As the disease progresses, it may cause muscle stiffness and rigidity on one or both sides of the body. More severe cases make walking difficult, and sometimes the disease restricts a patient's mobility almost completely. However, mental capacity is not affected until the later stages, and this occurs in only about a third of all cases. Cause Medical researchers still do not know exactly why in Parkinson's disease the brain cells begin to degenerate.
Dopamine is a neurotransmitter, a substance involved in transmitting nerve impulses.
Usually the amount of dopamine is in balance with a different neurotransmitter, acetylcholine. Parkinson's disease upsets that chemical balance in the nervous system, giving rise to the various symptoms associated with the disorder. Another disorder, called Parkinsonism, produces symptoms that are essentially the same as those of Parkinson's disease, since dopamine production is also reduced. Incidence Parkinson's disease afflicts about 1 million people in the United States. It usually begins between the ages of 45 and 65.