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Age at onset in Sardinian bipolar I patients: evidence for three subgroups.

Manchia M, Lampus S, Chillotti C, Sardu C, Ardau R, Severino G, Del Zompo M

Section of Clinical Pharmacology, Department of Neuroscience BB Brodie, Clinical Psychopharmacology Center, University of Cagliari, Cagliari, Italy.

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.

Published 11 April 2008 in Bipolar Disord, 10(3): 443-6.
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