The research folks are gradually narrowing in on the cause of Parkinson’s — it relates to a bad-boy protein, alpha-synuclein, not properly folding and running amok with your dopamine. (“Proteins folding” always sounded like laundry to me.) But what causes the protein to mal-fold? Bad genes? Something in the environment?
On the environment side, pesticides are the favorite culprit. I’ve never bought this hypothesis for several reasons:
1) When Dr. James Parkinson wrote about “the shaking palsy” in 1817, there were no pesticides. Indeed, Parkinson’s has been recognized as a specific medical condition since ancient times by Ayurvedic physicians and the Greek physician Galen.
2) Hey, I’ve never been exposed to pesticides….or at least my exposure is minimal…so why do I have Parkinson’s?
3) I recall taking a look at pesticides early on and it seemed based on pretty weak science — just one study in the Central Valley of California, a place that’s got to be crawling with pesticides.
So, I contacted my research assistant (“pesticides Parkinson’s” in Google). What my research assistant found looked like a lot of research, but was almost entirely about two studies by UCLA in 2013 and 2014 — still valid, but obviously more research needs to be done on the pesticide angle. In the 2013 study the UCLA team discovered a link between Parkinson’s and the pesticide benomyl. Benomyl prevents the enzyme aldehyde dehydrogenase (ALDH) from converting aldehydes — organic compounds that are highly toxic to dopamine cells in the brain — into less toxic agents, thereby contributing to the risk of Parkinson’s. The 2014 study added 11 more equally delightful pesticides. The studies were careful to say things like “increase the risk of Parkinson’s ” or “two to six times more likely to develop Parkinson’s”. There is no single cause of Parkinson’s; instead, researchers would likely agree that Parkinson’s is caused by some complicated tangle of genetics and environmental factors…and the tangle is not the same from person to person.
The complicated tangle makes this article out of Taiwan so intriguing. The Taiwan study concludes that Parkinson disease (PD) appeared associated with 16 types of cancer. This is in contrast with earlier studies concluding PD patients had less risk of cancer (hey, one benefit). What’s different about this study? A major difference is genetics: previous studies have been of Western populations, while this study was of Asians. The study size was impressive: study group of 62,023 patients newly diagnosed with PD from 2004 through 2010 and 124,046 control participants without PD.
So what does the Taiwanese study have to do with pesticides? Nothing at this point, since the study did not include pesticide exposure . The authors note limitations in their research, including possible underestimation of PD incidence, smoking status not included in their analysis, speculation about pesticide exposure, and remaining questions regarding genetic correlations. The study concludes: “The striking differences between our study and the previous studies in Western cohorts suggest the importance of ethnicity and environmental exposures in disease pathogenesis.”
This study makes me wonder about the “environmental exposure” aspect: Would countries with large agricultural economies and weak pesticide management show higher incidences of cancer and/or PD? The Taiwanese study underscores the importance of doing (and sharing) PD research on populations across the globe. I’m looking forward to that global focus when I attend the World Parkinson’s Congress in September 2016.