Defining a developmental subtype of bipolar disorder in a sample of nonreferred adults by age at onset

Objective: To test the hypothesis that the age at onset of bipolar disorder would identify a developmental subtype of bipolar disorder in adults characterized by increased levels of irritability, chronic course, rapid cycling, and comorbidity with attention deficit hyperactivity disorder. Methods: Forty-four adult subjects diagnosed with bipolar disorder were selected from large family studies of youth with and without attention deficit hyperactivity disorder. These subjects were stratified by the age at onset in childhood (younger than 13 years; n = 8, 18%), adolescence (13-18 years; n = 12, 27%, or adulthood (older than 19 years; n = 24, 55%). All subjects were administered structure diagnostic interviews and a brief cognitive battery. Results: In contrast with adult-onset bipolar disorder, child-onset bipolar disorder was associated with a longer duration of illness, more irritability than euphoria, a mixed presentation, a more chronic or rapid-cycling course, and increased comorbidity with childhood disruptive behavior disorders and anxiety disorders. Conclusion: Stratification by age at onset of bipolar disorder identified subgroups of adult subjects with differing clinical correlates. This pattern of correlates is consistent with findings documented in children with pediatric bipolar disorder and supports the hypothesis that child-onset bipolar disorder may represent a developmental subtype of the disorder.