Parsing the heterogeneity : an examination of genetic and environmental influences on intermediate phenotypes of Major Depressive Disorder

Major Depressive Disorder (MDD) is a prevalent and debilitating disorder associated with a tremendous societal burden (Greenberg & Birnbaum, 2005). Despite significant research efforts, the etiology of MDD remains elusive, in part because studies have examined MDD as a single homogeneous syndrome, which could limit our understanding of the disorder’s genetic and environmental architecture. Individuals with MDD have substantial phenotypic heterogeneity, and different symptom presentations are likely to have diverse etiological precedents. Focusing on intermediate phenotypes of MDD, which are closer to the underlying genetic and environmental causes, might help to mitigate these concerns. This dissertation combines three studies focused on understanding how genetic and environmental factors, as well as their interaction, contribute to the development of relevant intermediate phenotypes. Specifically, these three studies use innovative methods to measure genetic and/or environmental contributions to attentional bias, reward processing, and depression symptom dimensions. This line of research will help establish individual difference factors that predict intermediate phenotypes of MDD and contribute to advancing our understanding of the etiology of depression.Psycholog