title: Age at onset in patients with bipolar I and II disorder: a comparison of large sample studies.
abstract: Bipolar Disorder (BD) is a leading cause of disability worldwide and factors contributing to its burden include chronic relapsing course, comorbidity, suicide risk, and early age at onset (AAO). In particular, recent investigation has shown that BD onset may occur earlier than previously believed, even though whether BDI and II are different in such regard is still debated. Reduced samples may, moreover, limit the confidence in the published studies, with geographic issues, in turn, representing potentially conditioning factors. The present review was aimed to select and analyze large sample studies comparing AAO in BDI vs II patients.
  
  
  
  A PubMed literature search was performed, considering English-written articles published up to December 2015, comparing AAO in BDI vs II patients with sample size≥100 subjects per group.
  
  
  
  Seventeen studies were considered suitable for revision, with 8 studies reporting statistically significant differences and 9 not. Among studies reporting statistically significant differences, mostly conducted in Europe, 6 showed an earlier AAO in BDI, while 2 in BDII subjects.
  
  
  
  Only studies with large samples included, considering AAO as a continuous variable, and providing a comparison between the bipolar subtypes.
  
  
  
  Our findings suggest that AAO per se does not seem to reliably differentiate BDI from BDII patients and that such variable should likely be investigated in the context of other clinical characteristics, in order to assess its overall influence over BD course. Geographic factors may, in turn, play a potential role with future investigation warranted to further explore this specific issue.
authors.affiliation: Department of Psychiatry, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy; Department of Psychiatry, Bipolar Disorders Clinic, Stanford Medical School, Stanford University, CA, USA. Electronic address: bernardo.dellosso@unimi.it.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Dell'Osso
authors.affiliation: Department of Psychiatry, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Grancini
authors.affiliation: Department of Psychiatry, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Vismara
authors.affiliation: Department of Psychiatry, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: De Cagna
authors.affiliation: Department of Psychiatry, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Maggi
authors.affiliation: Department of Psychiatry, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Mattia
authors.initials: M
authors.lastname: Molle
authors.affiliation: Department of Psychiatry, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Cremaschi
authors.affiliation: Department of Psychiatry, Bipolar Disorders Clinic, Stanford Medical School, Stanford University, CA, USA.
authors.forename: Shefali
authors.initials: S
authors.lastname: Miller
authors.affiliation: Department of Psychiatry, Bipolar Disorders Clinic, Stanford Medical School, Stanford University, CA, USA.
authors.forename: Terence A
authors.initials: TA
authors.lastname: Ketter
authors.affiliation: Department of Psychiatry, University of Milan, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: A Carlo
authors.initials: AC
authors.lastname: Altamura
mesh_terms: D017668:Age of Onset; D001714:Bipolar Disorder / Q000453:epidemiology*; D015897:Comorbidity; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male
keywords: Age at onset (AAO); Bipolar Disorder type I (BDI); Bipolar Disorder type II (BDII)