Solvent exposures and Parkinson disease risk in twins.
Level 4 - case-series / case-control
Discordant twin-pair case-control study
PubMed 22083847 · doi:10.1002/ana.22629
What was done
Ninety-nine twin pairs discordant for Parkinson disease (PD) from the National Academy of Sciences/National Research Council World War II Veteran Twins Cohort were interviewed regarding lifetime occupations and hobbies using job task-specific questionnaires. Exposures to six specific solvents selected a priori were estimated by expert raters blinded to case status.
What was found
Ever exposure to trichloroethylene (TCE) was significantly associated with increased risk of PD (OR 6.1; 95% CI 1.2–33; p = 0.034). Exposure to perchloroethylene (PERC) showed a non-significant trend toward increased risk (OR 10.5; 95% CI 0.97–113; p = 0.053), as did carbon tetrachloride (OR 2.3; 95% CI 0.9–6.1; p = 0.088). Results were similar for estimates of exposure duration and cumulative lifetime exposure.
Why it matters
The discordant twin design helps control for genetic background and early-life confounders, strengthening epidemiologic evidence linking specific solvent exposures—particularly ubiquitous chemicals like TCE—to Parkinson disease risk.
Limits
The sample size is relatively small (99 discordant pairs), leading to imprecise effect estimates and wide confidence intervals. Exposure assessment relied on retrospective self-report of job histories rather than direct exposure measurements, and the sample was restricted to male World War II veterans.
Cited by
- supports Exposure to trichloroethylene (TCE) and perchloroethylene (PCE) is associated in a twin study with a 500% increased risk of Parkinson's disease.