For decades, researchers had been flummoxed by a deadly illness suffered by as many as a quarter of the Chamorro people of Guam. Shortly after World War II, doctors began reporting that the people were coming down with a strange combination of Alzheimer’s, Parkinson’s, and ALS (or Lou Gehrig’s disease). The Chamorros themselves called it lytico-bodig, “listless paralysis.” They were suffering at a rate up to a hundred times higher than the rate of ALS elsewhere. Neurologists tried for five decades to identify the cause, ruling out genetics.
When Paul learned of the disease, he immediately thought of a possible trigger: flying foxes, giant fruit bats with wing spans reaching up to 5 feet. (Paul had studied their role in pollinating rain forests for his doctoral dissertation at Harvard.) He knew that they inhabited the island of Guam; that the bats eat vast quantities of seeds from cycads, a tropical plant that dates back to the dinosaurs; and that natives of the Pacific islands have been eating these bats for millennia. Perhaps a toxin in those seeds was bioaccumulating, building up in the bats the way pesticides do in the environment.
Neurologists hadn’t explored this relationship, so Paul did what comes naturally: He and two other scientists, Sandra Banack and Susan Murch, flew to Guam and talked to the Chamorros themselves. They wrote the names of local foods on 3-by-5 cards, and then asked the interviewees to sort the cards in order of their favorites. Flying foxes consistently landed at the top of the pile. Not only did the people eat bats, they said they were delicious.
For centuries, the bats had been a sustainable food, until Americans came to Guam after the war, bringing guns. Since the bats have no natural predators, they simply circled their home tree when startled by gunfire, making them easy to pick off. The Chamorros started consuming them in such numbers that soon the bats began to disappear.
Paul and his colleagues suspected that the flying foxes themselves weren’t to blame for the high rates of disease. The real source, they thought, lay in what the bats were eating. Cycad seeds contain high concentrations of an amino acid called BMAA, produced by cyanobacteria within the plant’s roots. Also known as blue-green algae, cyanobacteria have been around 3.5 billion years, growing in deserts, oceans, lakes, and even in some car radiators and air conditioning filters. They’re probably the chief reason our atmosphere changed two billion years ago, in what scientists grandly call the Great Oxygenation Event, enabling the evolution of oxygen-breathing species like flying foxes and humans.
But BMAA is also a potent neurotoxin; if taken in massive amounts, it can cause paralysis or death, while the more insidious effects happen slowly. To begin at the beginning of the food chain, it goes like this: The cycads live in synergy with cyanobacteria in the roots. Cyanobacteria produce BMAA, which gets taken up in the cycad seeds. Bats eat the seeds, concentrating the BMAA. Chamorros eat the bats.
Still: How could BMAA cause lytico-bodig?
As the bats vanished from Guam, the Chamorros began importing them from other islands. These imported bats, they confided to Sandra Banack, didn’t taste as good—nor did they contain high levels of BMAA. A decade or two after the native bats began declining, so did the disease.
Paul and Sandra reasoned that BMAA was causing a slow breakdown in the proteins of the central nervous system. Analysis of victims’ brain and nerve tissues had revealed the exact same defects as victims of ALS, Alzheimer’s, and Parkinson’s, including tangled-up proteins. (Medical researchers call them “tangle diseases,” and they’re related to a host of incurable neuronal ailments, including Lewy body dementia, Pick’s disease, and supranuclear palsy.) If the scientists could isolate the process behind lytico-bodig, then they just might find a hint at a remedy for one of them.
Possibly even all of them.