title: Is the inattentive subtype of ADHD different from the combined/hyperactive subtype?
abstract: OBJECTIVE
  To compare the ADHD combined/hyperactive subtype (ADHD/CH) to the ADHD inattentive subtype (ADHD/I) on the level of comorbidity, treatment response, and possible etiological factors.
  
  
  METHODS
  A total of 371 clinically referred children diagnosed with ADHD aged between 6 and 12 years are recruited for a double-blind, placebo-controlled trial of methylphenidate. Comorbidity, treatment response, and stress during pregnancy are assessed for each participant. Genotyping is done for the DAT, DRD4, and 5-HTT genes. Mothers report smoking or alcohol consumption during their pregnancy and their child's birth weight.
  
  
  RESULTS
  The ADHD/CH children show both a higher frequency of conduct disorder and good response to treatment, are exposed to more moderate stress during their mothers' pregnancy, and show a higher frequency of L/L genotype for the 5-HTT-linked polymorphic region.
  
  
  CONCLUSIONS
  The significant differences found between the ADHD/CH and the ADHD/I subtypes raise the possibility that the two may be separate disorders.
authors.affiliation: McGill University. grinat@douglas.mcgill.ca
authors.forename: Natalie
authors.initials: N
authors.lastname: Grizenko
authors.forename: Michael
authors.initials: M
authors.lastname: Paci
authors.forename: Ridha
authors.initials: R
authors.lastname: Joober
mesh_terms: D001289:Attention Deficit Disorder with Hyperactivity / Q000145:classification* / Q000175:diagnosis* / Q000235:genetics; D002648:Child; D003937:Diagnosis, Differential; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male