Temperament has been defined as a heritable personality factor that remains stable over time and establishes a person’s baseline level of reactivity, mood, and energy (7). While normal variations in temperament exist within the population, it has been suggested that a dysregulation of temperament is the fundamental abnormality that predisposes to the development of bipolar spectrum disorders, with more extreme variations in temperament conferring greater risk (4,8–10). In this model, affective temperament is influenced by numerous genes of small effect, resulting in a continuous distribution of mood regulation and reactivity. More extreme manifestations of affective temperament may in turn predispose individuals to episodes of mania and depression. Such a model is consistent with the observation of milder forms of the bipolar phenotype in family members of probands with BD and with a polygenic mode of transmission. By focusing on the underlying affective dysregulation, temperament may be a phenotype that is more sensitive and closer to the underlying biological abnormalities.
