Date of Graduation


Document Type


Degree Type



Eberly College of Arts and Sciences



Committee Chair

Amy Fiske


Depression commonly co-occurs with Parkinson's disease (PD). Psychosocial stressors and biochemical changes associated with PD have both been implicated in the etiology of depression in PD. The purpose of the current study was to examine whether genetic or environmental influences contribute to the increased risk for depressive symptoms among individuals with PD in a population of twins. Among individuals with PD, 24% endorsed a moderate-severe level of depressive symptoms, and 64% endorsed at least a mild level of depressive symptoms. Case-control results indicated that PD is a significant risk factor for both mild (OR = 3.11, CI = 1.82-5.31) and moderate-severe (OR = 3.23, CI = 1.77-5.89) depressive symptoms, adjusting for age, sex, and prior history of major depression. Odds ratios were not significantly attenuated in the co-twin control analysis compared to the case control analysis for either mild or moderate-severe depressive symptoms, suggesting that genetic influences are unlikely to account for the increased risk of depressive symptoms among PD patients. Further support for environmental rather than genetic influences on the PD-depression relation was revealed by examining the risk of depressive symptoms among co-twins of PD patients versus co-twins of non-PD controls. Controlling for age, sex, and prior history of depression, PD in the co-twin was not a risk factor for mild or moderate-severe depressive symptoms in twins without PD. These findings indicate that environmental influences likely play an important role in the etiology of depressive symptoms in individuals with Parkinson's disease. Alternatively, brain changes associated with PD may heighten biological vulnerability to depressive symptoms.