Objectives: To compare the incidence and prevalence of bipolar disorder (BD) between adolescence and young adulthood; to explore the stability and consequences of adolescent BD in young adulthood; to determine the rate of switching from major depressive disorder (MDD) to BD; and to evaluate the significance of subsyndromal BD (SUB).
Methods: A large, randomly selected community sample (n=1507) received diagnostic assessments twice during adolescence, and a stratified subset (n=893) was assessed again at 24years of age. In addition, direct interviews were conducted with all available first-degree relatives. Five mutually exclusive groups, based on diagnoses in adolescence, were compared: BD (n=17), SUB (n=48), MDD (n=275), disruptive behavior disorder (n=49), and no-disorder (ND) controls (n=307).
Results: Lifetime prevalence of BD was approximately 1% during adolescence and 2% during young adulthood. Lifetime prevalence for SUB was approximately 5%. Less than 1% of adolescents with MDD ‘switched’ to BD by age 24. Adolescents with BD had an elevated incidence of BD from 19 to 23 years, while adolescents with SUB exhibited elevated rates of MDD and anxiety disorders in young adulthood. BD and SUB groups both had elevated rates of antisocial symptoms and borderline personality symptoms. Compared to the ND group, adolescents with BD and SUB both showed significant impairment in psychosocial functioning and had higher mental-health treatment utilization at age 24 years of age. The relatives of adolescents with BD and SUB had elevated rates of MDD and anxiety disorders. The relatives of SUB probands had elevated BD, while the relatives of BD had elevated rates of SUB and borderline symptoms.
Conclusions: Adolescent BD showed significant continuity across developmental periods and was associated with adverse outcomes during young adulthood. Adolescent SUB was also associated with adverse outcomes in young adulthood, but was not associated with an increased incidence of BD. Due to high rates of comorbidity with other disorders, definitive conclusions regarding the specific clinical significance of SUB must await studies with larger numbers of ‘pure’ SUB cases.