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When we think of the causes of Alzheimer's and other brain diseases, most of us don't think of algae. A toxic blue-green moss found all over England, Scotland, and Wales, however, seems to be the cause of an epidemic of Alzheimer's.

British health officials have sounded an alarm about rates of motor neuron diseases such as amyotropic lateral sclerosis (ALS or Lou Gehrig's disease, known in the UK as motor neuron disease), Alzheimer's disease, and dementia up to 25 times normal near certain lakes and reservoirs.

The common factor in over a million potential cases of degenerative brain disease in the UK alone is a chemical called beta-methylamino-L-alanine, or BMAA, an amino acid produced by certain kinds of algae.

How Can Pond Slime Cause Brain Disease?

The algae that make BMAA don't attack the brain directly, the way an infection might. Instead, they produce a toxin that can get into the human food supply. The sequence of steps runs like this:

  • Algae grows in still, fresh water in ponds and lakes during the summer months. Runoff that includes animal manure or nitrogen fertilizer helps it grow. 
  • The algae produces a the potent BMAA toxin. Both the algae and the toxin are consumed by other microorganisms, and by fish, that are in turn caught and eaten by humans.
  • In the human brain, BMAA gets incorporated into proteins in the same places that the brain would ordinarily use the amino acid serine. BMAA gives the protein an unusual shape, and the protein forms tangles that are characteristic of ALS, Alzheimer's disease, progressive supranuclear palsy, Parkinson's disease, and Lewy body disease. 

Although the pond slimes that produce BMAA are producing a major health crisis in Britain, scientists didn't begin to understand the disease there. The mystery of BMAA was actually unraveled after an epidemic of brain disease swept Guam.

An Epidemic of Brain Disease in the West Pacific

Guam has been an American territory since the end of the nineteenth century, but American doctors stationed on the island didn't notice a serious health problem until the 1950's. (Guam was occupied by Japan in World War II, and reconstruction tasks had taken priority until the 1950's.) Large numbers of the native Chamorro people developed an unusual kind of dementia that had features of both Alzheimer's and ALS.

The condition affected natives and Filipino immigrants to the island who adopted native culture, the Filipino immigrants not getting sick until they had been on the island for 10 years or more, but not people who stayed in American administrative quarters. It wasn't something in the air or the water or spread by mosquitoes. It was also something that was a lot worse in some places than in others. At the height of the outbreak in the 1950's, nearly every family in the fishing village of Umatac on the southern coast of Guam had at least one member who had the disease.

When the local medical examiner did autopsies, an unusual malformation known as neurofibrillary plaques, a kind of tangled protein, was noticed. There wasn't a clear pattern, however, in the development of the disease. Some people got it earlier in life, and some got it later. Native Chamorro people, the original inhabitants of the island, got the disease, while Japanese ex-pats living on the island and Americans at the military base did not. There had to be something affecting the native Guamanians that wasn't part of the everyday life of more recent arrivals.

A Batty Solution to a Medical Mystery

The culprit in the local diet turned out to be fruit bats. The native cuisine of Guam includes one ingredient most non-Pacific cultures shun, roasted whole "flying foxes," which are giant fruit-eating bats, without even the hair or guts removed. It's a local treat that even most American service members tend to shun. Fruit bats feed on local fruits, including the fruits of the cycad palm, which is another plant that makes the BMAA toxin. Finally, in 2015, experiments with animals confirmed that consuming the cycad fruit caused the disease.

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