Ethnicity and Age at Onset in Bipolar Spectrum Disorders

Introduction: To determine the influence of ethnicity on the age at onset (AAO) and further understand the significance of AAO as a clinical marker of bipolar and schizoaffective disorders. Methods: Admixture analysis was used to identify sub-groups characterized by differences in AAO. Differences in clinical features were analyzed for these sub-groups using multivariate logistic regression. Comparisons were made with previous studies using the 2-Sample Kolmogorov-Smirnov Test. Results: Admixture analysis yielded a combination of 2 normal theoretical distributions with means (SD) of 16.9 (3.6) for the early-onset sub-group and 24.4 (9.2) years for the late-onset sub-group. The sub-groups were divided by a cut-off of 22 years. There were significant differences between the early and late onset bipolar patient populations regarding substance abuse comorbidity (P=.044) and psychotic features (P=.015). Ethnicity did not have a significant influence on the AAO. Discussion: The associations between early-onset and higher incidence of psychosis and substance abuse in our sample are consistent with other studies exploring the AAO in bipolar disorder. Conclusion: Our findings support the notion of AAO as a clinical marker for the underlying heterogeneity of bipolar spectrum disorders. In particular, we found a strong overlap of early AAO with clinical features associated with greater severity and poor outcome.