The Parkinson's Mystery

Even as a large European study reinforces links between Parkinson's disease and genetics, head injury, pesticide exposure and other potential causes, the disease's specific origins remain a mystery.

Researchers at Aberdeen University in Scotland worked with those in Italy, Sweden, Romania and Malta to look at the life histories of 959 patients suffering from Parkinson's and 1,989 patients who were not to try and tease out the possible causes for the disease.

They found that having close family members with Parkinson's increased an individual's risk for the disease by five times, being knocked unconscious more than once increased the risk two and a half times and having high pesticide exposure in work or hobbies made someone 33 percent more likely to contract Parkinson's.

The study was published this week in the Journal of Occupational and Environmental Medicine.

"It's a solid study, [but] it has the limitations of many studies of this type," said Harvey Checkoway, an epidemiologist at the University of Washington who was not involved with the research.

Parkinson's is the second most common degenerative brain disease, following Alzheimer's, afflicting around 1 million Americans, including 1 percent of all Americans above the age of 60.

The World's Most Famous Parkinson's Patient

Parkinson's supposed link to head injury is most commonly associated with three-time heavyweight boxing champion Muhammad Ali, who was diagnosed in 1983, nearly two years after his retirement from the sport.

But many experts dispute the connection.

"I'm a little lost to understand why they believe that is related to his head injuries," said Thomas Hammeke, co-chief of the neuropsychology division at the Medical College of Wisconsin.

He said that the rate of Parkinson's disease for boxers has not been shown to be any higher than for other professions. He added that football players, despite often suffering multiple concussions, have not been shown to suffer widely from the disease.