Parkinson's disease is a disorder of the brain, but new research suggests the gut and bowel may play a much bigger role than anyone thought.

Parkinson's is a progressive condition that is characterized by tremors or shaking, and difficulties with walking and co-ordination. While it's unclear what causes the disease, it is characterized by the accumulation of a protein called "alpha-synuclein" in brain cells, which kills the cells.

The disease can't be definitively diagnosed until after a patient's death, when an autopsy can reveal alpha-synuclein. So for living patients, there is no test; most diagnoses are made by taking a thorough history of symptoms.

But scientists, led by Dr. Kathleen M. Shannon, a neurologist at Rush University Medical Center in Chicago, have stumbled upon what could be an early warning sign of the disease: abnormal chemicals in the colon that can be found two to five years before Parkinson's symptoms even begin.

"It sounded kind of wacky to us when we started out, that we were looking at the intestines. But everything we have done has been in the positive direction," Shannon told CTV News.

"This is the first time that anyone has shown that the abnormal Parkinson's protein have been found in any tissue before the disease has been diagnosed," she said.

Shannon believes that nerve cells in the intestines might also be affected by Parkinson's, especially since symptoms such as constipation frequently precede movement disorders.

Shannon's team published two papers in the journal Movement Disorders this week, in which they offered evidenced for their theories.

In the first study, 10 patients with early Parkinson's disease underwent a procedure in which a flexible scope was inserted into their lower bowels to take tissue samples.

The researchers observed abnormal levels of alpha-synuclein in the biopsied tissues from nine of the samples (the 10th sample was unsuitable for study), but not in samples from 23 healthy subjects and 23 subjects with inflammatory bowel disease.

In the second study, they examined biopsy samples from three Parkinson's patients who had undergone a colonoscopy two to five years before the diagnosis of Parkinson's. All three showed the characteristic levels of alpha-synuclein.

The findings not only raise the prospect for a test to diagnose Parkinson's, they also raise questions about whether Parkinson's might begin in the gut before toxins spread to the brain.

"Recent clinical and pathological evidence supports the notion that Parkinson's disease may begin in the intestinal wall then spread through the nerves to the brain. Clinical signs of intestinal disease, such as constipation, precede Parkinson's disease diagnosis by more than a decade," said Shannon.

Dr. Anthony Lang, from the Movement Disorders Program at Toronto Western Hospital, thinks there might be something to it.

"We have reason to believe that part of the nervous system outside the brain is involved and in fact, may be involved very early, even before the brain is affected," he says.

This might lead Parkinson's researchers into an entirely new direction, as they try to answer whether a colonoscopy could become an early warning test.

"This study gives a basis of hope that we may be able to make a diagnosis several years before the patient presents with the clinical features," says Lang.

At the moment, there are few treatments for Parkinson's. By the time symptoms appear in most patients, they have already lost 60 to 80 per cent or more of dopamine-producing cells in their brain.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip