Negative life events as an account of age-related differences in the genetic aetiology of depression in childhood and adolescence

Background: Many twin studies have reported that the genetic aetiology of depression differs according to age, with genetic influences being more important for adolescents than younger children. We sought to examine whether this age-related increase in the relative importance of genetic factors is due to an increase in gene-environment correlation specifically involving negative life events. Method: Questionnaires were sent to the families of a population-based sample of twins aged between 8 and 17 years. Parents of all the twins and adolescents aged 11 and over were asked to complete the Mood and Feelings Questionnaire (Costello & Angold, 1988) and a modified version of the Life Events Checklist (Johnson & McCutcheon, 1980). Responses were obtained from 1468 families and data were analysed using genetic model fitting. Bivariate analysis of 1) negative life events and 2) behaviour-dependent life events and depression symptoms was undertaken separately for children (aged 8 to 10 years) and adolescents (aged 11 to 17 years). Differences in genetic and environmental parameters across age groups were tested. Results: Adolescence was associated with a greater number of behaviour-dependent life events. Genetic covariation of negative life events and depression was greater for adolescents than for children. Conclusions: Bivariate model fitting was consistent with the greater heritability of depression seen in adolescence being due to an increase in gene-environment correlation involving negative life events. However, the effects of genes associated specifically with maturation in adolescence, the possibility of 'person' effects and the role of other environmental factors also need to be considered