Parkinson's Disease is a chronic, disabling illness that has affected between 500,000 to 1.2 million people in the United States. Cells that produce the neurotransmitter dopamine in the brain die and do not regenerate in people with PD. As a result, people with Parkinson's Disease suffer from a range of symptoms involving muscle movement. These symptoms may include tremors, problems with walking and balance, rigid muscles, an immobile facial expression, and diminished speaking volume. Sometimes cognitive diffi culties develop.