Beyond genetics: childhood affective trauma in bipolar disorder

Despite the demonstrated high heritability of bipolar disorder, few susceptibility genes have been identified and linkage and/or association studies have produced conflicting results. This search for susceptibility genes is hampered by several methodological limitations, and environmental risk factors for the disease (requiring incorporation into analyses) remain misunderstood. Among them, childhood trauma is probably the most promising environmental factor for further investigation. The objectives are to review the arguments in favor of an association between childhood trauma and bipolar disorder and to discuss the interpretations of such an observation. We computed a literature search using PubMed to identify relevant publications concerning childhood trauma and bipolar disorder. We also present some personal data in this field. Growing evidence suggests that incidences of childhood trauma are frequent and severe in bipolar disorder, probably affect the clinical expression of the disease in terms of suicidal behavior and age at onset, and also have an insidious influence on the affective functioning of patients between episodes. The relationships between childhood trauma and bipolar disorder suggest several interpretations, mainly a causal link, a neurodevelopmental consequence, or the intergenerational transmission of traumatic experiences. The neurobiological consequences of childhood trauma on a maturing brain remain unclear, although such stressors may alter the organization of brain development, leading to inadequate affective regulation. Childhood trauma is associated with bipolar disorder and its clinical expression and may interact with genetic susceptibility factors. Although not completely understood, the relationships between childhood trauma and bipolar disorder require further attention. Several suggestions for further exploration of this environmental factor and of its interaction with susceptibility genes are proposed.