Parkinson's Disease: Associations with Environmental Exposures

Parkinson's disease is a group of motor system disorders including tremor of the extremities, rigidity of the limbs and body, slowness of movement (bradykinesia), and impaired balance and coordination (postural instability). These motor deficits are due to the progressive degeneration of brain cells called dopaminergic neurons within the basal ganglia and substantia nigra. As more dopaminergic neurons are lost, the symptoms of Parkinson’s disease worsen over time, and may lead to further effects on health such as difficulty speaking, sleep disorders, and depression. Although a low percentage of Parkinson’s disease cases can be attributed to genetic factors, the causes of many cases remain unknown. A growing number of studies have reported that certain environmental exposures may be associated with Parkinson's disease or mechanisms suspected or known to lead to Parkinson's disease.

NTP is conducting two scoping reviews on this topic. One ongoing project is a scoping review to systematically map the evidence of the associations between exposures to environmental chemicals considered broadly and Parkinson's disease. Early in the process, the environmental chemical paraquat dichloride was identified as a chemical of interest for further review. Paraquat is an herbicide that is used to control weeds in a variety of agricultural and non-agricultural settings. NTP developed a scoping review and evidence maps of published scientific literature. A considerable body of evidence was identified on paraquat exposure and Parkinson’s disease that can be used in developing future systematic reviews. Researchers can explore the health effects data related to Parkinson’s disease that was collected using evidence maps - interactive, sortable visualizations that can be used to identify data rich and data poor areas of research.