A colonoscopy or similar test could one day diagnose Parkinson's disease years before symptoms occur. That's because signs of Parkinson's that appear in the brain also show up in the colon, a new study says. Researchers examined tissue samples obtained during colon exams of people who later developed Parkinson's disease. The samples were taken several years before the patients showed symptoms of the neurological disorder… Parkinson's disease is caused by loss of brain cells that produce dopamine, a brain chemical needed to control muscle movement. One change that occurs in the brains of Parkinson's patients is the formation of clumps called Lewy bodies. The protein alpha-synuclein is found in all Lewy bodies, according to the Mayo Clinic.