Parkinson's Disease

Parkinson’s Disease: What Causes It?

Deep inside the brain, in an area of the brain called the basal ganglia, are nerve cells that normally control a person’s voluntary movement and coordinate changes in person’s posture.

• When the brain sets in motion an action that results in lifting an arm, for instance, the basal ganglia signals and transmits messages to the other parts of the brain.
• Those messages are forwarded as electrical impulses along and between nerve pathways by the chemical messenger called dopamine, which is made in the area of the brain called the substantia nigra. The message passes on to the basal ganglia and down the spinal cord to the muscles used to lift the arm.

The basal ganglia are normally rich with this chemical called dopamine which has been delivered from a nearby area in the brain called the substantia nigra where the dopamine is manufactured.

In people with Parkinson’s, the nerve cells in the substantia nigra (where the dopamine is made) die, and the surviving cells do not produce enough dopamine.

The symptoms of Parkinson’s will begin when 80 percent of dopamine production from this area of the brain is lost.

We do not know why some previously normal nerve cells die causing dopamine levels to fall.

Parkinson’s is known to occur in some families, (10 percent to 15 percent of Parkinson’s disease may be inherited) and several genes have been identified in the last decade that appear to be associated with Parkinson’s and undoubtedly more will be discovered as research continues. However, not all familial Parkinson’s disease is inherited and in these cases it may occur as a result of a shared environment and a common susceptibility.

When Parkinson’s disease is inherited, it tends to occur in people under fifty years of age. (reference : Tanner and co-authors – Journal of American Medical Association. 1999 Jan 27;281(4):341-6). However, this does not mean that everyone who develops Parkinson’s under the age of fifty has inherited the disease.

The majority of people with Parkinson’s have what is called ‘sporadic’ disease, which means it occurs in the absence of a family history with no known cause.

Researchers feel that there may be more than one cause of Parkinson’s disease. (reference: ‘Parkinson’s is not one Disease’ by Dr D B Calne in ‘Parkinsonism and Related Disorders’ 7 (1): 3-7, 2000)

There is renewed interest in the possibility that a virus might be one cause of Parkinson’s. Parkinson’s was a complication of the influenza pandemic that occurred after World War 1. This virus disappeared in the early 1930s, before it could be identified. Animal studies support this, and two studies studies (reference: J. K. C. Tsui, and co-authors. Occupational risk factors in Parkinson’s Disease. Canadian Journal of Public Health 90 (5):334-335, 1999., and Tanner and co-authors) in humans showed that Parkinson’s is much more common in people who work and live in close contact with others.

The most recent study involved confirmed earlier findings that teachers and members of the medical profession carry twice the risk. The last study found no increase in Parkinson’s in welders.

A recent study described three statistically significant ‘clusters’ of people who worked together and who developed Parkinson’s within a similar time frame.One involved 4 members of a TV cast and crew (4 subjects out of 120) one a group of professors (4 subjects out of 30) and one a group of people in the office of a garment factory (3 out of 7). The authors do not speculate on the cause but each group worked in an environment with artificial ventilation.(reference: A Kumar and co-authors: Clustering of Parkinson’s Disease: Shared Cause or Co-incidence? Archives.Neurol.61 (7):pages 1057-1060, 2004)

There are still some scientists who think that “free radicals” may contribute to the damage to the nerve cells. These are toxic substances made in the body as a result of normal chemical reactions. Some people with Parkinson’s have increased levels of iron in the brain, which is part of the oxidation process. The implication of these findings is unclear. The use of vitamin E in Parkinson’s as a putative ‘free radical trapping’ agent is no longer recommended; indeed a recent study from the UK suggests that mega doses of vitamin E may be toxic.

In some cases, the cause is known.

• Parkinsonism can be a consequence of some medications (used to treat psychiatric illness or control nausea ).
• A small group of people developed Parkinsonism as a result of a known toxin called MPTP, found in an illegal synthetic opiate-derivative street drug and sold in California in the early 1980s.