What Causes Parkinson's?
To date, despite decades of intensive study, the causes of Parkinson’s remain unknown. Many experts think that the disease is caused by a combination of genetic and environmental factors, which may vary from person to person.
In some people, genetic factors may play a role; in others, illness, an environmental toxin or other event may contribute to PD. Scientists have identified aging as an important risk factor; there is a two to four percent risk for Parkinson’s among people over age 60, compared with one to two percent in the general population.
The chemical or genetic trigger that starts the cell death process in dopamine neurons is the subject of intense scientific study. Many believe that by understanding the sequence of events that leads to the loss of dopamine cells, scientists will be able to develop treatments to stop or reverse the disease
Read more below about each of these:
The vast majority of Parkinson's cases are not directly inherited. About 15 to 25 percent of people with Parkinson’s report having a relative with the disease. In large population studies, researchers have found that people with an affected first-degree relative, such as a parent or sibling, have a four to nine percent higher chance of developing PD, as compared to the general population. This means that if a person’s parent has PD, his or her chances of developing the disease are slightly higher than the risk among the general population.
Researchers have discovered several gene mutations that can cause the disease directly, but these affect only a small number of families. Some of these mutations involve genes that play a role in dopamine cell functions. Parkinson’s has developed at an early age in individuals with mutations in genes for parkin, PINK1, LRRK2, DJ-1, and glucocerebrosidase, among others.
Because genetic forms of a disease can be studied in great detail in the laboratory, and because understanding the rare genetic forms of Parkinson's may help us to understand more common forms of the disease, genetics is currently the subject of intense research.
Some scientists have suggested that Parkinson's disease may result from exposure to an environmental toxin or injury. Epidemiological research has identified several factors that may be linked to Parkinson’s, including rural living, well water, manganese and pesticides.
Some studies have demonstrated that prolonged occupational exposure to certain chemicals is associated with an elevated risk of PD. These include the insecticides permethrin and beta-hexachlorocyclohexane (beta-HCH), the herbicides paraquat and 2,4-dichlorophenoxyacetic acid and the fungicide maneb. In 2009, the US Department of Veterans Affairs added Parkinson’s to a list of diseases possibly associated with exposure to Agent Orange.
A synthetic neurotoxin agent called MPTP can also cause immediate and permanent parkinsonism. The compound was discovered in the 1980s in individuals who injected themselves with a synthetic form of heroin contaminated with MPTP. Cases of MPTP-induced Parkinson’s in the general population are exceedingly rare.
It is noted that a simple exposure to an environmental toxin is never enough to cause Parkinson’s. Most people exposed to a toxin do not develop the disease. In fact, there is no conclusive evidence that any environmental factor, alone, can be considered a cause of the disease.
However, environmental factors have been helpful in studying laboratory models of Parkinson's. Scientists continue to pursue these clues to understand why Parkinson’s disease occurs.
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