Persistent environmental pollutants may be a modifiable risk factor associated with amyotrophic lateral sclerosis (ALS), results from a cohort study indicate.
Development of ALS may be associated with a combination of genetic susceptibility and toxic exposures. Based on geographic variations in ALS death rates in Michigan, Eva Feldman, MD, PhD, of the Alfred Taubman Medical Research Institute at the University of Michigan, and colleagues hypothesized that environmental toxins may be associated with ALS.
The researchers conducted a case-control study of ALS patients at a tertiary referral center in Michigan to assess the association between ALS and environmental and occupational toxin exposures. Exposures were assessed with surveys and blood analysis for 122 persistent environmental pollutants. The study included 156 participants with ALS (mean age of 60.5 years; 61.5% male) and 128 healthy controls. Complete data was available for 101 participants with ALS and 110 controls.
A significant association was found between reporting pesticide exposure during the cumulative exposure window and ALS development (OR: 5.09, 95% CI: 1.85-13.99, P=.002). A history of military service 10 to 30 years prior (OR: 2.18, 95% CI: 1.01-4.73, P=.049) or ever (OR: 2.31, 95% CI: 1.02-5.25, P=.046) was also found to be associated with ALS.
Blood analysis demonstrated greater odds of ALS with exposure to a brominated flame retardant (BFR) (polybrominated diphenyl ether 47, OR: 2.69, P=.001), 2 polychlorinated biphenyls (PCBs) (PCB 175, OR:1.81, P=.005 and PCB 202, OR: 2.11, P=.001), and 2 organochlorine pesticides (OCPs) (pentachlorobenzene, OR: 2.21, P=.04 and cis-chlordane, OR: 5.74, P=.005).
In an accompanying editorial, Jacquelyn Cragg, PhD, of the Department of Environmental Health at Harvard T.H. Chan School of Public Health in Boston and colleagues note that the use of occupational histories and industrial hygienist helped to eliminate sources of potential bias. They also point out that the study may be limited by education levels and one-time measurements that may not represent lifetime exposure.
“The comprehensive assessment of 122 different toxins in blood by Su and colleagues is an important strength of the study. This allows an unprecedented ability to consider exposure mixtures and to attempt to identify compounds that are truly related to ALS rather than simply correlated with something else that is,” they wrote. “Overall, the results of Su and colleagues are an important effort in the quest to better understand the role of environmental and occupational exposures in the development of ALS.”