Possible involvement of overexposure to environmental selenium in the etiology of amyotrophic lateral sclerosis: A short review

Excess exposure to the metalloid selenium (Se), a trace element with both toxicologicaland nutritional properties, has been implicated in the etiology of a human motor neuron diseaseof unknown origin and extremely severe prognosis, sporadic amyotrophic lateral sclerosis (ALS).This relation has been suggested on the basis of two epidemiologic investigations which found anincreased risk of ALS associated with residence in a seleniferous area or with consumption of drinkingwater with unusually high levels of inorganic hexavalent Se, in South Dakota and in northernItaly respectively. Biological plausibility to a Se-ALS relation is provided by veterinary medicineobservations and toxicological studies, showing that Se, particularly the inorganic forms, has a selectivetoxicity to motor neurons in swine and in cattle. Neurotoxic effects of Se species have also beendemonstrated in laboratory studies and, for the inorganic forms, even at very low concentrations.Selenium has also been shown to affect muscle function in experimental animal models. Overall,these findings from the epidemiologic and the toxicological literature indicate that environmental Se,particularly in its inorganic forms and at unexpectedly low levels of exposure, might be a risk factorfor ALS, suggesting the opportunity to further investigate this issue.