Is seeking treatment for depression predicted by a history of depression in relatives? Implications for family studies of affective disorder.

Most family studies of psychiatric illness ascertain probands through treatment facilities. If psychiatric illness in relatives influences the probability of treatment seeking, then the risk of illness in the relatives of treated probands will not be representative of the risk of illness in all probands. We have investigated this question in a population-based sample of female twins with a lifetime history of DSM-III-R defined major depression (MD) (N = 753), 36% of whom reported seeking professional help for their depression. Logistic and Cox regression methods were used. Treatment seeking for MD was significantly associated with age, education, comorbidity with anxiety disorders, degree of impairment and number of symptoms. Controlling for these predictors, treatment seeking was significantly predicted by the presence of one or more relatives with a lifetime diagnosis of MD (OR = 1.62). The probability of treatment seeking for MD in the proband was significantly increased if the affected relative: (i) had an onset of their MD prior that of the proband and; (ii) themselves sought treatment for their depression. Seeking treatment in this epidemiological sample of depressed women was associated with a 32% increase in risk of MD in relatives. Selecting probands for family studies from treated populations may select for families with an increased rate of illness. For MD, this artefact can explain only a modest proportion of the familial aggregation observed in prior family studies that utilized treated probands.