Eenzaamheid in de Vroege Adolescentie: Ouderlijke Context, DNA Methylatie en Tussenliggende Mechanismen

Loneliness is commonly described as the distressing feeling that arises when there is a discrepancy between the social relationships a person desires and those they perceive themselves to have, either in terms of quantity or quality. Given that loneliness in early adolescence has been linked to a range of adverse outcomes, a thorough examination of factors associated with adolescent loneliness is essential. This dissertation seeks to advance our understanding of loneliness in early adolescence by examining factors at multiple levels of analysis. Specifically, it examines social environmental factors (i.e., parent-adolescent relationship quality and parenting behaviors), epigenetic mechanisms (i.e., DNA methylation), and potential intermediary processes or endophenotypes (i.e., stress physiology and attentional biases in information processing), as well as how these levels interact. In Part I of this dissertation, we applied a multi-informant approach to investigate potential bidirectional longitudinal associations between aspects of parent-adolescent relationship quality, namely, parental warmth and hostility, and loneliness in early adolescence. We focused both on the shared level of relationship quality as perceived by both mothers and adolescents, and on the mother-adolescent discrepancies in these reports. The findings indicated that higher levels of perceived parental hostility in the parent-adolescent relationship were associated with more loneliness over time. In addition, loneliness predicted larger mother-adolescent discrepancies in reports of parental hostility over time. Results further suggested both shared and distinct patterns in how depressive symptoms and loneliness related to perceived parental warmth and hostility over time in early adolescence. In Part II of this dissertation, we investigated the potential role of epigenetic mechanisms, particularly DNA methylation, in the association between perceived parenting behaviors and loneliness in early adolescence. Specifically, we examined whether DNA methylation acted as either a mediator or a moderator of this association. Rather than supporting a mediating role of DNA methylation, our findings suggest that DNA methylation of the glucocorticoid receptor gene (NR3C1) moderates the association between adverse parenting behaviors and loneliness. Specifically, higher levels of NR3C1 methylation increased adolescents' vulnerability to the negative effects of parental psychological control. These findings highlight the relevance of considering epigenome-environment interactions in loneliness research and suggest that moderation models may offer a more informative framework than mediation models in this area. In Part III of this dissertation, we aimed to understand how DNA methylation in stress-related genes might be associated with loneliness in early adolescence by examining two potential intermediary processes or endophenotypes, namely stress reactivity and attentional biases in social information processing. Although higher NR3C1 methylation was associated with attenuated physiological stress responses and a blunted skin conductance response was associated with more loneliness, no significant indirect effects linking NR3C1 methylation to loneliness via stress reactivity emerged. Furthermore, our findings provided no evidence of significant associations between DNA methylation in stress-related genes, attentional biases in social information processing, and loneliness. Taken together, these results do not support physiological stress reactivity or attentional biases as endophenotypic pathways connecting DNA methylation to loneliness in early adolescence. In summary, this dissertation examined factors at multiple levels of analysis to deepen our understanding of loneliness during early adolescence. Beyond addressing important gaps in the literature, the findings also raise new questions. By offering directions for future research, we hope this work will inspire future studies to build on our insights and further advance the field of loneliness research.