Understanding the Causes of Parkinson’s Disease

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A study published in NPJ Parkinson’s Disease (December 15, 2022 issue) rocked the medical community with shocking news about Parkinson’s Disease. According to the research, estimates for new cases of PD in the U.S. is 50% higher than what was previously thought.

The study, which gathered data on 6.7 million people ages 45 and over, plus 9.3 million people ages 65 and older, revealed 90,000 new PD cases diagnosed in the U.S. each year (compared with the previous estimate of 60,000 diagnoses).

Now, more than ever, it is critical to understand the nature and causes of this debilitating disease.

What Causes Parkinson’s Disease?

Parkinson’s disease manifests differently from one person to the next. The causes of the disease are equally complex, with a combination of genetic and environmental factors playing roles in its development. Common across people with PD loss is a depletion of dopaminergic neurons, which regulate movement, in the substantia nigra area of the brain.

Genetic Influences

Around 10 to 15% of all Parkinson’s stem from genetics, according to the Parkinson’s Foundation. Scientists have studied the DNA in people with Parkinson’s and found dozens of genetic mutations connected to the disease. Still not everyone with this mutation develops PD. Researchers are still trying to uncover why some people develop Parkinson’s, while others do not. It’s possible that just as some genes cause PD, other genes protect against it.

That being said, according to the Parkinson’s Foundation, around 90% of people with PD have no known genetic link. The organization further states that Parkinson’s results from a complex interaction between genes and environmental factors.

Environmental Factors

A broad array of environmental exposures influences PD development, including:

  • Traumatic brain injury
  • Occupation
  • Exposure to metals
  • Area of residence
  • Solvents and polychlorinated biphenyls (PCBs)

Although the Parkinson’s Foundation acknowledges each of the above factors as possible influencers in the development of Parkinson’s, the organization puts a greater emphasis on the role that pesticide and herbicide exposure plays in the disease’s formation.


Paraquat is a highly toxic herbicide. Its toxicity makes it effective at killing weeds. Scientists have linked this widely used commercial herbicide to Parkinson’s disease. Paraquat use has been banned in thirty-two countries according to The Michael J. Fox Foundation for Parkinson’s Research. The Unified Parkinson’s Advocacy Council joined with the Parkinson’s Foundation in drafting, signing, and sending letters to the U.S. Environmental Protection Agency urging it to cancel the registration of paraquat based on its connection with PD. Earthjustice filed a lawsuit on behalf of farmworker, public health, and environmental organizations, including The Michael J. Fox Foundation for Parkinson’s Research, challenging the EPA’s July 2021 decision approving continued paraquat use. The EPA is currently re-reviewing the registration of paraquat in the United States.

In September 2017, agricultural workers and farmers who were exposed to Paraquat and developed Parkinson’s disease filed a lawsuit. Defendants included Paraquat maker Syngenta and distributor Chevron.

According to plaintiffs’ complaints, their Parkinson’s disease resulted from multiple years of exposure to Paraquat. They also claim the defendants knew the chemicals cause harm to humans but sold the herbicide anyway for the purpose of killing weeds and failed to warn users of the product’s associated risk with developing Parkinson’s disease.

Although some plaintiffs alleged that the effects of Paraquat extended to residents in areas close to a place that was using the herbicide, most complaints stemmed from licensed applicators of the herbicide or people who worked in a place where Paraquat was applied.

In June 2021, a multidistrict litigation (MDL) for Paraquat was formed. This means all federal cases involving Paraquat were transferred to a single court—the Southern District of Illinois—to be heard before Judge Nancy J. Rosenstengel.

Levin Papantonio Rafferty is serving on the Plaintiffs’ Executive Committee for this MDL, in which more than 1,925 lawsuits are pending.