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Deficient response inhibition as a cognitive endophenotype of ADHD
Dorine Slaats-Willemse1, Hanna Swaab-Barneveld, Leo de Sonneville
1Department of Child and Adolescent Psychiatry, University Medical Center, Huispostnr: F05.126, P.O. Box 85500, 3508 GA Utrecht, The Netherlands. d.willemse@psych.azu.nl
Objective:
To investigate whether a deficient response inhibition is a cognitive endophenotype of attention-deficit/hyperactivity disorder (ADHD). The authors hypothesized that nonaffected siblings of ADHD probands would have a response inhibition between that of ADHD probands and normal controls, although they resembled the controls at a behavioral level.
Method:
Participants were 25 ADHD probands with a family history of ADHD, their nonaffected siblings (n = 25), and 48 normal controls matched for age and IQ. All participants were between 6 and 17 years of age. The nonaffected siblings were compared with their ADHD siblings and with controls on measures reflecting different types of response inhibition.
Results:
The nonaffected siblings had results similar to those of the ADHD probands, who differed from the controls on all inhibition measures (p <.05).
Conclusions:
Siblings of ADHD probands, while not behaviorally expressing the disorder, have ADHD-associated deficits in response inhibition. This suggests that subtyping based on measures of response inhibition can help identify genetic susceptibility to ADHD. Children with a genetic vulnerability to ADHD may have hidden cognitive deficits in the absence of manifest behavioral symptoms. Therefore, they should be monitored to detect possible learning problems.