The idea was simple, chilling, and controversial: Chamorro people on Guam who feasted on a traditional delicacy, the giant fruit bat, may have ingested enough of a toxin to develop a rare and fatal neurodegenerative disorder. Now this hypothesis, aired last year, has been given a boost. In the 12 August issue of Neurology, researchers report that museum specimens of Guam's fruit bats, also known as flying foxes, are chock-full of the neurotoxin BMAA.
For decades scientists have struggled to explain a high incidence on Guam of a motor-neuron disease that combines hallmarks of amyotrophic lateral sclerosis and the dementia of Parkinson's, with symptoms ranging from uncontrolled trembling to paralysis. One leading hypothesis linked the illness to consumption of the seeds of the cycad plant. These are used to make tortilla flour and contain BMAA and another neurotoxin, cycasin. Residents can remove most of the toxins, however, by thoroughly washing the seeds.
Last year ethnobotanist Paul Cox, director of the National Tropical Botanical Garden in Kalaheo, Hawaii, noted that another local specialty, Guam's giant fruit bats, love to eat cycad seeds and suggested that cycad neurotoxins could have accumulated to dangerous levels in the bat flesh (ScienceNow, 29 March 2002). But the evidence was only circumstantial: More bats were killed and eaten on Guam immediately after World War II, when guns became readily available, coinciding with a peak in incidence of the neurodegenerative disease.
Now Cox and ethnobotanist Sandra Banack of California State University, Fullerton, have the first hard evidence for their theory. Examining skin tissue from three 50-year-old Guam bats from a museum at the University of California, Berkeley, they found concentrations of BMAA hundreds of times higher than in cycad flour. Cox says he was "stunned." The pair now plans further research on how variations in the bats' diet influence BMAA levels to better understand cycad biomagnification.
"The research seems to answer a lot of the questions we've all had about Guam disease," says John Stein, a motor neurophysiologist at the University of Oxford, U.K. He hopes the study will prompt scientists hunting for the cause of various neurodegenerative disorders to "look for more common [environmental] toxins that might be similar to BMAA."