The Neurotoxic Effects of Cycads and Metals: A Review

Abstract

The bioaccumulation of environmental toxins as possible risk factors in the etiology of amyotrophic lateral sclerosis and parkinsonism-dementia complex (ALS/PDC) is studied in three foci of the Western Pacific: Guam, the Kii Peninsula, and West Papua New Guinea. The objective of this study was to evaluate the best evidence on the exogenous causes of ALS/ PDC, with emphasis on the role of cycads, iron, and manganese in the Western Pacific foci, by performing a systematic review of major electronic databases using predefined criteria, 68 of which met the selection criteria . Two major environmental hypotheses are associated with this enigmatic disease: the vegetal hypothesis, which focuses on the neurotoxic and genotoxic properties of the cycad, and the mineral hypothesis, which focuses on the neurotoxic properties of metals . Although typically studied independently, environmental data suggests these two hypotheses may, in fact, converge . Epidemiologic research investigating the association between exposure to environmental toxins and ALS/PDC has proven inconclusive . Nevertheless, possible causal links indicate a need for more holistic research to not only better understand ALS/PDC, but also glean new insights regarding the associated neurodegenerative diseases .