Genetic and Environmental Contributions to Trajectories of Depressive Symptoms

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Depression is a complex mental health disorder, predicted to be the highest global burden of disease by 2030. Research has examined the antecedents of adolescent depression in order to limit and prevent depression from occurring. However, depression during this phase of development is multifactorial and variability in depression is characterised by important features such as the age of onset, chronicity and severity. Identifying these features, and how depressive mood changes across time along with potential risk factors may aid in our understanding of the nature of adolescent depression and help develop new interventions and treatments.

This thesis uses longitudinal methods to explore the nature of trajectories of depressive symptoms and examine how genetic, and early environmental risk factors contribute to trajectories of depressive symptoms across adolescence and young adulthood in a UK population based cohort, the Avon Longitudinal Study of Parents and Children. Using group-based and multilevel frameworks, trajectories of depressive symptoms are estimated across adolescence and then various risk factors are explored to investigate how these trajectories change across time.

Genetic risk for depression, childhood bullying, female sex and childhood trauma are all associated with less favourable trajectories of depressive symptoms. Importantly, several risk factors are associated with changes in depression across time, and not just at certain stages of development. This implies they have lasting effects and that it may be possible to identify when particular risk factors are having their greatest effect on later depression.

This work provides further evidence that depressive symptoms across adolescence to young adulthood are complex and associated with both genetic and environmental contributions. Examining depressive symptoms across time within a longitudinal framework provides a powerful opportunity to examine the nature of depression in more detail than in previous research.
Date of Award23 Jan 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorDavid J Manley (Supervisor), Nicholas John Timpson (Supervisor) & George B Leckie (Supervisor)

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