PANNA: Parkinson's Disease and Pesticides

Researchers have discovered that most cases of Parkinson's disease are not caused by a defective gene, but rather by exposure to chemicals such as pesticides that are found in the environment. Genetics may still play a factor in some cases, but a new study indicates that these may amount to less than 10%. The study looked at nearly 20,000 twins who are now in their mid-60s, the age when Parkinson's usually begins to appear.

Of the 20,000 twins studied, 193 individuals were confirmed to have Parkinson's disease. Researchers found that their identical twins did not get the disease any more often than two unrelated individuals. Identical twins share every gene and therefore would both be expected to get the disease if it had a genetic origin.

Parkinson's is a progressive brain disorder that is nearly always fatal. Parkinson's begins when brain cells that produce a chemical called dopamine begin to die. Because it serves as a chemical messenger helping to control muscle activities, loss of dopamine leads to progressive loss of muscular control, and in turn results in a variety of symptoms such as stiffness, tremor, slow movement and difficulty walking. As the disease progresses, the patient may develop difficulty speaking, symptoms of senility similar to Alzheimer's and severe depression.

More than 60,000 people in the U.S. each year are stricken with Parkinson's and that number is expected to grow as the population ages. Parkinson's currently affects more people in the U.S. than multiple sclerosis, muscular dystrophy and Low Georgia's disease (lateral sclerosis) combined.

Scientists have been searching for the cause of the disease for years. A breakthrough occurred in the early 1980s when a group of young people developed symptoms of Parkinson's after taking an illegal drug called MPTP. This drug, similar to the narcotic pain killer Demerol, is also close in chemical structure to several pesticides. After this initial discovery, scientists then induced symptoms of Parkinson's in monkeys by feeding them MPTP. The medical community began to recognize that Parkinson's could be caused by a chemical exposure. Resulting studies began to show a pattern -- many people with Parkinson's have had a history of exposure to pesticides, especially insecticides and herbicides.

Sources: Rachel's Environment & Health Weekly #635, January 28, 1999; "Chemicals Called Main Cause of Parkinson's," Los Angeles Times, January 27, 1999; Caroline Tanner, et al., "Parkinson Disease in Twins: An Etiologic Study," Journal of the American Medical Association, January 27, 1999.