A medical mystery in Guam
By Chelsie Vandaveer
May 31, 2004
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Cycads, those plants in the Order: Cycadales, comprise three families, eleven genera, but only around 200 species worldwide. Typically subtropical or tropical, cycads are seed-bearing plants with a lineage that dates back to the Mesozoic. Depending on the species, cycads grow anywhere from open, dry, rocky, nutrient-poor soils to moist shady forests. Generally considered slow-growing, cycads manufacture a high quality starch and store it with their caudexes (trunks) and seeds.
People all over the world used cycad starch as a supplement to their diets. In Africa, the starch was extracted from Encephalartos stems. In 1834, Johann Lehmann even named the genus from the Greek words, encephalos, meaning brain (or pith), and artos, meaning bread, referring to the use of the starch from the caudex for making flatbread.
In Australia and the Pacific Islands, people extracted the starch from the seeds of Cycas. In Mesoamerica, seeds of Zamia were used. Both seeds and trunks of Zamia provided the starch in the Caribbean and in Florida, the Tequesta and later the Seminoles took the starch from the stems of the coontie (Zamia pumila Linnaeus). Cycads are highly toxic containing an azoxyglycoside, either cycasin or macrozamin, and an amino acid, beta-methylamino-L-alanine (BMAA). BMAA is closely related to the amino acid BOAA which causes lathyrism. (See Plants that Changed History, January 14, 2003)
Domesticated animals—sheep, horses, cattle, and dogs--that eat cycads suffer from an irreversible neurological disorder called the "zamia staggers" or severe gastrointestinal distress and liver damage. But native animals that feed on the seeds or leaves are not affected. Aboriginal peoples learned to separate the toxins from the starch.
After World War II, a medical mystery arose on Guam. The Chamorro people were suffering from amyotrophic lateral sclerosis (ALS or 'Lou Gehrig's disease') at 100 times the rate of the rest of the world. Sufferers were labeled, raput, "lazy" when in reality their bodies and minds slowly wasted away.
The disorder now called ALS-PDC has a confusing array of symptoms similar to ALS, Parkinsonism-dementia, and Alzheimer's. The disease has been linked to the cycad toxins, but which toxin and how much, since most of the toxins are removed in the processing. And people in other parts of the world eat the starch and the effects are not seen in those populations.
Two hypotheses have come forward. Knut Norstog suggests that pollen from the Cycas may be to blame. The pollen contains both toxins and Cycas on Guam produce heavy loads of pollen. Inhaled pollen may allow the toxins to cross from the nasal tissues to the brain.
Paul Alan Cox and Oliver W. Sacks hypothesize a case of biomagnification (bioaccumulation). Native animals eat the plant or its seeds with impunity, but the toxins build up in the animal's body. The animal in Guam is the flying fox or fruit bat (Pteropus mariannus). These mammals feast on the sarcotesta, the fleshy outer seed covering. The Chamorro feast on a delicacy—flying foxes.
Wikipedia, the free encyclopedia has information about Megachiroptera, the flying fox or fruit bat (Pteropus mariannus). To view his website, click on the link:
http://en.wikipedia.org/wiki/Flying-fox
(Compiled from: "This Obscure Malady", Terence Monmaney, Annals of Science, The New Yorker, Oct. 29, 1990; "Aboriginal Preparation of Cycas Seeds in Australia", Wendy Beck, Economic Botany, NYBG, April-June, 1992; "Cycasin and its mutagenic metabolites", Robin W. Morgan and George R. Hoffmann, Mutation Research, Elsevier Biomedical Press, 1983; "The Ubiquity of Cycasin in Cycads", P. DeLuca, A. Moretti, S. Sabato, and G. Siniscalco Gigliano, Phytochemistry, Pergamon Press, 1980; "Toxicity of Cycads", Marjorie Grant Whiting, Economic Botany, NYBG, Oct-Dec, 1963;
"Cycad Toxicity", Nadia Audhali and Dennis Stevenson, The Cycad Pages, Royal Botanic Garden, Sydney; "Cycad neurotoxins, consumption of flying foxes, and ALS-PDC disease in Guam" Paul Alan Cox, PhD and Oliver W. Sacks, MD, Medical Hypothesis, Neurology, 2002; Cycads of the World, David L. Jones, Smithsonian Institution Press, 1993)
Suggested Reading:
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What plant cannot exist without a bat? Weird Plants - October 18, 2001
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