Parkinson's disease (PD) is a progressive movement disorder. PD is characterized by:

  • Slowing down of movements (bradykinesia)
  • Tremor at rest
  • Muscle rigidity
  • Loss of reflexes that maintain posture and equilibrium

Part of the Brain Affected by PD—Yellow Section
Substansia Nigra
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PD is caused by a loss of certain nerve cells in the brain. The loss of these cells causes a decrease in the amount of a brain chemical called dopamine. Low dopamine levels cause PD symptoms.

The brain cells may be lost because of genetic defects, the environment, or some combination of the two. A small amount of people with PD have an early-onset form. This type is caused by an inherited gene defect.