14 November 2011 Last updated at 04:57 GMT Share this pageEmailPrint
Study links Parkinson's disease to industrial solvent
By Neil Bowdler
Health reporter, BBC News
An international study has linked an industrial solvent to Parkinson's disease.
Researchers found a six-fold increase in the risk of developing Parkinson's in individuals exposed in the workplace to trichloroethylene (TCE).
Although many uses for TCE have been banned around the world, the chemical is still used as a degreasing agent.
The research was based on analysis of 99 pairs of twins selected from US data records.
Parkinson's can result in limb tremors, slowed movement and speech impairment, but the exact cause of the disease is still unknown, and there is no cure.
Research to date suggests a mix of genetic and environmental factors may be responsible. A link has previously been made with pesticide use.
The researchers from institutes in the US, Canada, Germany and Argentina, wanted to examine the impact of solvent exposure - specifically six solvents including TCE.
They looked at 99 sets of twins, one twin with Parkinson's, the other without.
Because twins are genetically very similar or identical and often share certain lifestyle characteristics, twins were thought to provide a better control group, reducing the likelihood of spurious results.
The twins were interviewed to build up a work history and calculate likely exposure to solvents. They were also asked about hobbies.
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Further larger-scale studies are needed to confirm the link”
Dr Michelle Gardner
The findings are presented as the first study to report a "significant association" between TCE exposure and Parkinson's and suggest exposure to the solvent was likely to result in a six-fold increase in the chances of developing the disease.
The study also adjudged exposure to two other solvents, perchloroethylene (PERC) and carbon tetrachloride (CCl4), "tended towards significant risk of developing the disease".
No statistical link was found with the other three solvents examined in the study - toluene, xylene and n-hexane.
"Our study confirms that common environmental contaminants may increase the risk of developing Parkinson's, which has considerable public health implications," said Dr Samuel Goldman of The Parkinson's Institute in Sunnyvale, California, who co-led the study published in the journal Annals of Neurology.
He added: "Our findings, as well as prior case reports, suggest a lag time of up to 40 years between TCE exposure and onset of Parkinson's, providing a critical window of opportunity to potentially slow the disease before clinical symptoms appear."
TCE has been used in paints, glue, carpet cleaners, dry-cleaning solutions and as a degreaser. It has been banned in the food and pharmaceutical industries in most regions of the world since the 1970s, due to concerns over its toxicity.
In 1997, the US authorities banned its use as an anaesthetic, skin disinfectant, grain fumigant and coffee decaffeinating agent, but it is still used as a degreasing agent for metal parts.
A computer image of affected neurons in the brain of Parkinson's patients
Groundwater contamination by TCE is widespread, with studies estimating up to 30% of US drinking water supplies are contaminated with TCE. In Europe, it was reclassified in 2001 as a "category 2" carcinogen, although it is still used in industrial applications.
PERC, like TCE, is used as a dry-cleaning agent and degreasing agent, and is found in many household products. CCl4's major historical use was in the manufacture of chlorofluorocarbons for use as refrigerants, but it has also been used a fumigant to kill insects in grain.
Commenting on the paper, Dr Michelle Gardner, Research Development Manager at Parkinson's UK, said: "This is the first study to show that the solvent TCE may be associated with an increased risk of developing Parkinson's.
"It is important to highlight that many of the previous uses of this solvent have been discontinued for safety reasons over 30 years ago and that safety and protection in work places where strong chemicals such as this solvent are used has greatly improved in recent years."
She also called for more research to confirm the link between TCE and other solvents with Parkinson's.
"Further larger-scale studies on populations with more defined exposures are needed to confirm the link," she said.
Solvent exposures and parkinson disease risk in twins
Samuel M. Goldman MD, MPH1,*, Patricia J. Quinlan MPH, CIH2, G. Webster Ross MD3, Connie Marras MD, PhD4, Cheryl Meng MS1, Grace S. Bhudhikanok PhD1, Kathleen Comyns MPH1, Monica Korell MPH1, Anabel R. Chade MD5, Meike Kasten MD6, Benjamin Priestley MPH1, Kelvin L. Chou MD7, Hubert H. Fernandez MD8, Franca Cambi MD, PhD9, J. William Langston MD1, Caroline M. Tanner MD, PhD1
Article first published online: 14 NOV 2011
Several case reports have linked solvent exposure to Parkinson disease (PD), but few studies have assessed associations with specific agents using an analytic epidemiologic design. We tested the hypothesis that exposure to specific solvents is associated with PD risk using a discordant twin pair design.
Ninety-nine twin pairs discordant for PD ascertained from the National Academy of Sciences/National Research Council World War II Veteran Twins Cohort were interviewed regarding lifetime occupations and hobbies using detailed job task?specific questionnaires. Exposures to 6 specific solvents selected a priori were estimated by expert raters unaware of case status.
Ever exposure to trichloroethylene (TCE) was associated with significantly increased risk of PD (odds ratio [OR], 6.1; 95% confidence interval [CI] 1.2?33; p = 0.034), and exposure to perchloroethylene (PERC) and carbon tetrachloride (CCl4) tended toward significance (respectively: OR, 10.5; 95% CI, 0.97?113; p = 0.053; OR, 2.3; 95% CI, 0.9?6.1; p = 0.088). Results were similar for estimates of exposure duration and cumulative lifetime exposure.
Exposure to specific solvents may increase risk of PD. TCE is the most common organic contaminant in groundwater, and PERC and CCl4 are also ubiquitous in the environment. Our findings require replication in other populations with well-characterized exposures, but the potential public health implications are substantial. ANN NEUROL 2011
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