Inhibition of motor responses in siblings concordant and discordant for attention deficit hyperactivity disorder.
OBJECTIVE
The authors sought to determine whether nonaffected siblings of ADHD probands have a motor response inhibition deficit and to assess concordance for this inhibition deficit in ADHD-concordant and ADHD-discordant sibling pairs.


METHODS
ADHD-concordant pairs (21 probands and their affected siblings), ADHD-discordant pairs (18 probands and their nonaffected siblings), and a group of unrelated, demographically balanced, healthy individuals (N=24) were compared on measures of response inhibition, ADHD behavior, impairment, and environmental risk.


RESULTS
Concordant-pair probands, their affected siblings, and discordant-pair probands exhibited inhibitory control impairment relative to healthy comparison subjects. The performance of nonaffected siblings was intermediate between that of ADHD children and the healthy comparison subjects. Group differences persisted after age was controlled, and performance was not correlated with the number of ADHD symptoms. In ADHD-concordant sibling pairs, there was a significant relationship between proband and sibling inhibition deficit. In ADHD-discordant sibling pairs, inhibition deficit was evident in half of the nonaffected siblings of probands with an inhibition deficit. Groups did not differ in exposure to environmental risks.


CONCLUSIONS
Impaired inhibitory control aggregates in the family members of individuals with ADHD and may serve as an indicator of genetic vulnerability to the disorder.
Schachar
Russell J
RJ
Department of Psychiatry, The Hospital for Sick Children, University of Toronto, Toronto M5N 2L1, Canada. russell.schachar@sickkids.ca
Crosbie
Jennifer
J
Barr
Cathy L
CL
Ornstein
Tisha J
TJ
Kennedy
James
J
Malone
Molly
M
Roberts
Wendy
W
Ickowicz
Abel
A
Tannock
Rosemary
R
Chen
Shirley
S
Pathare
Tejaswee
T
D001289:Attention Deficit Disorder with Hyperactivity / Q000235:genetics*; D005819:Genetic Markers; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D007266:Inhibition, Psychological; D010641:Phenotype; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D012307:Risk Factors; D035781:Siblings / Q000523:psychology
D005819:Genetic Markers