title: Age at onset in Sardinian bipolar I patients: evidence for three subgroups.
abstract: OBJECTIVE
  We studied age at onset (AAO) in order to assess the presence of different subgroups in a homogeneous genetic population, such as the Sardinian population.
  
  
  METHODS
  Admixture analysis was applied in order to identify a model of separate normal distribution of AAO characterized by different means, variances and population proportions to allow for evaluation of different subgroups in a sample of 181 unrelated patients of Sardinian origin with bipolar disorder (BP) type I. The Mann-Whitney test was used to compare the means of AAO between subjects with a history of suicide attempts and subjects with no such history.
  
  
  RESULTS
  The best-fitting model had three components with means (SD) of 18.1 (2.3), 24.3 (5.3) and 41 (11.5) years, comprising 36%, 39% and 25% of the sample, respectively. We obtained two cut-off points at 21 and 33 years, enabling the sample to be divided into three subgroups. The Mann-Whitney test revealed a difference between the mean AAO of subjects with a positive history of suicide attempts and that of subjects with no such history (p = 0.041).
  
  
  CONCLUSIONS
  We found three AAO sub-groups in our sample of BP I patients of Sardinian origin. Our findings add further support to the hypothesis whereby AAO acts as a clinical marker of biological heterogeneity in BP.
authors.affiliation: Section of Clinical Pharmacology, Department of Neuroscience BB Brodie, Clinical Psychopharmacology Center, University of Cagliari, Cagliari, Italy.
authors.forename: Mirko
authors.initials: M
authors.lastname: Manchia
authors.forename: Simona
authors.initials: S
authors.lastname: Lampus
authors.forename: Caterina
authors.initials: C
authors.lastname: Chillotti
authors.forename: Claudia
authors.initials: C
authors.lastname: Sardu
authors.forename: Raffaella
authors.initials: R
authors.lastname: Ardau
authors.forename: Giovanni
authors.initials: G
authors.lastname: Severino
authors.forename: Maria
authors.initials: M
authors.lastname: Del Zompo
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D017668:Age of Onset; D001714:Bipolar Disorder / Q000453:epidemiology* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011569:Psychiatric Status Rating Scales; D012044:Regression Analysis; D018709:Statistics, Nonparametric; D013405:Suicide / Q000523:psychology / Q000706:statistics & numerical data