This study aims to investigate whether: familial history of affective disorder, subclinical depressive symptoms and life events (LEs) are predictive of a later development of mood disorder (onset). In a high-risk study, 234 healthy monozygotic and dizygotic twins with and without a co-twin history of affective disorder (high and low risk twins, respectively) were identified through nationwide registers and assessed from 2002 to 2005. Participants were followed longitudinally at 6-months intervals for up to nine years and finally reassessed with a personal interview to obtain information on whether they had an onset. During the follow-up period (mean time 7.0 years), 36 participants (15.4%) developed onset. Onset was significantly associated with risk status (Hazard ratio (HR) = 1.38, 95% CI 1.08-1.76), female sex, HR = 2.70, 95% CI 1.19-6.97, age HR = 0.97, 95% CI 0.93-0.99), and also with baseline Hamilton 17 score (HR = 1.30, 95% CI 1.13-1.48), Becks Depression Inventory 21 (HR = 1.14, 95% CI, 1.05-1.24) and neuroticism (HR = 1.08, 95% 1.02-1.12). Finally, the experience of LEs lifetime before baseline predicted onset (HR = 1.20, 95% CI 1.01-1.46) and the experience of LEs during follow-up also predicted onset (HR = 1.06, 95% CI 1.01-1.11). These findings suggest that young individuals at familial risk of affective disorders are at enhanced risk of onset and at further risk when having female sex and more subclinical depressive symptoms at baseline. Further, they seem to experience more LEs and to be more vulnerable to these.
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