An increased risk for Alzheimer disease (AD) appears to be associated with elevated blood levels of a byproduct of the pesticide DDT, which was banned in the United States in 1972 but is still used for agriculture in other countries, according to a study by Jason R. Richardson, Ph.D., of the Rutgers Robert Wood Johnson Medical School and Environmental and Occupational Health Sciences Institute, Piscataway, N.J., and colleagues.
AD is the most common neurodegenerative disease in the world and the number of cases is expected to increase. Risk factors for late-onset AD (after age 60 years) 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, according to the study background.
The authors examined the association between AD and blood levels of DDE (dichlorodiphenyldichloroethylene), which is the metabolite (a byproduct of metabolism) of the pesticide DDT (dichlorodiphenyltrichloroethane) and whether the APOE genotype has an effect on that association. Researchers used existing blood samples from 86 AD 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 study.
DDE was detected in the blood of 70 percent of control and 80 percent of AD patients and their DDE levels were associated with increased risk for AD. Average levels were 3.8 times higher in the blood of AD 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 Ɛ4 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 study concludes. “Identifying people who have elevated levels of DDE and carry and APOE Ɛ4 allele may lead to early identification of some cases of AD.”
(JAMA Neurol. Published online January 27, 2014. doi:10.1001/.jamaneurol.2013.6030.