Bay Area Doctors Find Parkinson's Disease Risk Much Greater in Some Exposed to Popular Herbicide

Genetic mutation leads to 11-fold increase in risk

Published Tuesday, October 9, 2012 12:01 am
by The Parkinson's Institute and Clinical Center

Sunnyvale, CA: Research conducted by The Parkinson’s Institute and Clinical Center (The PI) and the National Institute of Environmental Health Sciences (NIEHS) has found that exposure to one of the most widespread herbicides in the world may increase the risk of developing Parkinson’s disease, dramatically so in individuals carrying a common genetic variation. Lead author of the paper is The PI’s Associate Professor, Samuel Goldman, MD, MPH. The study was conducted by The PI’s Director of Clinical Research, Caroline Tanner, MD, PhD, and Freya Kamel, PhD, MPH of NIEHS, together with their colleagues. The findings will be published online in the journal Movement Disorders on October 9, 2012.

The study specifically looked at the risk of Parkinson’s disease in individuals exposed to 1,1′-dimethyl-4,4′-bipyridinium dichloride, an herbicide marketed under the name Paraquat. This herbicide has been widely used for decades in the farming of fruits and vegetables, to treat cotton before harvesting, and to kill weeds in fields before crop planting. In 2009, it was used on more than a million acres in California alone.

Research into the correlation between Paraquat exposure and the incidence of Parkinson’s disease was conducted among participants of the Agricultural Health Study (AHS), an ongoing project of the National Institutes of Health (NIH), the Environmental Protection Agency (EPA), and the National Institute of Occupational Safety and Health (NIOSH). Begun in 1993, the AHS includes 89,000 individuals residing in Iowa and North Carolina, many of whom worked as pesticide applicators (mostly farmers), and their spouses.

In the current study, 87 AHS participants were identified to have Parkinson’s disease; another 343 people without Parkinson’s disease were used as a control group. The researchers asked detailed questions about whether study participants used Paraquat in any job during their lifetime. In addition, their blood was tested to see if they had a common variant of the GSTT1 gene. When functioning properly, this gene makes an enzyme (glutathione-S-transferase T1) that protects the body from a variety of toxicants. However, approximately 20 percent of the general population has a defective version of the gene and completely lack this enzyme.

The study found that the risk of Parkinson’s disease was doubled in people who worked with Paraquat. Strikingly, among participants who had the defective GSTT1 gene variant, risk for developing Parkinson’s disease after working with Paraquat was increased 11-fold – one of the largest risks ever reported.

GSTT1 gene deletions are very common,” said Dr. Goldman. “Although our results require replication, carriers of this genetic variant potentially may be at extremely high risk of developing Parkinson’s disease from exposure to environmental toxicants such as Paraquat.”

Full citation: “Genetic Modification of the Association of Paraquat and Parkinson’s Disease”; Samuel M. Goldman, MD, MPH, Freya Kamel, PhD, MPH, G. Webster Ross, MD, Grace S. Bhudhikanok, PhD, Jane A. Hoppin, ScD, Monica Korell, MPH, Connie Marras, MD, PhD, Cheryl Meng, MS, David M. Umbach, PhD, Meike Kasten, MD, Anabel R. Chade, MD, Kathleen Comyns, MPH, Marie B. Richards, PhD, Dale P. Sandler, PhD, Aaron Blair, PhD, J. William Langston, MD, Caroline M. Tanner, MD, PhD. Movement Disorders; published online October 9, 2012 (DOI: 10.1002/mds.25216).

The Parkinson’s Institute and Clinical Center (The PI) is America’s only independent, non-profit organization providing comprehensive care to individuals with Parkinson’s disease (PD). The PI is a leader in researching causes and potential cures for PD. Since its founding in 1988, The PI has helped more than 50,000 PD patients better manage their disease, developed new treatments for this disease, and published ground-breaking research focused on closing the gap between science and practical care. To learn more about The Parkinson’s Institute, visit or call (408) 734-2800.

The National Institute of Environmental Health Sciences (NIEHS) supports research to understand the effects of the environment on human health and is part of the National Institutes of Health (NIH). For more information on environmental health topics, visit Subscribe to one or more of the NIEHS news lists ( to stay current on NIEHS news, press releases, grant opportunities, training, events, and publications.

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