February 6, 2014
News Review From Harvard Medical School -- Gene, Pesticides Linked to Parkinson's Risk
People who have a variant gene and are exposed to certain pesticides may have a higher risk of Parkinson's disease, a new study finds. Researchers tested a variety of pesticides. They found that several of them interfere with the function of an enzyme called ALDH. This enzyme helps to break down chemicals that kill brain cells involved in making dopamine. People with Parkinson's disease have too little dopamine. Researchers asked about exposure to pesticides among people who were part of a study of Parkinson's risk in 3 California farming counties. In all, 360 people had Parkinson's and 816 people did not. Some people had a different (variant) version of a gene that provides instructions for making ALDH. Researchers looked at Parkinson's rates in people exposed to the pesticides that interfere with ALDH. Those with the variant gene were 2 to 5 times as likely to develop Parkinson's disease as those without the gene. The increase in risk varied for different pesticides. The journal Neurology published the study online February 5. HealthDay News wrote about it.
By Robert H. Shmerling, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Parkinson's disease is a disease of the central nervous system that slowly gets worse. Symptoms include:
- Stiff or rigid legs, arms and trunk
- Balance problems
- Loss of coordination
Over time, these symptoms tend to become more and more disabling. They can have a devastating impact on those with Parkinson's disease and their loved ones.
The cause of Parkinson's disease is unknown. Experts writing about the condition put it this way:
"While the cause of Parkinson's disease is still unknown, remarkable advances have been made in understanding the possible underlying mechanisms." (UpToDate)
"Scientists looking for the cause… continue to search for possible environmental factors, such as toxins, that may trigger the disorder, and study genetic factors to determine how defective genes play a role." (National Institute of Neurological Disorders and Stroke)
"The cause of PD is still unknown. Researchers think that both genes and environment may play a role." (The American Academy of Neurology)
With so much mystery, it's no wonder that news about a possible trigger of Parkinson's disease is a big deal.
A new study suggests that people with certain genes may be prone to developing Parkinson's disease if they are exposed to pesticides. The latest edition of the medical journal Neurology published the study. Researchers compared 360 people with Parkinson's disease with 816 people who did not have it.
Using a computer model of pesticide exposure in different rural regions of California, the researchers found that:
- Exposure to certain pesticides at home and at work increased the risk of Parkinson's disease. The increase varied from 65% to 600% for different pesticides.
- Exposure to more than one pesticide was linked to a higher risk of Parkinson's disease.
- People with a particular gene variant who also were exposed to these pesticides were 2 to 5 times as likely to develop Parkinson's disease. However, having the gene without pesticide exposure did not increase disease risk.
The gene studied in this research provides instructions to the body for making an enzyme called aldehyde dehydrogenase (ALDH). This enzyme helps to break down alcohol and other toxins. The pesticides studied interfere with ALDH. So this research suggests that impaired production or function of ALDH -- due to the luck of your genes plus pesticide exposure -- might contribute to the development of Parkinson's disease. This discovery could lead to preventive measures and new treatments.
Interestingly, these findings follow a report just last week about pesticides and another condition. That study linked DDT exposure to brain changes found in Alzheimer's disease.
What Changes Can I Make Now?
At the current time, there is no reliable way to prevent or cure Parkinson's disease.
However, this new research suggests that avoiding pesticide exposure might reduce your risk of developing the disease. You can take these steps to reduce exposure:
- Use methods other than pesticides to deal with pests. For example, clear away brush or standing water that encourage pests to nest and breed.
- If you do use pesticides, follow directions carefully.
- Use only products that are developed specifically for the pest you are fighting.
- Wear protective clothing and gear, as recommended on the product's label.
- Store and discard pesticides properly.
Treatment can reduce symptoms of Parkinson's disease. So, if you have worrisome symptoms, see your doctor.
What Can I Expect Looking to the Future?
This latest research is not the last word on the cause of Parkinson's disease. In fact, it raises several questions:
- Can measures to reduce pesticide exposure actually lower the risk of Parkinson's disease?
- How can ALDH (or its function) be increased in people who carry the high-risk gene variant described in this study?
- Do pesticides in non-farm settings (such as home use) carry similar risks related to Parkinson's disease? This new study looked only at exposure to pesticides used in farming.
- What other factors contribute to the development of Parkinson's disease? Some people with the high-risk ALDH gene and pesticide exposure did not develop the disease. So there are probably other triggers yet to be discovered.
- Are other brain diseases, including Alzheimer's disease, caused by toxin exposure?
You can expect researchers to address these questions by conducting more research in the near future.