Parkinson's Disease (PD) is a disorder of the central nervous system. It was first described in 1817 by Sir James Parkinson, a British physician.

It is generally considered a disease of advanced age, however is it estimated that 15% of all PD patients are 50 years of younger. About 1.2 million persons in the USA have PD. The disease progresses from diagnosis to major disability over 10 - 20 years.

Although the exact cause or causes of PD are not known, researchers have discovered that symptoms occur when certain cells in the brain either die or become impaired and are no longer able to supply a key neurotransmitter (a chemical known as "dopamine") to the part of the brain that controls movement, balance and walking. The brain can compensate for some loss of dopamine, but as the dopamine-producing cells continue to die off and the dopamine level falls below about 20% of normal, patients develop symptoms.