Medical Health Encyclopedia

Late Onset PD. Two landmark studies published in the Journal of the American Medical Association provided the first evidence of a genetic link to late-onset Parkinson’s disease. In these 2001 studies, researchers found that regions on chromosomes 5, 6, 8, 9, and 17 were implicated with Parkinson’s. The parkin gene (located on chromosome 6) and the tau gene (located on chromosome 17) were both found in families that had late onset Parkinson’s. Parkin was previously thought to be responsible only for early-onset Parkinson’s, but this research identified it in families that had both early- and late-onset disease forms. These studies also bolstered the theory that Parkinson’s does have a genetic component and is not caused solely by environmental factors. A 2005 study found that a G2019S mutation in the LRRK gene, located on the PARK8 region of chromosome 12, was definitively associated with late-onset Parkinson’s disease in North American and European families .

Environmental Assaults and Oxygen-Free Radicals

Environmental toxins, infections, and other triggers can provoke excessive production in the body of oxygen free-radicals, damaging particles that may play a major role in the deterioration of nerve cells that lead to Parkinson's.

Infectious Agents. Some research has identified immune factors that suggest a viral presence in the Lewy bodies and swollen nerve pathways of Parkinson's brains. Influenza and other potent viruses have long been known to be a cause of parkinsonism. In one well-known example, a major flu epidemic causing encephalitis in the early twentieth century left many of its victims with parkinsonism.

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Environmental and Industrial Chemicals. Intense exposure to certain environmental and industrial chemicals is also being studied.

• Pesticides and Herbicides. Some evidence implicates pesticides and herbicides as important factors in many cases of Parkinson's disease. A higher incidence of parkinsonism has long been noted in people who live in rural areas, particularly those who drink private well water or are agricultural workers. A large 2000 study found a strong link between high exposure to insecticides and herbicides at home and a 50% to 70% increase in risk of Parkinson's.
• Other Chemicals. Intense exposure to other industrial chemicals and metals (manganese, copper, lead, iron, mercury, zinc, aluminum, and others) has also been linked with parkinsonism, which is often reversible. The role of long-term exposure in the development of Parkinson's disease is unclear. High levels of iron content observed in critical parts of the brain in PD are under particular scrutiny.

Aging Process

Most, but not all, Parkinson's victims are elderly. Some studies indicate that the very elderly are not susceptible to the disease, indicating that the aging process itself is not the major player in the disease. Aging does appear to reduce the concentration of dopamine in structures called dopamine transporters, which carry the neurotransmitter back and forth between nerve cells. Some researchers posit that any excessive stress on these transporters might trigger Parkinson's disease in the aging, and more vulnerable, brain.