A result of chance or the birth of an epidemic? In the village of Saint-Vaast-en-Chaussée, in the Somme, residents are wondering: no fewer than five cases of Charcot's disease have been detected in the same street in nearly twelve years. Usually, according to Public Health France (SPF), the incidence in our country of this pathology is 2.7 new cases per year per 100,000 inhabitants.
Amyotrophic lateral sclerosis (ALS), or Charcot disease, is a neurodegenerative pathology which manifests itself by progressive muscular paralysis due to degeneration of motor neurons, the cells which control muscle contraction. Incurable to date, its outcome is dramatic: life expectancy is on average three or four years after the onset of symptoms - although 10% of patients live more than ten years.
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Faced with this mystery, the mayor of Saint-Vaast-en-Chaussée contacted the Hauts-de-France Regional Health Agency (ARS), which contacted Public Health France. “Investigations are underway,” SPF confirms to Le Figaro. Their first objective is to carefully document the cases (...), an essential first step in the investigation of the “cluster” (an abnormally high number of cases of a pathology, within a time window and/or of place, editor’s note)”. “It is first a question of confirming the “superincidence” in time and space, then of searching, if necessary, for the existence of one or more local causes for this grouping of cases, other than chance. », continues SPF.
In fact, the causes of this disease are currently unknown in most cases. Only hypotheses prevail. However, we know that only 10% of cases are hereditary, and several risk factors have been noted such as physical activity, repeated blows to the head, or certain professions (agricultural work, military). How can we explain, then, that this rare disease likes to appear in “clusters” in certain villages or even certain streets? Are there other environmental causes of Charcot disease?
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Because the case of Saint-Vaast-en-Chaussée is not isolated. In France, other ALS “clusters” appeared in particular in Hérault, but also in a small town in Isère and a village in Savoie around fifteen years ago, leading doctors and local authorities to carry out investigations. Studies which have highlighted, in particular, two toxic agents: the neurotoxin BMAA, which is found in particular in cyanobacteria present in water, and hydrazine, a chemical substance which is found in mushrooms , false morels.
Thus, around fifteen cases of ALS have been recorded in twenty years in Bellentre, a Savoyard village of around 900 inhabitants. In 2009, a general practitioner was surprised to diagnose this disease for the third time in less than ten years and turned to Dr. Emmeline Lagrange, neurologist at Grenoble University Hospital, who found a fourth case and alerted the regional health agency. and Public Health France. No risk factors have been identified, but Dr Lagrange continues to see patients. Health authorities are investigating and confirming seven cases out of ten reported.
Researchers have in mind the famous “case” of the island of Guam, in the Pacific, where ALS was 50 times more common than elsewhere. The cycad nut, widely consumed locally, was finally implicated, or more precisely a neurotoxin it contains, BMAA. Also in the United States, this neurotoxin has been found in aquatic plants. This famous example in the scientific community is, however, nuanced by certain scientists, like Dr Philippe Couratier, head of the neurology department at Limoges University Hospital and leader of the rare diseases ALS and motor neuron diseases sector. The latter thus explained to Le Figaro in 2021 that it was not ALS strictly speaking, but syndromes associating the symptoms of ALS with Parkinsonian and cognitive disorders; Furthermore, if the cessation of nut consumption was accompanied by a drop in the incidence of the disease, BMAA has not been identified with certainty as the cause of this ALS epidemic.
In 2013, an epidemiological study published in the scientific journal Plos One, carried out on 381 patients who developed ALS in Hérault, however leaned in the same direction. The number of patients is in fact higher in the municipalities close to the Etang de Thau, an area of mussel and oyster production. However, the famous BMAA, produced by cyanobacteria found in the pond, is found in mussels and oysters from the pond. “Although it is not possible to certify a direct link between seafood consumption and the existence of this ALS cluster, these results add new data to the potential association of BMA with ALS,” concludes the study with caution.
Return to Savoy. A report from Public Health France was published in January 2017. Several environmental factors were scrutinized: drinking water, air, pollution, various toxicants, electromagnetic fields... but nothing emerged. Conclusion of SPF: this cluster could be the simple result of chance.
This annoys Professor William Camu, neurologist, member of the ALS reference center at Montpellier University Hospital and author of the study around the Etang de Thau. “The job of Public Health France is to say that there is nothing! Marisol Touraine (Minister of Health at the time, Editor's note) was ordered to say that there was nothing. The goal is not to make a wave,” he accuses, recalling the controversy over the late ban on oysters contaminated with norovirus at Christmas 2023 in the Arcachon basin, despite the alert from some doctors.
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Despite this report, Dr. Lagrange continues to investigate in Savoie with Professor Camu. A local health watch found 14 patients in total. For each person, a family tree going back four generations is drawn up; for ten of them, a genetic analysis is carried out. These studies tend to rule out blood ties and the genetic factor. Interviews were conducted with 13 patients or their relatives for those who died, and 48 healthy “witnesses”, living nearby, with similar profiles.
Exposure to lead, high voltage lines... multiple factors are studied, in vain. “There was only this very strange eating habit,” relates Dr. Lagrange: all the ALS patients consumed gyromitres, or false morels, often raw or very lightly cooked, keeping the cooking water. However, the false morel contains hydrazine, a chemical substance known for its toxicity - gyromitres are also banned for sale in France. And similar findings have been produced in the United States and Finland. The results of the study are published in the Journal of the Neurologic Sciences in August 2021. “It is very possible that this toxin is responsible for ALS,” insists Professor William Camu, co-signatory of this publication on false morels.
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But - and this is the difficulty of scientific research - the fruit of this delicate work remains a hypothesis. In addition, studies involving BMAA and hydrazine are nuanced by some scientists. “The problem with ALS is that even if it is the least rare of rare diseases, it remains a rare disease, so it is difficult to do in-depth epidemiological studies,” notes Séverine Boillée, research director at the ALS. 'Inserm and specialist in ALS at the Brain Institute in Paris (ICM).
The culpability of the BMAA in ALS “has not been proven”, decides the one who leads a research team on the causes of the pathology. This toxin “has not been found specifically in ALS patients. It has also been found in patients affected by other diseases.” What about false morels? “Even if genes were looked for”, it would have been necessary to carry out “a much more in-depth genetic analysis”, believes the researcher, and to be able to take “blood samples from all affected patients during their lifetime to be able to conclude”.
“There are more than thirty genes described in ALS, but no team is looking for all the genes in a patient. In sporadic forms only two genes are studied. We looked at the five most frequent genes even though none of the patients had a family history and none of them were related,” argues Dr. Lagrange. No “suspicious” genes were found in the patients, “the environmental factor therefore had to be investigated,” she continues.
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Today, the investigation into the environmental causes of ALS remains extremely complex, Dr. Lagrange still deplores: "It is a rare disease, which causes people to lose their speech quickly and from which people die very quickly", which makes it difficult questioning patients. In addition, the fact that ALS is not subject to mandatory reporting prevents it from being correctly recorded.
To provide “proof” for its hypothesis, the team intends to continue its research in Savoie. Currently, a study on the gyrometer, on an animal model (mice) is underway, led by Professor Camu and Professor Cédric Raoul, research director at Inserm and director of the Montpellier Neuroscience Institute, who is conducting extensive work on possible therapies for ALS.