MONDAY, Feb. 3, 2014 (HealthDay News) -- Researchers say they've identified a number of common pesticides that increase the risk of Parkinson's disease, and that they've also discovered that people's genes can affect their level of risk.

In a previous study, the University of California, Los Angeles team found that exposure to a banned pesticide called benomyl increases the risk of Parkinson's. In this new study, the researchers said they identified 11 other pesticides that increase that risk.

The pesticides inhibit an enzyme called "aldehyde dehydrogenase" (ALDH). It converts compounds called aldehydes -- which are highly toxic to brain cells that produce a chemical called dopamine -- into less harmful compounds.

A lack of dopamine causes the tremors, limb stiffness and loss of balance experienced by people with Parkinson's disease, according to the U.S. National Institute of Neurological Disorders and Stroke.

The UCLA researchers also found that people with a common variant of the ALDH2 gene are particularly vulnerable to these ALDH-inhibiting pesticides, according to a university news release. People with the variant are two to six times more likely to develop Parkinson's than those without the variant when exposed to the pesticides.

The levels at which the pesticides inhibit ALDH are much lower than those at which they are currently used, according to the study in the Feb. 5 online issue of the journal Neurology.

It included 360 people with Parkinson's and 816 people without the disease who lived in three central California counties with high levels of agricultural production.

"We were very surprised that so many pesticides inhibited ALDH and at quite low concentrations, concentrations that were way below what was needed for the pesticides to do their job," study author Jeff Bronstein, a professor of neurology and director of movement disorders at UCLA, said in the news release.

"These pesticides are pretty ubiquitous, and can be found in our food supply and are used in parks and golf courses and in pest control inside buildings and homes. So, this significantly broadens the number of people at risk," he added.

Although the study found an association between exposure to certain pesticides and higher risk of Parkinson's disease, it did not establish a cause-and-effect relationship.