Predictive Value of Family History on Severity of Illness

CONTEXT: If family history is associated with clinical features that are thought to index seriousness of disorder, this could inform clinicians predicting patients' prognosis and researchers selecting cases for genetic studies. Although tests of associations between family history and clinical features are numerous for depression, such tests are relatively lacking for other disorders. OBJECTIVE: To test the hypothesis that family history is associated with 4 clinical indexes of disorder (recurrence, impairment, service use, and age at onset) in relation to 4 psychiatric disorders (major depressive episode, anxiety disorder, alcohol dependence, and drug dependence). DESIGN: Prospective longitudinal cohort study. SETTING: New Zealand. PARTICIPANTS: A total of 981 members of the 1972 to 1973 Dunedin Study birth cohort (96% retention). MAIN OUTCOME MEASURES: For each disorder, family history scores were calculated as the proportion of affected family members from data on 3 generations of the participants' families. Data collected prospectively at the study's repeated assessments (ages 11-32 years) were used to assess recurrence, impairment, and age at onset; data collected by means of a life history calendar at age 32 years were used to assess service use. RESULTS: Family history was associated with the presence of all 4 disorder types. In addition, family history was associated with a more recurrent course for all 4 disorders (but not significantly for women with depression), worse impairment, and greater service use. Family history was not associated with younger age at onset for any disorder. CONCLUSIONS: Associations between family history of a disorder and clinical features of that disorder in probands showed consistent direction of effects across depression, anxiety disorder, alcohol dependence, and drug dependence. For these disorder types, family history is useful for determining patients' clinical prognosis and for selecting cases for genetic studies.