title: Psychiatric comorbidity associated with DSM-IV ADHD in a nonreferred sample of twins.
abstract: OBJECTIVE
  To test the external validity of the dimensions and subtypes of DSM-IV attention-deficit/hyperactivity disorder (ADHD) by assessing the prevalence of psychiatric comorbidity.
  
  
  METHODS
  Eight- to 18-year-old twins with ADHD (n = 105) and without ADHD (n = 95) were recruited through local school districts. Comorbid disorders were assessed by structured diagnostic interviews with the parent and child and by a behavioral rating scale completed by the child's classroom teacher.
  
  
  RESULTS
  Symptoms of inattention were associated with lower intelligence and higher levels of depression, whereas symptoms of hyperactivity-impulsivity were associated more strongly with symptoms of oppositional defiant disorder (ODD) and conduct disorder (CD). All DSM-IV subtypes were associated with higher rates of ODD and CD in comparison with controls, and the combined type was associated with more disruptive behavior disorder symptoms than the other 2 subtypes. The combined type and predominantly inattentive type were associated with more symptoms of depression than controls or the predominantly hyperactive-impulsive type.
  
  
  CONCLUSIONS
  These results provide support for the discriminant validity of the dimensions and subtypes of DSM-IV ADHD and suggest that clinicians should carefully screen for comorbid disorders as part of a comprehensive assessment of ADHD.
authors.affiliation: University of Colorado, Boulder Institute for Behavioral Genetics 80309, USA. willcutt@Colorado.edu
authors.forename: E G
authors.initials: EG
authors.lastname: Willcutt
authors.forename: B F
authors.initials: BF
authors.lastname: Pennington
authors.forename: N A
authors.initials: NA
authors.lastname: Chhabildas
authors.forename: M C
authors.initials: MC
authors.lastname: Friedman
authors.forename: J
authors.initials: J
authors.lastname: Alexander
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology; D019958:Attention Deficit and Disruptive Behavior Disorders / Q000209:etiology / Q000235:genetics / Q000523:psychology; D002648:Child; D015897:Comorbidity; D019955:Conduct Disorder / Q000209:etiology / Q000235:genetics / Q000523:psychology; D003866:Depressive Disorder / Q000209:etiology / Q000235:genetics / Q000523:psychology; D005260:Female; D006801:Humans; D008297:Male; D011569:Psychiatric Status Rating Scales / Q000592:standards*; D015203:Reproducibility of Results; D012307:Risk Factors; D012680:Sensitivity and Specificity