Parkinson\u27s disease (PD) is the second most common neurodegenerative disease after Alzheimer disease, having an annual incidence of approximately 20 per 100,000 people (Schapira 2004, Fischer 1999). An estimated one million persons in the United States have PD, and this prevalence is likely to rise as the population ages (Schapira 2004). This disorder is characterized pathologically by a loss of dopamine neurons in the substantia nigra pars compacta that produces the neurotransmitter dopamine. The clinical features of PD are motor function abnormalities including tremor, rigidity, slowness of movement, and difficulty with balance. In the early stages of PD, treatments may help to control symptoms, but over time the disease progresses with the development of symptoms such as freezing, falling, autonomic dysfunction, and dementia (Schapira 2004). While the cause of PD is unknown, genetic susceptibility and environmental factors seem to be associated with the disease based on epidemiologic and laboratory studies. Among the environmental risk factors, exposures to pesticides have been researched as a possible cause of PD. This focus on pesticides was sparked by the discovery that a chemical metabolite, similar in structure to the pesticide Paraquot, caused PD-like symptoms in heroin users who were exposed to a synthetic impurity of the drug (Li 2005)
