title: Age at onset in bipolar I disorder: two may be better than three subgroups.
abstract: OBJECTIVE
  Age at onset in bipolar disorder is related to prognosis and to treatment response. However, it is not clear if there are three or two subgroups in relation to age at onset. The objective of this study is to analyze the number of subgroups in relation to age at the beginning of the disease in a representative sample of bipolar I patients and to compare the subgroups in relation to clinical variables.
  
  
  METHODS
  We included 169 patients diagnosed with bipolar I disorder. Normal mixture analysis was performed. The subgroups of patients formed above were compared regarding clinical characteristics. Patients were followed-up during six years.
  
  
  RESULTS
  We found three ages at onset subgroups. The early onset group (18.2±2 years) included 34% of the patients. The second group (26.1±5.5 years) included 44% of the patients. The third group (50.9±9.1 years) included 22% of the patients. Early and intermediate onset groups were not significantly different, and had more family history of affective disorders, more psychotic symptoms, more history of suicide attempts and more history of drug abuse history than the late onset group.
  
  
  CONCLUSIONS
  Our results suggest that there are three groups of age at onset but early and intermediate groups are similar in relation to clinical variables. The late onset group includes almost a quartile of patients and has different clinical profile.
authors.affiliation: Departamento de Psiquiatría. Hospital Santiago Apóstol, Sistema Vasco de Salud Mental, Vitoria, España. Electronic address: anamaria.gonzalez-pintoarrillaga@osakidetza.net.
authors.forename: Ana
authors.initials: A
authors.lastname: González Pinto
authors.forename: Sara
authors.initials: S
authors.lastname: Barbeito
authors.forename: Francisco
authors.initials: F
authors.lastname: José Díaz
authors.forename: Patricia
authors.initials: P
authors.lastname: Vega
authors.forename: Fernando
authors.initials: F
authors.lastname: Mosquera
authors.forename: Purificación
authors.initials: P
authors.lastname: López
authors.forename: Susana
authors.initials: S
authors.lastname: Alberich
authors.forename: Sonia
authors.initials: S
authors.lastname: Ruiz de Azua
authors.forename: Amaia
authors.initials: A
authors.lastname: Ugarte
authors.forename: Manuel
authors.initials: M
authors.lastname: Martín
authors.forename: José
authors.initials: J
authors.lastname: de León