This interdisciplinary project is aimed at studying genetic and environmental factors influencing individual differences of adolescent depressiveness. The classical twin method is used to estimate the contributions of genetic and environmental factors in depressiveness. The depressiveness is understood as an individual's tendency to experience depressive moods and states in various life situations. The questionnaire to assess the depressiveness is Children’s Depression Inventory by M.Covacs, and the stressful life events questionnaire, which is aimed at tapping the most frequently appearing stressful events in adolescent’s life. The main sample consisted of 196 pairs of Russian-speaking twins aged 13-17 (M-15,2), 72 pairs of monozygotic twins, 81 pair of same-sex dizygotic twins, and 43 pairs of different-sex dizygotic twins. Structural equation methods (OpenMX Software) were used to estimate the contributions of genetic and environmental factors to individual differences of adolescent depressiveness.
The best fitting model for the CDI composite score was AE (additive genetics and nonshared environment) with a strong contribution of genetic component (А= 0,57; E=0, 43). The same model fitted well to the Negative Mood (А= 0,61; E=0, 39) and Externalization (А= 0,38; E=0,62). As for the Negative Self-Esteem scale, it was the full ACE model that fitted best, where almost half of the variance was explained by the nonshared environmental factors, and the common and nonshared environmental factors explain the rest (А= 0,25; С=0,2; E=0,55). For the Angedony and Withdrawal scale it was the environmental CE model that fitted best (С= 0,33;E=0,67).
The perceived stressful life events and their relative quantity was best explained by the full ACE model (А=0,3; C=0,21; E=0,49). The contribution of genetic component to the variance of quantity of stressful life events reveals a possibility of genotype-environment correlation, that means - a person with a “depressive” genotype appears to receive the corresponding environmental influence. To examine a hypothesis on genotype-environment correlation as applies to stressful life events, we computed the correlations of stressful life events level in the first twin pair member with a depressiveness level of the second pair member for different kinds of twins. Since the results appear to be statistically significant (the MZ correlation is slightly higher than DZ), we cannot dismiss the hypothesis of genotype-environmental correlation.
In overall, our study allowed to estimate the relative contributions of genetic and environmental factors to individual differences in adolescent depressiveness, as well as its link with individual differences in stressful life events. The perspectives for the future investigation are to study the concrete environmental factors and individual genes influencing the development of adolescent depressiveness.
