title: Risk of bipolar disorder and schizophrenia in relatives of people with attention-deficit hyperactivity disorder.
abstract: BACKGROUND
  Attention-deficit hyperactivity disorder (ADHD) is associated with bipolar disorder and schizophrenia, and it has been suggested that combined bipolar disorder and ADHD is aetiologically distinct from the pure disorders.
  
  
  OBJECTIVE
  To clarify whether ADHD shares genetic and environmental factors with bipolar disorder and schizophrenia.
  
  
  METHODS
  By linking longitudinal Swedish national registers, we identified 61 187 persons with ADHD (the proband group) and their first- and second-degree relatives, and matched them with a control group of people without ADHD and their corresponding relatives. Conditional logistic regression was used to determine the risks of bipolar disorder and schizophrenia in the relatives of the two groups.
  
  
  RESULTS
  First-degree relatives of the ADHD proband group were at increased risk of both bipolar disorder (odds ratio (OR) = 1.84-2.54 for parents, offspring and full siblings) and schizophrenia (OR = 1.71-2.22 for parents, offspring and full siblings). The risks of bipolar disorder and schizophrenia among second-degree relatives were substantially lower than among full siblings.
  
  
  CONCLUSIONS
  These findings suggest that the co-occurrence of ADHD and bipolar disorder as well as ADHD and schizophrenia is due to shared genetic factors, rather than representing completely aetiologically distinct subsyndromes.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden. Henrik.Larsson@ki.se
authors.forename: Henrik
authors.initials: H
authors.lastname: Larsson
authors.forename: Eleonore
authors.initials: E
authors.lastname: Rydén
authors.forename: Marcus
authors.initials: M
authors.lastname: Boman
authors.forename: Niklas
authors.initials: N
authors.lastname: Långström
authors.forename: Paul
authors.initials: P
authors.lastname: Lichtenstein
authors.forename: Mikael
authors.initials: M
authors.lastname: Landén
mesh_terms: D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology / Q000235:genetics*; D001714:Bipolar Disorder / Q000453:epidemiology / Q000235:genetics*; D015897:Comorbidity; D005190:Family; D005260:Female; D059647:Gene-Environment Interaction; D020022:Genetic Predisposition to Disease; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D016017:Odds Ratio; D012306:Risk; D012559:Schizophrenia / Q000453:epidemiology / Q000235:genetics*; D013548:Sweden / Q000453:epidemiology