Depressed preschoolers with bipolar family history: a group at high risk for later switching to mania?

Earlier age of onset of an episode of depression and family history of bipolar disorder (FHBPD) are well known to be associated with increased rates of switching to mania in childhood major depressive disorder (MDD). These findings suggest that the youngest samples of depressed children who have FHBPD might be at very high risk for switching. The finding of a valid depressive syndrome in preschool children has raised the question of whether mania could also manifest at this early stage. We investigated FHBPD among three preschool study groups: a depressed group and two nondepressed comparison groups (attention deficit hyperactivity disorder/oppositional defiant disorder, no disorder). Increased FHBPD was found among the depressed group. Based on this, we explored whether the depressed subgroup with FHBPD (MDD + FHBPD) had a unique constellation of depressive symptoms compared to the depressed subgroup without FHBPD (MDD with no FHBPD). The MDD + FHBPD group was found to have an increased frequency of the MDD symptom of "restlessness and moves around a lot" as compared with the MDD with no FHBPD group. The question of whether this symptom could be an early precursor of later mania was explored. These findings taken together suggest that early risk factors for switching to mania may be present in a subgroup of depressed preschoolers. Longitudinal follow-up of depressed preschool samples to determine rates of switching to mania later in development is critical to determine whether such findings represent early risk factors. Future studies that directly investigate age-appropriate mania manifestations in preschool samples are now warranted.