What casues Parkinson's?

Causes
What causes Parkinson's?
Why an individual develops Parkinson's disease remains unclear. The cause is probably a combination of genetic and environmental factors, and may vary from person to person. Although the cause of Parkinson's remains unknown, scientists have identified factors that contribute to Parkinson's in some patients. For example, people over age 60 have a two-to-four percent risk of developing Parkinson's disease, compared with the one-to-two percent risk in the general population.
Below is information on the two factors that scientists think are most likely to cause Parkinson's disease.
Genetics About 15 to 25 percent of people with Parkinson's report having a relative with the disease. In large epidemiological studies (studies that deal with incidence, distribution and control of disease in a population), researchers have found that people with an affected first-degree relative, such as a parent or sibling, have a two-to-three fold increased risk of developing Parkinson's, as compared to the general population. This means that if your parent has Parkinson's, your chances of developing the disease are slightly higher than the risk in the general population.The vast majority of Parkinson's cases are not directly inherited, but researchers have discovered several genes that can cause the disease in a small number of families. Some of these genes involve proteins that play a role in dopamine cell functions. 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 disease may help to understand more common forms of the disease, genetic aspects of PD are currently the subject of intense research.
Environmental Factors 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 PD, including rural living, well water, herbicide use and exposure to pesticides. Also, a synthetic narcotic agent called MPTP can cause immediate and permanent parkinsonism if injected. These environmental factors are not useful in diagnosing the cause of Parkinson's disease in individual people. In fact, there is no conclusive evidence that any environmental factor, alone, can be considered a cause of the disease. However, these environmental factors have been helpful in studying laboratory models of Parkinson's disease. Scientists are continuing to pursue these clues to establish more concrete linkages.
Most experts share the opinion that Parkinson's is caused by a combination of genetic and environmental factors. However, no one yet knows what this combination is. For more information on genetic and environmental factors in causing Parkinson's disease, read the PDF News & Review article Nature Versus Nurture: What Causes PD?