PORTLAND, OR —Higher serum levels of polychlorinated biphenyls (PCBs) are associated with increased risk of Parkinson’s disease in two independent study populations, according to research presented at the Fourth World Parkinson Congress.
Samuel Goldman, MD, MPH
PCBs are persistent environmental pollutants that are detectable in most people despite a worldwide ban on their production that has been in place for more than 20 years. PCBs cause selective dopaminergic toxicity in animal models, but have been minimally studied in Parkinson’s disease, the researchers said.
The investigators recently reported a significantly increased risk of Parkinson’s disease associated with higher levels of serum PCBs in a case–control study of Alaska Native people. In the present study, they investigated this association in a demographically dissimilar study population.
They identified people with Parkinson’s disease within the Agricultural Health Study, a cohort of pesticide applicators and their spouses in Iowa and North Carolina. They also randomly selected controls matched for age, sex, and state. They confirmed Parkinson’s disease diagnoses by in-person neurologist evaluation and consensus review. PCB congeners 118, 138, 153, and 180 were measured as ng/g lipid in serum using gas chromatography-mass spectroscopy. To assess dose-response, the researchers constructed quartiles for each congener and for the sum of congeners. The used logistic regression, adjusting for age, gender, and state, to calculate odds ratios.
Ninety-seven people with Parkinson’s disease and 113 controls were included in the study. About 25% of the participants were women. Mean age was 69. Parkinson’s disease was associated with higher levels of PCBs. A significant dose-response was seen across quartiles. Participants in the second, third, and fourth quartiles of total PCB levels had a 1.7-, 2.4-, and 2.7-fold greater risk of Parkinson’s disease, respectively, compared with participants in the lowest quartile of total PCB levels. Odds ratios were similar in the Agricultural Heath Study and the Alaska study. In both studies, PCB levels correlated positively with age but not with disease duration, which argues against reverse causation, the researchers said.
—Jake Remaly