Ethnicity and age at onset in bipolar spectrum disorders

IntroductionTo 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.

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.

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.DiscussionThe 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.

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.