To the Editor I read with great interest the article by Richardson and colleagues1 showing that the diagnosis and severity of Alzheimer disease (AD) were both associated with elevated serum levels of dichlorodiphenyldichloroethylene (DDE), the main metabolite of dichlorodiphenyltrichloroethane (DDT). The authors also showed that DDE and DDT increase the release of amyloid precursor protein in cultures of human neuroblastoma cells, which gives a mechanistic plausibility to their observations, although this effect (amyloid precursor protein release increased by almost 50%) was found at DDE/DDT levels more than 1 order of magnitude greater than in patients with AD. I think these findings should be interpreted with caution. The main reason is that they were based on DDE serum concentrations that were not adjusted for several important confounders.
Bernard A. Elevated Serum DDE and Risk for Alzheimer Disease. JAMA Neurol. 2014;71(8):1055-1056. doi:10.1001/jamaneurol.2014.432