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Recent decline in incidence rates of ALS in Guam and the Kii Peninsula of Japan strongly implicates environmental factors rather than inheritance in its causation. Environmental studies in Western Pacific foci showed identical mineral compositions in the soils and drinking water, i.e., extremely low calcium (Ca) and magnesium (Mg) and high aluminum (Al) and manganese (Mn). Series of trace-elemental analyses of the CNS tissue of ALS patients have revealed a high contents of Al and Ca with significant positive correlations between Al and Ca and/or between Ca and Mn, suggesting the prolonged exposure to these trace environment to cause abnormal mineral metabolism detrimental to neurons. Using electron energy loss spectrometry (EELS), Al was found to accumulate within DNA-containing chromatins and rRNA-containing cellular components, i.e., nucleolus, heterochromatin, rough endoplasmic reticulum, in lumbar motor neurons of ALS. Thus, Al may preferentially bind to nucleic acids and cause a progressive inhibition of the protein synthesis of rRNA and the transcription or gene modulation of DNA, leading to neuronal degeneration.

The decline in the high incidence of amyotrophic lateral sclerosis, parkinsonism, and Alzheimer-type dementia among the Chamorro population of the western Pacific islands of Guam and Rota, coupled with the absence of demonstrable viral and hereditable factors in this disease, suggests the gradual disappearance of an environmental factor selectively associated with this culture. One candidate is seed of the neurotoxic plant Cycas circinalis L., a traditional source of food and medicine which has been used less with the Americanization of the Chamorro people after World War II. Macaques were fed the Cycas amino acid beta-N-methylamino-L-alanine, a low-potency convulsant that has excitotoxic activity in mouse brain, which is attenuated by N-methyl-D-aspartate receptor antagonists. These animals developed corticomoto-neuronal dysfunction, parkinsonian features, and behavioral anomalies, with chromatolytic and degenerative changes of motor neurons in cerebral cortex and spinal cord. In concert with existing epidemiological and animal data, these findings support the hypothesis that cycad exposure plays an important role in the etiology of the Guam disease.