The cyclothymic temperament in healthy controls and familially at risk individuals for mood disorder: endophenotype for genetic studies?

Background: The modern concept of affective disorders focuses increasingly on the study of subthreshold conditions on the border of manic or depressive episodes. Indeed, a spectrum of affective conditions spanning from temperament to clinical episodes has been proposed by the senior author. As bipolar disorder is a familial illness, an examination of cyclothymic temperament (CT) in controls and relatives of bipolar patients is of major relevance. Methods: We recruited a total sample of 177 healthy symptom-free volunteers. These controls were divided into three groups. The first one is comprised of 100 normal subjects with a negative familial affective history (NFH); the second of 37 individuals, with positive affective family history (PFH); and a third of 40 subjects, with at least one sib or first-degree kin with bipolar disorder type I according to the DSM-IV (BPR). The last two groups defined at risk individuals. We interviewed all subjects with CT, as described by the senior author. Results: We found a statistically significant difference in the rates of CT between the subjects in BPR versus others. CT was also more prevalent in the PFH compared with NFH. Additionally, the simple numeration of the CT traits exhibited gradation in the distribution of individuals inside the NFH, PFH and BPR. Finally, categorically defined CT and CT traits predominated in females. Limitation and conclusion: Although not all relatives of bipolar probands were studied, our results exhibit an aggregation of CT in families with affective disorder-and more specifically those with bipolar background. These results allow us to propose the importance of including CT for phenotypic characterization of bipolar disorder. Furthermore, our results support a spectrum concept of bipolar disorder, whereby CT is distributed in ascending order in the well-relatives of those with depressive and bipolar disorders. We submit that this temperament represents a behavioral endophenotype, serving as a link between molecular and behavioral genetics.