The clinical characteristics of major depression as indices of the familial risk to illness

BACKGROUND: From both a clinical and an aetiological perspective, major depression (MD) is probably a heterogeneous condition. We attempt to relate these two domains. METHOD: We examined which of an extensive series of clinical characteristics in 646 female twins from a population-based register with a lifetime diagnosis of MD predicts the risk for MD in co-twins. MD was defined by DSM-III-R criteria. RESULTS: Four variables uniquely predicted an increased risk for MD in the co-twin: number of episodes, degree of impairment and co-morbidity with panic disorder or bulimia. One variable uniquely predicted decreased risk: co-morbidity with phobia. Variables that did not uniquely predict risk of MD in the co-twin included age at onset, number and kind of depressive symptoms, treatment seeking, duration of the longest episode and co-morbidity with generalised anxiety disorder and alcohol dependence. CONCLUSIONS: Our results suggest that the clinical features of MD can be meaningfully related to the familial vulnerability to illness, particularly with respect to recurrence, impairment and patterns of co-morbidity. (July 1994)