- Parkinson's disease is a progressive disorder of the nervous system
- Neurons die, leaving the brain with a deficit of a chemical called dopamine
- Approximately 1 million people in the United States have Parkinson's
(CNN)Parkinson's disease is a "progressive disorder of the nervous system," according to the Mayo Clinic, that primarily affects a patient's movement. It often starts with a small tremor in the hand or muscle stiffness and gets worse over time. There is no test for Parkinson's, so it is occasionally misdiagnosed.