A serious neurological disease in Pacific islanders, which is gradually disappearing with the arrival of the modern fast-food diet, appears to be caused by the toxic seeds of a local plant once widely used for food and medicine, according to a study.

The disease, once common among the Chamorro population of the islands of Guam and Rota, has many symptoms similar to those of Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis.

ALS, also called Lou Gehrig's disease, is a severe disorder of nerves that control muscle movement. The relationship between the plant toxin and the Pacific illness could provide an important clue to the role of environmental triggers in these three conditions.

The plant is the false sago palm, Cycas circinalis L., whose seeds are ground into flour by the Chamorro to make traditional foods and remedies. Cycad seeds were a staple in times of deprivation, including the Japanese occupation of Guam in World War II, according to Peter S. Spencer, director of the Institute of Neurotoxicology at Albert Einstein College of Medicine and the study's principal author.

Spencer said previous research on the Pacific islanders' disease had ruled out genetic and viral causes for the disorder, which can produce weakness or stiffness, loss of muscle control and dementia, and has been known to develop in islanders decades after they left their homeland.

Spencer said he and his coworkers first showed that BMAA, an amino acid found in cycad seeds, was toxic to nerve cells taken from the spinal cords of mice.

In the new study, they fed varying doses of BMAA to macaque monkeys for several weeks and looked for signs of neurological disease.

After a few weeks, monkeys developed muscle weakness, clumsiness, tremor, abnormal posture and a decrease in normal aggressive behavior. Exposure to BMAA for about three months produced "periods of immobility with an expressionless face" and a slow, shuffling gait -- symptoms similar to those of Parkinson's disease.

Microscopic examination showed a pattern of damage to nerve cells of the brain and spinal cord that control muscle movement.

Spencer said the findings, published in the July 31 issue of Science, encourage the view that ALS, Parkinson's disease and Alzheimer's may result from environmental toxins "operating on areas of the nervous system which, in and of themselves, are subject to age-related loss."