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Vital Signs

Lakeside ALS cluster draws attention but is still unexplained

An unexplained cluster of ALS cases around scenic Mascoma Lake generated a flurry of press coverage this summer.

By Jennifer Durgin

Blooms of algae are usually dismissed by most lake-goers in New Hampshire and Vermont as nothing more than slimy, unpleasant nuisances. But this past summer, the blooms gained a more menacing reputation when some nascent Dartmouth research about a possible link between blue-green algae and Lou Gehrig's disease received prime-time media coverage.

The hullabaloo began in May, when Dr. Tracie Caller, a neurology resident at Dartmouth and one of the researchers studying the relationship, presented some preliminary findings at a workshop for the New Hampshire Volunteer Lake Assessment Program.

Risk: "We weren't out promoting our own work," says Caller, just sharing what her research group-led by a DHMC neurologist, Dr. Elijah Stommel-had learned so far. They'd found that the risk of developing Lou Gehrig's disease, or amyotrophic lateral sclerosis (ALS) as it is officially known, seemed to be 10 to 25 times greater than average in several small towns near Mascoma Lake in Enfield, N.H. From 2000 to 2006, eight people living near the lake were diagnosed with the disease, which is quite rare nationally (there are only about two cases per 100,000 people each year).

Stommel's group has identified smaller clusters around other New England lakes, too. But "we don't know if the blooms are actually causing the disease or just happen to be by chance related," Caller is careful to point out. "Things cluster by chance in nature anyway."

Nuances: Such nuances were lost when the Union Leader, New Hampshire's statewide newspaper, reported the findings on June 7 in an article titled "NH lake linked to ALS cases." More newspapers, as well as television and radio stations, covered the story in the weeks that followed and, to varying degrees, attempted to convey the uncertainty of the findings.

ALS is a progressive disease that destroys nerve cells in the brain and spinal cord. Motor neurons, which control muscle movement, degenerate, causing weakness and paralysis. Only about 10% of people with ALS have a family history of the disease, according to the ALS Association. In the other 90%, the cause is unknown, though many theories exist, says Caller.

One theory is that exposure to a neurotoxin called BMAA, which is produced by some species of blue-green algae, may trigger ALS. The most compelling evidence for this theory comes from studies in Guam, where rates of neurodegenerative diseases are fairly high, natives consume a diet high in BMAA, and BMAA has been found in the brains of people who've died from such diseases.

Neurons: Furthermore, BMAA can cause motor neurons to die in cell cultures, explains Caller, and it works through the same biological pathways as one of the medications used to treat ALS.

So far, Caller, Stommel, and their collaborators have not found BMAA in any of the algae they've tested from New Hampshire lakes, including Mascoma. But that doesn't mean BMAA is never present. "It seems like most species that we test can make the toxin," says Caller, "but they don't always. We don't know if there is something that has to trigger it."

Paper: A scientific paper detailing what the researchers have found-or not found-is due to be published this fall, but there's still a lot more work to be done before a link between blue-green algae and the ALS clusters can be confirmed.

Based on what's known now, Stommel told the local paper, the Valley News, "I don't think there's any cause for alarm."

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