What causes Parkinson's Disease?

There is much debate on exactly what causes Parkinson's disease. Heretofore, it was commonly thought that Parkinson's disease was caused by one or more environmental factors. However, for over a century there have been reports from researchers of families where Parkinson's appears to be inherited. The current theories try to take into account a number of possible causes for Parkinson's disease and Parkinsonism.

Aging

Because the common symptoms of Parkinson's are due to the decrease of dopamine producing cells in the substantia nigra (literally translates as 'black substance'), one school of thought is that Parkinson's disease is a part of the normal aging process. Since it is most prevalent in older people, this theory has some credence. It has been estimated that most adults lose approximately 9%-13% of those cells per decade of life. If this is the case the average adult would have lost 70%-80% of their original store of those cells by the age of 80 years. It has also been reported that the onset of symptoms of Parkinson's disease occurs when approximately 80% of the cells in the substantia nigra have been lost.

Environmental Issues

In the 1980s, scientists discovered a potent neurotoxin, MPTP, which was the byproduct of illegal drug production. Exposure to MPTP greatly accelerated the death of cells in the substantia nigra of those people who were exposed to it. There have been several other neurotoxins identified since then which carry a similar report. Some studies suggest that the onset of Parkinsonism (symptoms of Parkinson's Disease which may or may not be caused by true Parkinson's Disease) may be accelerated by exposure to one of these neurotoxins or others like them.

One substance that is being studied in connection with Parkinson's disease is manganese. In a study that took place at the University of California Santa Cruz, researchers exposed rats with a condition called pre-Parkinson's to low levels of manganese. The result was a marked acceleration of symptoms that was unrelated to an increased death of substantia nigra cells. They theorize that environmental factors that injure other areas of the brain may contribute an additive effect and worsen the symptoms of those who are susceptible to Parkinsonism.

Exposure to pesticides and insecticides can increase the risk of developing Parkinson's in people who have a susceptibility to this type of damage. However, the exact pesticides have not yet been identified.

Genetics

It has been noted that in about 5-10% of cases of Parkinson's disease, there is a family history of Parkinson's. The incidence of Parkinson's may be in the same generation - two siblings - or over two generations - a father and son, for instance. The suggestion that there is a hereditary factor to the disease is supported by the fact that the frequency of Parkinson's in non-Caucasian groups is very low. In addition, studies of families reveal a clear relation between the incidence of young-onset Parkinson's disease and a family history of Parkinson's.

Earlier studies, which originally suggested no connection between family genetics and Parkinson's, are now being reevaluated in light of more recent research.

In 1997, researchers discovered a mutation in chromosome 4 in one particular gene that appears to be related to the onset of Parkinson's disease. Since then, scientists have identified other genes and gene mutations that may contribute to a susceptibility to damage to the substantia nigra.

Medication

It is a little known fact in the general public that a number of medications can cause Parkinson's like symptoms. These include Haldol and Thorazine, which are used to treat psychiatric disorders, Reglan and Compazine, which are used to treat nausea, and Depacon, used to treat epilepsy. It is important to understand that these symptoms are short-term and reversible, usually disappearing within a few weeks after stopping the medication.