What Causes Parkinson's Disease?

The cause of Parkinson’s Disease has been a matter of some controversy. Until recently, it was generally accepted that Parkinson’s Disease was caused by one or more environmental factors, though there have been reports from researchers for over a century of families where Parkinson’s appears to be inherited. The current theories take into account a number of possible causes for Parkinson’s Disease and parkinsonism.

Normal Aging

Since the symptoms of Parkinson’s are due to the decrease in dopamine producing cells in the substantia nigra (literally translates as ‘black substance’), one avenue of thought is that Parkinson’s Disease is, at it’s most basic, a part of the normal aging process. Since it is most prevalent in older populations, this theory has some credence. It’s estimated that most adults lose approximately 9%-13% of those cells per decade of life. That would mean that the average adult would have lost 70%-80% of their original store of those cells by the age of 80. It’s been noted that the onset of symptoms of Parkinson’s Disease is generally when approximately 80% of the cells in the substantia nigra have been lost.

Environmental ‘Insults’

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. There have been a number of other neurotoxins identified since then with a similar effect. Many researchers believe 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 of the substances 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.

It’s also been shown that exposure to pesticides and insecticides can increase the risk of developing Parkinson’s in people who have a susceptibility to damage, but specific pesticides have not been identified.

Genetics – Is PD Inherited?

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 genetic component to the disease is supported by the fact that the incidence of Parkinson’s in non-Caucasian groups is very low. In addition, studies of families showed a clear connection between the incidence of young-onset Parkinson’s disease and a family history of Parkinson’s. Twin 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 seems 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

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, used to treat nausea, and Depacon, used to treat epilepsy. These symptoms are short-term and reversible, usually disappearing within a few weeks after ceasing the medication.