Depression and anxiety commonly co-occur and have been associated with cognitive biases and executive function deficits across development. Twin studies indicate considerable genetic overlap between internalizing symptoms and cognitive processes. However, relatively little is known about how genetic, environmental and cognitive processes contribute to the co-occurrence of depression and anxiety symptoms over time. Twin modelling analyses were conducted using three longitudinal population-based twin samples – ECHO, G1219 and TEDS. The first half of this thesis focused on developmental associations between depression and four different anxiety symptom clusters. First, the phenotypic and genetic structure of symptoms was examined cross-sectionally in childhood, adolescence and young adulthood. Developmental differences in the aetiology of the relationship between depression and anxiety were found, with genetic influences becoming less disorder-specific from adolescence. Next, longitudinal analyses found that both stable and newly emerging genes, and to a lesser extent non-shared environmental effects, contributed to the co-occurrence of depression and anxiety across adolescence and young adulthood. The second half of this thesis focused on cognitive processes involved in the aetiology and maintenance of depression and anxiety. First, associations between anxiety sensitivity dimensions and depression and anxiety symptoms were investigated. Results identified disorder-specific versus shared cognitive content in depression and anxiety that was generally unchanged across development and was underpinned by broad genetic vulnerability. Second, association between mindfulness, anxiety sensitivity and depression was investigated. Mindfulness was found to be moderately heritable and the relationship between attentional control aspect of mindfulness, depression and anxiety sensitivity was largely due to shared genetic liability. Finally, using an experimental study conducted in sixty-one 8-10 years old children, depression and anxiety were found to be independently associated with poorer attentional control. This attentional deficit may account for some of the attentional biases often observed in anxious and depressed children on tasks investigating processing of emotional stimuli.
|Date of Award||2016|
|Supervisor||Helena Zavos (Supervisor) & Thalia Eley (Supervisor)|