Disease, Parkinson: A slowly progressive neurologic disease characterized by a fixed inexpressive face, a tremor at rest, slowing of voluntary movements, a gait with short accelerating steps, peculiar posture and muscle weakness, caused by degeneration of an area of the brain called the basal ganglia, and by low production of the neurotransmitter dopamine. Most patients are over 50, but at least 10 percent are under 40.
Treatment is by medication, such as levodopa (Larodopa) and carbidopa (Sinemet). A surgically implanted device that helps control the shaking has recently become available. In some cases, surgery on the globus pallidus or thalamus has proved helpful.
A rare early form of Parkinson disease is due to mutation in chromosome 9. whereas people with the usual late form of the disease tend to have mutations in chromosome 17. From a genetic viewpoint it is now clear that Parkinson's disease is heterogeneous; it is not one, but several diseases. Gene mutations appear involved in all forms of Parkinson disease.