Mania symptoms in a Swedish longitudinal population study: The roles of childhood trauma and neurodevelopmental disorders

•Childhood traumatic experiences (CTEs) and Neurodevelopmental disorders (NDDs) have separately been associated with increased risk for juvenile mania.•We found that these risk effects are additive: Adolescents with both exposures had more mania symptoms than adolescents with only one exposure.•CTEs and NDDs often occur together.•Patients presenting with one risk factor should be examined for the other risk factor.•These patients should be monitored for potentially increased risk of juvenile mania. Adult psychiatric disorders are associated with both childhood traumatic experiences (CTEs) and neurodevelopmental disorders (NDDs). CTEs and NDDs frequently co-occur in childhood, but their combined risk effect on the emergence of juvenile mania symptoms has not yet been examined. In a population-representative Swedish twin study, CTEs and NDDs were assessed in 3,348 nine-year old twins born between 1998 and 2001, and treated as dichotomous predictors (any CTEs, any NDDs). Follow-up data were gathered at age 15 through parental reports of mania symptoms, yielding a symptom count score. Both CTEs and NDDs at age 9 contributed uniquely to an increase in mania symptoms at age 15. Children with both risk factors had 1.6 times the rate of mania symptoms as children with CTEs-only (Incidence rate ratio [IRR] 1.63, 95% CI 1.37-1.93), and 1.3 times the rate of mania symptoms as children with NDDs-only (IRR 1.26, 95% CI 1.06-1.50). There was no evidence for an interactive effect of CTEs and NDDs. NDDs showed a trend towards having a larger effect on mania symptoms than CTEs (NDDs-only vs. CTEs-only: IRR 1.29, 95% CI 0.99-1.68). Although it is a strength of the study that the data on exposures and outcome were collected prospectively, parental recall of CTEs was required and CTEs may be under-reported. NDDs are at least as important as CTEs in the development of mania symptoms, and their risk is additive. Those with a history of both CTEs and NDDs should be monitored closely for the development of more severe psychiatric presentations.