
Medical researchers are not sure how Parkinsons disease starts. It may be caused by a combination of factors both inside the body (such as genetic factors) and from the environment (such as toxins). It is difficult to predict who will get Parkinsons disease.
Approximately 1 million people in the United States have Parkinsons disease. Most people who develop Parkinsons disease are 60 years old or older when the symptoms begin. Some people may develop Parkinsons disease at a younger age (for example, in their 30s, 40s, or 50s).