[Disappearance of ALS from Guam: implications for exogenous causes].
The author reports the disappearance of amyotrophic lateral sclerosis (ALS) from Guam over past 30 years, which coincided with rapid changes in the ecology, socioeconomy, and westernization of the life style. This slow but steady decline is believed to be the consequences of radical changes from food collection to wage-based life style and dietary improvement in recent years and elimination of exogenous factors. Those risk factor(s) are believed to be the environmental trace metals which must have triggered the accelerated oxidative stresses in the motor neurons of genetically susceptible population. Changing Epidermiology: 1. The annual incidence of 70/100,000 in 1960s down to 7/100,000 in 1990s, and remained unchanged for past 15 years. 2. Upward shift of age at onset by 10 years and at death by 8 years and even out of sex ratio. 3. Birth cohort analysis showed less risks for those born after 1920. No ALS cases born after 1945. 4. No increase in the incidence of ALS among non-Chamorros transients of Guam and Marianas during W.W.II. 5. Long-term resident non-Charmorro and half-Chamorros on Guam are also affected. 6. Charmorro migrants to U.S. Mainland are affected after long absence from Guam. 7. Incubation period for both ways is estimated to be 18 approximately 20 years. 8. Other forms of dementias like Alzheimer disease (AD) and vascular dementias are on the rise and the leading cause of death is cerebro- and cardiovascular diseases. 9. ALS is also declining in past 10 approximately 15 years in Kii peninsula, and West New Guinea. Changing Ecology of Guam: 1. One third of Island land was used for construction of huge military bases after W.W.II. 2. Urbanization of villages including concrete houses, deep well water supply, sewage, and electrification. 3. Tourism boom: high-rise hotels, development of 7 golf courses and other recreational facilities resulted in loss of flora and erosions of soil. Socioeconomic Changes: 1. Shift in population demography; Efflux of Chamorros and influx of aliens; Chamorros less than 50% by 1990. 2. Tourists passed 1 million in 1994. 3. Automobiles 1 car/1.5 person. 4. Westernization: After W.W.II, almost free access to Military Commissary for imported food and appliances. 5. Life style: from food collection to wage-based society. Genetic Studies: 1. Familial aggregations, but no clear-cut Mendelian inheritance. 2. Segregation analysis: no absolute genetic or environmental cause but additive gene component may play a role in genetic susceptibility and basis for geographical clustering. 3. Absence of Apo-E or Mu/Zn SOD genes. 4. Recent discovery of mtDNA Complex I deficiency in Parkinsonism-dementia cases suggests mitochondrial DNA abnormality. Comparative Environmental Studies: 1. Environmental studies in three hyperendemic areas in the Western Pacific--Kii, Marianas, and west New Guinea, where strikingly high incidences of ALS is known to occur, found the identical geochemical environment--low Ca, Mg, and Zn and high A1, Mn, Fe, Si, in the garden soil and drinking water. 2. Exogenous etiologic factors that are absent from primitive culture of Auyu and Jackai tribes in West New Guinea were eliminated. 3. Cycad neurotoxicity has been excluded. 4. Suspected exogenous agents that are common in these 3 hyperendemic areas are (a) locally grown vegetables, starchy roots, and reef fish; (b) surface water containing soluble organic minerals from red laterites; (c) rain water that is chemically pure and lack of essential minerals. Pathogenic Speculation: Chronic dietary deficiency since birth in Ca, Mg and Zn induced excessive absorption of divalent cations which accelerates oxidant-mediated neuronal degenerations in a genetically susceptible population. The process is probably carried through interactions between cytoskeletal abnormality of the neuron, aging process, abnormal proteins, and mitochondrial dysfunction.