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Pesticide exposure might be linked to higher Alzheimer's risk

Tuesday January 28, 2014
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An increased risk for Alzheimer’s disease appears to be associated with elevated blood levels of a byproduct of the pesticide DDT, which was banned in the U.S. in 1972 but is used for agriculture in other countries, according to a study.

Alzheimer’s disease is the most common neurodegenerative disease in the world and the number of cases is expected to increase, according to background information in the study, which was published Jan. 27 on the website of JAMA Neurology.

Risk factors for late-onset Alzheimer’s disease (after age 60) are not completely understood but include environmental and lifestyle factors. Having a version of a gene, an apolipoprotein E4 (APOE4) allele, also appears to increase risk.

Jason R. Richardson, PhD, of the Rutgers Robert Wood Johnson Medical School and Environmental and Occupational Health Sciences Institute, Piscataway, N.J., and colleagues examined the association between Alzheimer’s disease and blood levels of DDE (dichlorodiphenyldichloroethylene), which is the metabolite of the pesticide DDT (dichlorodiphenyltrichloroethane), and whether the APOE genotype has an effect on that association.

The researchers used existing blood samples from 86 Alzheimer’s disease patients and 79 controls. The DDE found in blood samples is likely due to its long half-life and continued exposure from food imported from other countries where DDT is still used or from legacy contamination of soil and waterways in the U.S., according to the researchers.

DDE was detected in the blood of 70% of control and 80% of Alzheimer’s disease patients, and their DDE levels were associated with increased risk for Alzheimer’s disease. Average levels were 3.8 times higher in the blood of Alzheimer’s disease patients, according to the study results.

Scores on a test of cognitive function (the Mini-Mental State Examination) were lower in the group with the highest levels of DDE who carried the epsilon-4 version of the APOE gene compared with those carrying another version.

“Elevated serum DDE levels are associated with an increased risk for AD and carriers of an APOE4 Ɛ4 may be more susceptible to the effects of DDE,” the authors wrote. “Identifying people who have elevated levels of DDE and carry an APOE Ɛ4 allele may lead to early identification of some cases of AD.”

Study abstract: http://archneur.jamanetwork.com/article.aspx?articleid=1816015


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