Twin-study shows occupational chemical worker risk of Parkinson’s?

Well, not really.

From an NIH media release:

A new research report contributes to the increasing evidence that repeated occupational exposure to certain chemical solvents raises the risk for Parkinson’s disease. Researchers analyzed the occupational histories of twins in which one of the pair developed the neurodegenerative disorder, and assessed that twin’s likelihood of exposure to six chemicals previously linked to Parkinson’s. Of the six chemicals investigated, researchers concluded that two common chemical solvents, trichloroethylene (TCE) and perchloroethylene (PERC), are significantly linked to development of this disease. This study, supported in part by the National Institute of Neurological Disorders and Stroke (NINDS), a part of the National Institutes of Health, appears in the Nov. 14, 2011 issue of Annals of Neurology…

Below is the study abstract.

Despite the claim it is readily apparent that underlying statistical results are goofy — insignificant and lousy quality data (note wide confidence intervals/error bars).

This report does not contribute to anything other than the trashcan.


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

One thought on “Twin-study shows occupational chemical worker risk of Parkinson’s?”

  1. This is inane. It STARTS WITH THE ASSUMPTION that the twin with PD has the disease because of exposure to one of the subject chemicals. Then proceeds to try to guess which is most likely, based on which one(s) they are most likely to have been exposed to, based on guesses which are based on general info about their lifetime activities.
    And, -“the potential public health implications are substantial”-!?
    These guys have PhD’s, do they?

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