Parkinson's disease is a progressive disorder caused by degeneration of nerve cells in the part of the brain that controls movement.

What is going on in the body?

Parkinson's disease involves a breakdown of the nerve cells in the motor area of the brain. As the cells break down, there is a shortage of dopamine. Dopamine is a neurotransmitter, or chemical that carries messages to the body. When there is a shortage of dopamine, the messages that regulate movement aren't sent properly.

What are the causes and risks of the disease?

The cause of Parkinson's disease is not known. There may be a hereditary tendency to the disease that is worsened by factors in the environment. Some people with Parkinson's disease have an abnormality on chromosome 4.

There is evidence that Parkinson's disease may be caused by a defect in the body's normal methods for breaking down protein. This defect allows debris to build up in the brain and damage brain cells. The defect may be caused by one or more of the following factors:

The symptoms of Parkinson's disease usually begin at about age 60. It is most common in people in their 70s and 80s. Parkinson's disease is twice as frequent in men than in women. Preliminary research suggests that estrogen, a female hormone, may protect against Parkinson's disease.