Enfield — Researchers with Dartmouth-Hitchcock Medical Center have identified a potentially significant cluster of Lou Gehrig’s disease cases around Mascoma Lake.

Working with a team of other researchers, they are trying to determine if the cluster, and smaller ones like it in New Hampshire, Vermont and Maine, can be linked to certain algae blooms that produce a neurotoxin that may trigger the disease. They also noted that the link, if one can be found, would likely involve long-term exposure to the neurotoxin by people with a genetic predisposition to the disease, officially known as amyotrophic lateral sclerosis, or ALS.

Nine people living near Mascoma Lake have been diagnosed with ALS since 1990, all but one between 2000 and 2006. Three of them were in 2006, according to Elijah Stommel, a DHMC neurologist who has been mapping cases of the disease in New Hampshire, Vermont and Maine.

“There’s clearly a cluster of ALS around that lake,” Stommel said in a phone interview yesterday. “I want to be really clear that we don’t have any strong link at this point … I don’t think there’s any cause for alarm.”

ALS is a progressive, often fatal neurodegenerative disease that attacks nerve cells in the brain and spinal cord, leading to muscle weakness and atrophy, according to the ALS Association.

The incidence of ALS in the United States is about two per 100,000 people. The Dartmouth team has determined that the incidence of ALS cases can double for people living near waterways with cyanobacteria blooms.

The Mascoma Lake prevalence is about 25 times greater than national norms, he said.

Three cases of ALS also were mapped near Kennedy Pond in Windsor, Stommel said.

“We’ve found a few hotspots in Vermont as well,” he said.

Stommel — collaborating with researchers from University of New Hampshire, the Wyoming-based Institute for Ethnomedicine and the New Hampshire Department of Environmental Services — hopes to determine whether the ALS cases near Mascoma and other smaller clusters are related to outbreaks of cyanobacteria.

Cyanobacteria are photosynthetic, single-celled organisms that commonly occur in New Hampshire and Vermont lakes and ponds. But the bacteria can colonize in nutrient-rich or warm waterways, forming a blue-green scum on the water surface, according to the DES Web site.

The suspected ALS trigger is the neurotoxic amino acid Bmaa (B-Methylamino-L-alanine), which can be produced by cyanobacteria and has been found in the brain samples of ALS patients, and other people with neurodegenerative diseases, in recent studies.

The researchers are applying for a federal grant from the National Institute of Environmental Health Sciences to analyze water, hair and other samples from clusters in northern New England that could prove the suspected link.

“At this point we are really just beginning the research. We are really interested in Dr. Stommel’s findings. We think they are very important,” said Paul Cox, the executive director of the ethnomedicine research institute in Jackson Hole, Wyo.

Cox, who has conducted groundbreaking work on Bmaa, said “a small percentage of the population” might be vulnerable to the neurotoxin, but that most others may be able to metabolize or excrete it.

“The hypothesis is that in those people it can trigger neurodegenerative diseases, including ALS,” Cox said. “Most people probably would not be affected by it at low concentrations.”

Stommel also emphasized that there is no need for public alarm.

“I don’t think that people overall should be terribly panicked, because you probably need a genetic predisposition,” he said.

The Dartmouth and DES teams have saved water and other samples from the areas of concern and are collecting more, to determine if Bmaa was present.

Stommel said brain and spinal cord tissue samples from some of the ALS patients who died would also be analyzed for the study.

Jody Connor, the limnology center director for DES, said researchers also might analyze hair samples from dogs and humans that have been in waters infected with cyanobacteria.

“There are still a number of things we are trying to work through. Anything we think can show some links, we’ll be looking at that,” he said.

Connor and others also noted that Mascoma Lake is far cleaner than it was in the 1960s and 1970s, when the state had to treat it regularly for sewage.

“Since that time the lake has cleared up significantly,” he said.

News of the possible link, first reported in the New Hampshire Sunday News, prompted concern from officials in Enfield.

Phil Neily, the building and health inspector in Enfield, said there have been no confirmed cyanobacteria blooms on the lake this year, but that historically some residents with camps along the lake tapped it for domestic water uses.

“I know there were lines directly into the lake,” Neily said. “I’d like to see the research and I need to know more about it.”

Cyanobacteria exposure is believed to potentially occur through a variety of means, including drinking, showering, swimming, boating or eating fish from infected waters.

Enfield Town Manager Steve Schneider also said he wanted to learn more.

“It’s alarming, I guess, if it turns out to be true,” Schneider said. “…It may have been a result of the health of the lake 20 or 30 years ago. Who knows?”

Meanwhile, cyanobacteria outbreaks continue to occur in the region.

Connor, the DES lakes-quality expert, said Goose Pond in Canaan was posted Friday with a cyanobacteria warning after the bacteria was found there. A similar warning was issued for Harvey Lake in Northwood, N.H., yesterday.

Residents are advised not to swim, drink or wade in the water if they see any blue-green scum, and all pets should be kept out of the water until the warnings are lifted.