Genetic aetiology of mood disorders

Advances towards the understanding of the etiological mechanisms involved in mood disorders provide interesting yet diverse hypotheses and promising models. In this context, molecular genetics has now been widely incorporated into genetic epidemiological research in psychiatry. Affective disorders and, in particular, bipolar affective disorder (BPAD) have been examined in many molecular genetic studies which have covered a large part of the genome, specific hypotheses such as mutations have also been studied. Most recent studies indicate that several chromosomal regions may be involved in the aetiology of BPAD. Other studies have reported the presence of anticipation in BPAD and in unipolar affective disorder (UPAD). In parallel to these new developments in molecular genetics, the classical genetic epidemiology, represented by twin, adoption and family studies, provided additional evidence in favour of the genetic hypothesis in mood disorders. Moreover, these methods have been improved through models to test the gene-environment interactions. In addition to genetic approaches, psychiatric research has focused on the role of psychosocial factors in the emergence of mood disorders. In this approach, psychosocial factors refer to the patient's social life context as well as to personality dimensions. Abnormalities in the social behavior such as impairment in social relationships have been observed during episode of affective disorders, and implicated in the etiology of affective disorders. Further, gender and socio-economic status also emerged as having a possible impact on the development of affective disorders. Finally, the onset and outcome of affective disorders could also be explained by interactions between the social life context and the individual's temperament and personality. The importance of temperament and personality characteristics in the etiology of depression has been emphasized in various theories, although disagreement exists with regard to terminology and the etiology. While significant advances have been done in these two major fields of research, it appears that integrative models, taking into account the interactions between biological (genetic) factors and social (psychosocial environment) variables offer the most reliable way to approach the complex mechanisms involved in the etiology and outcome of mood disorders. This chapter will review some of the most promising genetic and psychosocial hypotheses in mood disorders that can be integrated in interactive models.