported a potentially-important association between 2 dopaminergic (DA) risk polymorphisms (DRD4 7 repeat & DAT1 10/10) & lowered IQ in ADHD. b) We aimed to replicate the Mill et al. findings in a clinical sample & to extend the analysis to a large range of alternative SNP (single nucleotide polymorphism) markers of putative ADHD risk alleles identified in a recent study (Brookes et al. 2006).

Methods : We examined the association of allelic risk & IQ within a large clinically ascertained sample in multiple settings across Europe: Belgium, Britain, Germany, Ireland, Israel, Netherlands, Spain, Switzerland. Particpants were 1081 children & adolescents with a research-confirmed combined type ADHD diagnosis & 1300 unaffected siblings - with a clinical assessment of ADHD & IQ.

Results :

1/ ADHD was associated with reduced IQ.

2/ There was no association between the 2 DA genotypic risks (D4 & DA transporter) & IQ in either the probands or their siblings.

3/ Furthermore, other selected genetic markers previously demonstrated to be associated with ADHD in this sample were not associated with IQ.

Conclusions : - [I] - This large scale study with a clinically ascertained & rigorously diagnosed sample failed to replicate the association between genetic polymorphisms in the DA system & IQ in ADHD.- [II] - We also observed no associations of other SNPs with IQ in ADHD.

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