A person with Shy-Drager syndrome has an abnormally functioning autonomic nervous system. The autonomic nervous system controls many involuntary functions of the body, including blood pressure and heart rate.
Shy-Drager syndrome is somewhat similar to Parkinson's disease, but causes more extensive damage in the body. There is widespread degeneration of many parts of the autonomic nervous system, which controls involuntary activities of the body such as blood pressure.
The exact cause of Shy-Drager syndrome is not known. It is more common in people older than 60 years and occurs more frequently in males.