Health A-Z

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What Is It?

Parkinson's disease (PD) is a disease of the central nervous system. It causes problems with body motions, including:

  • Tremor (shakiness)

  • Rigidity (muscle stiffness)

  • Slowed body movements

  • Unstable posture

  • Difficulty walking

PD develops when certain nerve cells (neurons) in the brain die. These are neurons that produce a chemical called dopamine. Dopamine helps relay messages between areas of the brain that control body movement.

When these neurons die, abnormally low levels of dopamine are produced. This makes it difficult to control muscle tension and muscle movement.

PD usually occurs in middle age. It typically begins around age 60. A small number of patients have early onset PD. They are younger than 40 years old when symptoms begin.

Having a parent or sibling diagnosed with the disease at a younger age increases your risk of getting PD. The same is not true if the affected family member was older when diagnosed.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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