In America’s heartland, the connection between agricultural pesticides and a heightened risk for Parkinson’s disease is as clear as spring water.

Past scientific study has shown that even low-level exposures to such chemicals is associated with a 70 percent increased risk for developing the neurodegenerative disease, aside from greater possible risk for dementia, according to a 2006 study published in the Annals of Neurology. Now a new look at farm country shows greater incidence of Parkinson’s among some residents but not others — those with a variation of the ALDH2 gene. The study also finds that pesticides increase Parkinson’s risk, too, by inhibiting the aldehyde dehydrogenase enzyme, which helps to rid cells of toxins.

People with a specific variation of that ALDH2 gene were two to five times as likely to develop Parkinson’s, says Jeff M. Bronstein, an investigator from the University of California and the Greater Los Angeles Veterans Affairs Medical Center.

"These results show that ALDH inhibition appears to be an important mechanism through which pesticides may contribute to the development of Parkinson's disease," Bronstein said in a statement. "Understanding this mechanism may reveal several potential targets for preventing the disease from occurring or reducing its progression."

In the study, Bronstein compared 360 people with Parkinson’s with another 816 residents of the same area, using a computer model to incorporate information on pesticide exposures at home and work with information from the state’s department of pesticide regulation. For the first time, he and his colleagues determined that 11 pesticides inhibited the ALDH gene variant, all of which are used in farming. The 11 chemicals fall into four basic classes including dithiocarbamates, imidazoles, dicarboxymides, and organochlorides.

Some chemicals were more dangerous than others with regard to Parkinson’s risk, the researchers found. Workplace and residential exposures to the pesticide benomyl brought an associated 65 percent, whereas dieldrin brought a risk of six-fold. Those unfortunates exposed to three or more pesticides were 3.5 times more likely to develop the disease, overall.

Interestingly, the heightened risk for those with the altered ALDH gene came only with pesticide exposure. "In other words, having this gene variant alone does not make you more likely to develop Parkinson's," Bronstein said. "Parkinson's is a disease that in many cases may require both genetics and environmental factors to arise."

To lower risk for Parkinson’s, Bronstein said investigators might focus on reducing pesticide exposures while seeking to improve the enzymatic functioning of ALDH.

 

Source: Bronstein JM. Fitzmaurice AG, Rhodes SL, Cockburn M, Ritz B. Aldehyde dehydrogenase variation enhances effect of pesticides associated with Parkinson disease. Neurology. 2014.