title: Using admixture analysis to examine birth-cohort effects on age at onset of bipolar disorder.
abstract: OBJECTIVE
  It is suggested that age at onset (AAO) of bipolar I disorder (BP-I) is decreasing. We tested for a birth-cohort effect on AAO using admixture analysis.
  
  
  METHODS
  A clinical sample of 3896 BP-I cases was analysed using two approaches: (i) in a subsample with untruncated AAO × birth year distribution (n = 1865), we compared the best-fitting model for the observed AAO in patients born ≤1960 and >1960, (ii) to control for potential confounders, two separate subsamples born ≤1960 and >1960 were matched for age at interview (n = 250), and a further admixture analysis was undertaken.
  
  
  RESULTS
  The two approaches indicated that the proportion of cases in the early AAO category was significantly greater in cases born >1960; manic onsets were also more frequent in the early onset BP-I cases born >1960.
  
  
  CONCLUSIONS
  The decrease in AAO of BP-I in recent birth-cohorts appears to be associated with an increase in the proportion of cases in the early onset subgroup; not with a decrease in the mean AAO in each putative subgroup. This could indicate temporal changes in exposure to risk factors for mania.
authors.affiliation: Department de Biostatistiques, ER4/EA3974, Université Paris 6 et APHP, UF de biostatistique, GH Pitié-Salpêtrière, Paris, France.
authors.forename: J-L
authors.initials: JL
authors.lastname: Golmard
authors.affiliation: Academic Psychiatry, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK.|Centre for Affective Disorders, Institute of Psychiatry, London, UK.
authors.forename: J
authors.initials: J
authors.lastname: Scott
authors.affiliation: INSERM, Unité 955, IMRB, Equipe de Psychiatrie Génétique, Créteil, France.|Foundation Fondamental, Hôpital A. Chenevier, Créteil, France.|AP-HP, Groupe Henri Mondor-Albert Chenevier, Pôle de Psychiatrie, Créteil, France.|Faculté de Médecine, IFR10, Université Paris Est Creteil, Créteil, France.
authors.forename: B
authors.initials: B
authors.lastname: Etain
authors.affiliation: Department of Psychiatry, Lausanne University Hospital, Prilly, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Preisig
authors.affiliation: Department of Psychiatry, HUG, Hôpital Belle-Idée, Geneva, Switzerland.
authors.forename: J-M
authors.initials: JM
authors.lastname: Aubry
authors.affiliation: INSERM, Unité 955, IMRB, Equipe de Psychiatrie Génétique, Créteil, France.|Foundation Fondamental, Hôpital A. Chenevier, Créteil, France.|AP-HP, Groupe Henri Mondor-Albert Chenevier, Pôle de Psychiatrie, Créteil, France.|Faculté de Médecine, IFR10, Université Paris Est Creteil, Créteil, France.
authors.forename: C
authors.initials: C
authors.lastname: Henry
authors.affiliation: INSERM, Unité 955, IMRB, Equipe de Psychiatrie Génétique, Créteil, France.|Foundation Fondamental, Hôpital A. Chenevier, Créteil, France.|Faculté de Médecine, IFR10, Université Paris Est Creteil, Créteil, France.
authors.forename: S
authors.initials: S
authors.lastname: Jamain
authors.affiliation: AP-HM, Hôpital Sainte Marguerite, Pôle de psychiatrie, Pavillon SOLARIS, Marseille, France.
authors.forename: J-M
authors.initials: JM
authors.lastname: Azorin
authors.affiliation: INSERM, Unité 955, IMRB, Equipe de Psychiatrie Génétique, Créteil, France.|Foundation Fondamental, Hôpital A. Chenevier, Créteil, France.|AP-HP, Groupe Henri Mondor-Albert Chenevier, Pôle de Psychiatrie, Créteil, France.|Faculté de Médecine, IFR10, Université Paris Est Creteil, Créteil, France.
authors.forename: M
authors.initials: M
authors.lastname: Leboyer
authors.affiliation: Foundation Fondamental, Hôpital A. Chenevier, Créteil, France.|Sorbonne Paris Cité, Université Paris Diderot, UMR-S 1144, Paris, France.|AP-HP, Groupe Saint-Louis-Lariboisière-F. Widal, Paris, France.|Inserm, U1144, Paris, France.
authors.forename: F
authors.initials: F
authors.lastname: Bellivier
mesh_terms: D000328:Adult; D017668:Age of Onset; D001714:Bipolar Disorder / Q000175:diagnosis / Q000453:epidemiology*; D015988:Cohort Effect; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012307:Risk Factors
keywords: age at onset; bipolar I disorder; birth-cohort effect