Clinical indices of familial depression in the Swedish Twin Registry

Objective: Although familial factors certainly contribute to the etiology of major depression (MD), further information is needed about which clinical features of depressive illness index the familial vulnerability in MD. Method: Lifetime MD and associated clinical features were assessed at personal interview in 27 230 individual twins, including 4080 onsets of MD, from the Swedish National Twin Registry. Analyses were conducted using Cox proportional hazards models. Results: Three clinical variables in a depressed twin predicted the hazard ratio for MD in the cotwin. In the order of the strength of the association, these were: number of endorsed A criteria, age at onset, and number of episodes. Conclusion: Certain clinical features of MD are significant, albeit modest, indices of the familial vulnerability to MD. Individuals with a high familial/genetic risk for MD tend to have an early age at onset, meet most of the symptomatic DSM criteria and suffer recurrences.