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Logo of behbrainBioMed CentralBiomed Central Web Sitesearchsubmit a manuscriptregisterthis articleBehavioral and Brain Functions : BBFJournal Front Page
 
Behav Brain Funct. 2008; 4: 4.
Published online Jan 30, 2008. doi:  10.1186/1744-9081-4-4
PMCID: PMC2267799
Relationship between endophenotype and phenotype in ADHD
Nanda NJ Rommelse,corresponding author1 Marieke E Altink,2 Neilson C Martin,3 Cathelijne JM Buschgens,2 Stephen V Faraone,4 Jan K Buitelaar,2 Joseph A Sergeant,1 and Jaap Oosterlaan1
1Department of Clinical Neuropsychology, VU University Amsterdam, Van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands
2Department of Psychiatry, Radboud University Nijmegen Medical Center, Reinier Postlaan 10, 6500 HB Nijmegen, The Netherlands
3School of Psychology, Curtin University of Technology, Kent Street, Bentley, Perth 6845, Western Australia
4Departments of Psychiatry and Neuroscience & Physiology, SUNY Upstate Medical University, 301 713 Harrison Street, Syracuse, NY 13210, USA
corresponding authorCorresponding author.
Nanda NJ Rommelse: nnj.rommelse/at/psy.vu.nl; Marieke E Altink: M.Altink/at/psy.umcn.nl; Neilson C Martin: n.martin/at/curtin.edu.au; Cathelijne JM Buschgens: c.buschgens/at/psy.umcn.nl; Stephen V Faraone: faraones/at/upstate.edu; Jan K Buitelaar: j.buitelaar/at/psy.umcn.nl; Joseph A Sergeant: ja.sergeant/at/psy.vu.nl; Jaap Oosterlaan: j.oosterlaan/at/psy.vu.nl
Received October 31, 2007; Accepted January 30, 2008.
Abstract
Background
It has been hypothesized that genetic and environmental factors relate to psychiatric disorders through the effect of intermediating, vulnerability traits called endophenotypes. The study had a threefold aim: to examine the predictive validity of an endophenotypic construct for the ADHD diagnosis, to test whether the magnitude of group differences at the endophenotypic and phenotypic level is comparable, and to investigate whether four factors (gender, age, IQ, rater bias) have an effect (moderation or mediation) on the relation between endophenotype and phenotype.
Methods
Ten neurocognitive tasks were administered to 143 children with ADHD, 68 non-affected siblings, and 120 control children (first-borns) and 132 children with ADHD, 78 non-affected siblings, and 113 controls (second-borns) (5 – 19 years). The task measures have been investigated previously for their endophenotypic viability and were combined to one component which was labeled 'the endophenotypic construct': one measure representative of endophenotypic functioning across several domains of functioning.
Results
The endophenotypic construct classified children with moderate accuracy (about 50% for each of the three groups). Non-affected children differed as much from controls at the endophenotypic as at the phenotypic level, but affected children displayed a more severe phenotype than endophenotype. Although a potentially moderating effect (age) and several mediating effects (gender, age, IQ) were found affecting the relation between endophenotypic construct and phenotype, none of the effects studied could account for the finding that affected children had a more severe phenotype than endophenotype.
Conclusion
Endophenotypic functioning is moderately predictive of the ADHD diagnosis, though findings suggest substantial overlap exists between endophenotypic functioning in the groups of affected children, non-affected siblings, and controls. Results suggest other factors may be crucial and aggravate the ADHD symptoms in affected children.
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