Genetic risk of depression and stress-induced negative affect in daily life.

BACKGROUND A bias to develop negative affect in response to daily life stressors may be an important depression endophenotype, but remains difficult to assess. AIMS To assess this mood bias endophenotype, uncontaminated by current mood, in the course of daily life. METHOD The experience sampling method was used to collect multiple appraisals of daily life event-related stress and negative affect in 279 female twin pairs. Cross-twin, cross-trait associations between dailylife mood bias and DSM-IV depression were conducted. RESULTS Probands whose co-twins were diagnosed with lifetime depression showed a stronger mood bias to stress than those with co-twins without such a diagnosis, independent of probands' current depressive symptoms and to a greater extent in monozygotic twins than in dizygotic twins. CONCLUSIONS Genetic liability to depression is in part expressed as the tendency to display negative affect in response to minor stressors in daily life. This trait may represent a true depression endophenotype.