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Background: Difficult temperament in infancy is a risk factor for forms of later internalizing and externalizing psychopathology, including depression and anxiety. A better understanding of the roots of difficult temperament requires assessment of its early development with a genetically informative design. The goal of this study was to estimate genetic and environmental contributions to individual differences in infant negative emotionality, their persistence over time and their influences on stability between 5 and 18 months of age. Method: Participants were 244 monozygotic and 394 dizygotic twin pairs (49.7% male) recruited from birth. Mothers rated their twins for negative emotionality at 5 and 18 months. Longitudinal analysis of stability and innovation between the two time points was performed in Mplus. Results: There were substantial and similar heritability (approximately 31%) and shared environmental (57.3%) contributions to negative emotionality at both 5 and 18 months. The trait’s interindividual stability across time was both genetically- and environmentally- mediated. Evidence of innovative effects (i.e., variance at 18 months independent from variance at 5 months) indicated that negative emotionality is developmentally dynamic and affected by persistent and new genetic and environmental factors at 18 months. Conclusions: In the first two years of life, ongoing genetic and environmental influences support temperamental negative emotionality but new genetic and environmental factors also indicate dynamic change of those factors across time. A better understanding of the source and timing of factors on temperament in early development, and role of sex, could improve efforts to prevent related psychopathology. [ABSTRACT FROM AUTHOR]

Background and Objectives: Depression has been associated with alterations in social functioning. Decoding and understanding others' mental states and adaptive reasoning are important for social functioning. This study examined theory of mind (ToM) and socio-moral reasoning (SMR) in adolescent girls with and without depression. Within the depression group, we examined associations between relevant clinical features (depression severity, anxiety symptoms and borderline personality traits) and ToM and SMR.Methods: A cross-sectional study was conducted, whereby 43 adolescent girls (mean age = 16.19, SD = 1.24) meeting full or subthreshold criteria for depression and 40 adolescent girls (mean age = 15.44, SD = 1.24) with no psychiatric diagnosis were recruited. ToM was assessed using the Movie for the Assessment of Social Cognition; SMR was evaluated via the Socio-Moral Reasoning Aptitude Level task.Results: Analyses of covariance indicated that adolescents with depression did not differ from controls in ToM abilities but showed lower socio-maturity scores on the SMR task. This difference disappeared after controlling for the number of words used to justify responses. Amongst adolescents with depression, multiple linear regression analyses revealed that higher levels of borderline personality traits were associated with lower levels of mentalization (ToM task), and more severe depressive symptoms were associated with lower socio-moral maturity stages (SMR task) LIMITATIONS: Directional associations were not studied, and the sample included only girls.Conclusions: Findings may help to explain clinical heterogeneity in social cognitive functioning observed in individuals with depression. [ABSTRACT FROM AUTHOR]