title: Inhibition of motor responses in siblings concordant and discordant for attention deficit hyperactivity disorder.
abstract: 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.
authors.affiliation: Department of Psychiatry, The Hospital for Sick Children, University of Toronto, Toronto M5N 2L1, Canada. russell.schachar@sickkids.ca
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Schachar
authors.forename: Jennifer
authors.initials: J
authors.lastname: Crosbie
authors.forename: Cathy L
authors.initials: CL
authors.lastname: Barr
authors.forename: Tisha J
authors.initials: TJ
authors.lastname: Ornstein
authors.forename: James
authors.initials: J
authors.lastname: Kennedy
authors.forename: Molly
authors.initials: M
authors.lastname: Malone
authors.forename: Wendy
authors.initials: W
authors.lastname: Roberts
authors.forename: Abel
authors.initials: A
authors.lastname: Ickowicz
authors.forename: Rosemary
authors.initials: R
authors.lastname: Tannock
authors.forename: Shirley
authors.initials: S
authors.lastname: Chen
authors.forename: Tejaswee
authors.initials: T
authors.lastname: Pathare
mesh_terms: 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
chemical_list: D005819:Genetic Markers