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Parkinson's disease risk greater in those exposed to trichloroethylene

Symptoms of disease may appear 10 to 40 years following exposure

A novel study in twins found that exposure to trichloroethylene (TCE) -- a hazardous organic contaminant found in soil, groundwater, and air -- is significantly associated with increased risk of Parkinson's disease (PD).

Possibility of developing this neurodegenerative disease is also linked to perchloroethylene (PERC) and carbon tetrachloride (CCI4) exposure according to the study appearing today in Annals of Neurology, a journal published by Wiley-Blackwell on behalf of the American Neurological Association and Child Neurology Society.

The National Institute of Neurological Disorders and Stroke (NINDS) estimates that as many as 500,000 Americans have PD and more than 50,000 new cases are diagnosed annually. While there is much debate regarding cause of PD, studies suggest that genetic and environmental factors likely trigger the disease which is characterized by symptoms such as limb tremors, slowed movement, muscle stiffness, and speech impairment. Several studies have reported that exposure to solvents may increase risk of PD, but research assessing specific agents is limited.

The current epidemiological study, led by Drs. Samuel Goldman and Caroline Tanner with The Parkinson's Institute in Sunnyvale, California, investigated exposure to TCE, PERC and CCI4 and risk of developing PD. The team interviewed 99 twin pairs from the National Academy of Sciences/National Research Council World War II Veteran Twins Cohort in which one twin had PD and one didn't, inquiring about lifetime occupations and hobbies. Lifetime exposures to six specific solvents previously linked to PD in medical literature -- n-hexane, xylene, toluene, CCl4, TCE and PERC -- were inferred for each job or hobby.

The findings are the first to report a significant association between TCE exposure and PD -- a more than 6-fold increased risk. Researchers also found that exposure to PERC and CCI4 tended toward significant risk of developing the disease. "Our study confirms that common environmental contaminants may increase the risk of developing PD, which has considerable public health implications," commented Dr. Goldman.

TCE, PERC and CCI4 have been used extensively worldwide, with TCE noted as a common agent in dry-cleaning solutions, adhesives, paints, and carpet cleaners. Despite the Food and Drug Administration (FDA) banning the use of TCE as a general anesthetic, skin disinfectant, and coffee decaffeinating agent in 1977, it is still widely used today as a degreasing agent. In the U.S., millions of pounds of TCE are still released into the environment each year and it is the most common organic contaminant found in ground water, detected in up to 30% of drinking water supplies in the country.

While this study focused on occupational exposures, the solvents investigated are pervasive in the environment. The authors suggest that replication of well-characterized exposures in other populations is necessary. Dr. Goldman concluded, "Our findings, as well as prior case reports, suggest a lag time of up to 40 years between TCE exposure and onset of PD, providing a critical window of opportunity to potentially slow the disease process before clinical symptoms appear."

In a release issued on September 28, 2011 the Environmental Protection Agency (EPA) announced that TCE is carcinogenic to humans.

This study is published in Annals of Neurology. Media wishing to receive a PDF of this article may contact

Full citation: "Solvent Exposures and Parkinson's Disease Risk in Twins"; Samuel M Goldman, Patricia J Quinlan, G Webster Ross, Connie Marras, Cheryl Meng, Grace S Bhudhikanok, Kathleen Comyns, Monica Korell, Anabel R Chade, Meike Kasten, Benjamin Priestley, Kelvin L Chou, Hubert H Fernandez, Franca Cambi, J William Langston and Caroline M Tanner. Annals of Neurology; Published Online: November 14, 2011 (DOI:10.1002/ana.22629).

Author Contact: To arrange an interview with Dr. Sam Goldman or Dr. Caroline Tanner, please contact Hallie Baron at, 415-928-2317 (office) or 415-793-7435 (cell).

About the Authors: Sam Goldman, MD, MPH, is an Associate Professor and Caroline M. Tanner, MD, PhD, is Director of Clinical Research with The Parkinson's Institute and Clinical Center (PI), America's only independent, non-profit organization, providing comprehensive care to individuals with Parkinson's disease (PD). PI is a leader in researching causes and potential cures for PD. Since its founding in 1988, it 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, go to or call 408-734-2800.

About the Journal

Annals of Neurology, the official journal of the American Neurological Association and the Child Neurology Society, publishes articles of broad interest with potential for high impact in understanding the mechanisms and treatment of diseases of the human nervous system. All areas of clinical and basic neuroscience, including new technologies, cellular and molecular neurobiology, population sciences, and studies of behavior, addiction, and psychiatric diseases are of interest to the journal.

About Wiley-Blackwell

Wiley-Blackwell is the international scientific, technical, medical, and scholarly publishing business of John Wiley & Sons, with strengths in every major academic and professional field and partnerships with many of the world's leading societies. Wiley-Blackwell publishes nearly 1,500 peer-reviewed journals and 1,500+ new books annually in print and online, as well as databases, major reference works and laboratory protocols. For more information, please visit or our new online platform, Wiley Online Library (, one of the world's most extensive multidisciplinary collections of online resources, covering life, health, social and physical sciences, and humanities.

Dawn Peters | EurekAlert!
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