Parkinson's disease (PD) is a progressive degenerative disease of the central nervous system, affecting individuals in adult life. It is a chronic condition that usually develops in people over the age of 50, and there are around 50 000 new cases each year in the United States. The pathology is a specific pattern of nerve cell (neuronal) degeneration in a region of the brain called the substantia nigra, as well as in other regions that control movement. It creates a shortage of the brain-signalling chemical (neurotransmitter) known as dopamine, resulting in impaired movement. Degenerating neurones in PD characteristically deposit intracellular structures known as Lewy bodies, thought to be altered cytoskeletal elements, which accumulate due to neuronal damage. The symptoms of PD include slowness of movements and reflexes (bradykinesia), muscular rigidity, resting tremor and difficulty with balance and walking. There is at present no specific biological test for...