Clinical features of major depressive disorder in adolescents and their relatives: impact on familial aggregation, implications for phenotype definition, and specificity of transmission.

Three questions were addressed using family study data from a community sample: (a) Which clinical features of major depressive disorder (MDD) in adolescents are associated with elevated rates of MDD in relatives? (b) Which features of MDD in relatives distinguish family members of depressed adolescents from relatives of adolescents without mood disorders (NMD)? and (c) Do depressed adolescents with particular features have higher proportions of depressed relatives with the same features? Participants included 268 MDD adolescents, 401 NMD adolescents, and their 2,202 first-degree relatives. Rates of MDD were highest among relatives of depressed adolescents with recurrent episodes and greater impairment. Depression severity best distinguished the relatives of depressed adolescents from relatives of controls. Specific clinical features did not aggregate in families.