December 7, 2005 - Growing Link Between Parkinson's and Chemical Exposure

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Evidence continues to build strengthening the suspicion of scientists that long-term exposure to toxic compounds, particularly pesticides, can destroy neurons and trigger Parkinson's in some people. So far, several pesticides have been show to cause Parkinson's symptoms in animals. But hundreds of agricultural and industrial chemicals probably play a role, they believe.

Researchers don't use the word "cause" when linking environmental exposures to a disease. Instead, epidemiologists look for clusters and patterns in people, and neurobiologists test theories in animals. If their findings are repeatedly consistent, that is as close to proving cause and effect as they get.

Now, with Parkinson's, this medical detective work has edged closer to proving the case than with almost any other human ailment. In most patients, scientists say, Parkinson's is a disease with environmental origins.

For almost two centuries, since English physician James Parkinson described a "shaking palsy" in 1817, doctors have been baffled by the condition. In most people, a blackened, bean-size sliver at the base of the brain -- called the substantia nigra -- is crammed with more than half a million neurons that produce dopamine, a messenger that controls the body's movements. But in Parkinson's patients, more than two-thirds of those neurons have died.

After decades of work, researchers are still struggling with many unanswered questions, such as which chemicals may kill dopamine neurons, who is vulnerable and how much exposure is risky. Expressed in legal terms, pesticides are not guilty beyond a reasonable doubt -- but there is a substantial, and rapidly growing, body of evidence, many scientists say.

Though it's too late for some, scientists are confident they'll soon be able to predict who is vulnerable to environmental assaults on their brains. "That would be the Holy Grail for us," Miller said. "To actually pinpoint people at risk of this disease and protect them."