From Scientific American:
As its 19th-century name suggests–and as many people know from the educational efforts of prominent Parkinson’s sufferers such as Janet Reno, Muhammad Ali and Michael J. Fox–the disease is characterized by movement disorders. Tremor in the hands, arms and elsewhere, limb rigidity, slowness of movement, and impaired balance and coordination are among the disease’s hallmarks. In addition, some patients have trouble walking, talking, sleeping, urinating and performing sexually.
These impairments result from neurons dying. Because the insights involve molecules whose activity could potentially be altered or mimicked by drugs in ways that would limit cell death, the discoveries could lead to therapies that would do more than ease symptoms–they would actually limit the neuronal degeneration responsible for disease progression.
More here.