What Causes Parkinson's Disease?

Parkinson's is caused by a loss of nerve cells in an area of the brain called the substantia nigra. These cells are responsible for releasing dopamine, a substance that transmits signals between substantia nigra and other parts of the brain that are responsible for co-ordinating movement.

The symptoms of Parkinson's appear when 60-80% of dopamine has been lost.

We don't yet know what causes these brain cells to malfunction although a number of possible causes have been put forward:

• Genetics. The chances of someone developing the disease is increased if a first-degree relative (parent, child or sibling) has it. This would suggest a genetic component in the formation of this condition but we still don't know whether genetic make-up plays a major or minor role.
• Environmental factors. Exposure to high levels of herbicides, pesticides and fungicides is known to increase the risk of developing Parkinson's although it is not known whether this is a primary or secondary cause. Iron is also considered a factor because of the high levels of iron in people with Parkinson's
• Medication. The following drugs can cause the symptoms of Parkinson's if taken for long periods or at excessive dosages- haloperidol, chlorpromazine and metoclopramide. None of these drugs actually cause the disease to develop and the symptoms will disappear when the drugs are stopped.
• Lewy bodies. These are unusual deposits or clumps of the protein alpha-synuclein that occur in the braincells of people with Parkinson's disease. However it is not clear whether these are damaging the cell or protecting it from other harmful proteins.

• Viruses. It has been thought that there is a link between Parkinson's and viral infection, especially after many people who developed encepholopathy after the 1918 influenza epidemic went on to develop progressive Parkinson's.
• Head trauma. Recent studies have shown some correlation between previous head injury and the development of Parkinson's which would appear to indicate that people who have had a serious head injury are much more likely to develop Parkinson's.

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