The symptoms of Parkinson's disease may have been identified as early as 5000 B.C. This chronic and progressive brain condition occurs when there is a loss of cells in a part of the brain that controls movement. This loss causes a deficiency of dopamine (a chemical in the brain), which causes the characteristic movement problems of Parkinson's disease. This disease can be difficult for healthcare providers to diagnose, as the early symptoms may be vague and can mimic other conditions. In many cases, symptoms of Parkinson's disease may even be dismissed as normal aging.