title: Examining the comorbidity between attention deficit hyperactivity disorder and bipolar I disorder: a meta-analysis of family genetic studies.
abstract: OBJECTIVE
  The existence of comorbidity between attention deficit hyperactivity disorder (ADHD) and bipolar I disorder has been documented in clinical and epidemiological studies, in studies of children and adults, and in diagnosed ADHD and bipolar I patient samples. Yet questions remain about the validity of diagnosing bipolar I disorder in ADHD youth. The authors aim to clarify these issues by reviewing family genetic studies of ADHD and bipolar I disorder.
  
  
  METHODS
  The authors applied random-effects meta-analysis to family genetic studies of ADHD and bipolar I disorder. Twenty bipolar proband studies provided 37 estimates of the prevalence of ADHD in 4,301 relatives of bipolar probands and 1,937 relatives of comparison probands. Seven ADHD proband studies provided 12 estimates of the prevalence of bipolar I disorder in 1,877 relatives of ADHD probands and 1,601 relatives of comparison probands.
  
  
  RESULTS
  These studies found a significantly higher prevalence of ADHD among relatives of bipolar probands and a significantly higher prevalence of bipolar I disorder among relatives of ADHD probands. These results could not be accounted for by publication biases, unusual results from any one observation, sample characteristics, or study design features. The authors found no evidence of heterogeneity in the ADHD or bipolar family studies.
  
  
  CONCLUSIONS
  The results suggest that ADHD plus bipolar comorbidity cannot be accounted for by misdiagnoses, but additional research is needed to rule out artifactual sources of comorbidity. More research is also needed to determine whether comorbidity of ADHD and bipolar I disorder constitutes a familial subtype distinct from its constituent disorders, which if confirmed would have implications for diagnostic nosology and genetic studies.
authors.affiliation: Departments of Psychiatry and Neuroscience and Physiology, SUNY Upstate Medical University, NY, USA. sfaraone@childpsychresearch.org
authors.forename: Stephen V
authors.initials: SV
authors.lastname: Faraone
authors.forename: Joseph
authors.initials: J
authors.lastname: Biederman
authors.forename: Janet
authors.initials: J
authors.lastname: Wozniak
mesh_terms: D000293:Adolescent; D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology* / Q000235:genetics; D001714:Bipolar Disorder / Q000453:epidemiology* / Q000235:genetics; D002648:Child; D015897:Comorbidity; D005190:Family / Q000523:psychology; D006801:Humans; D015995:Prevalence; D012306:Risk