A sugar molecule churned out by gut bacteria may be one of the missing triggers behind ALS, and eliminating it in mice reversed the disease’s hallmark symptoms. That is the central finding of a study published in Cell Reports (DOI: 10.1016/j.celrep.2025.116906) in early 2025 by a team at Case Western Reserve University, led by neuroscientist Aaron Burberry. The researchers traced a direct inflammatory chain from bacterial glycogen in the intestines, through frontline immune cells, and into the brain, offering the most specific gut-to-neuron mechanism yet described for the most common genetic form of ALS.
Amyotrophic lateral sclerosis destroys motor neurons, progressively stripping people of the ability to move, speak, swallow, and eventually breathe. Roughly 30,000 Americans are living with the disease at any given time, and most survive only two to five years after diagnosis. About 40 percent of inherited ALS cases and up to 10 percent of sporadic ones involve a repeat expansion in a gene called C9orf72. But a long-standing mystery has haunted that statistic: not everyone who carries the mutation gets sick. Something else has to pull the trigger. As of June 2025, this study offers one of the strongest candidates yet.
A sugar the immune system cannot ignore
Glycogen is a branched sugar polymer that many bacteria produce as an energy reserve. In a healthy person, immune cells called myeloid cells encounter microbial glycogen constantly and shrug it off. The C9orf72 gene, Burberry’s group has shown, is a key reason they can. It acts as a brake on an innate immune alarm system known as the STING pathway. When the gene carries its characteristic repeat expansion, that brake weakens. Glycogen that would normally pass without incident instead trips STING into action, launching waves of inflammatory signaling that ripple from the gut into the bloodstream and, ultimately, into the central nervous system.
The mechanistic groundwork was laid in two earlier papers from the same research line. A 2020 study in Nature demonstrated that C9orf72 suppresses STING-driven inflammation in myeloid cells, establishing the gene’s role as an immune gatekeeper. A companion paper showed that gut microbiota could drive systemic and neural inflammation in C9orf72-mutant mice, and that reshaping the microbial community reduced those inflammatory signatures. What the new Cell Reports paper adds is precision: it narrows the culprit from the entire microbiome down to a single class of molecule.
To make that case, the team used metatranscriptomic sequencing of gut bacteria and found that genes responsible for glycogen biosynthesis were abnormally active under disease-relevant conditions. They then turned to gnotobiotic experiments, colonizing germ-free mice with defined bacterial communities, the gold standard for isolating a specific microbial effect. When the bacterial communities produced glycogen, inflammation surged and motor function declined. When the glycogen source was removed, or when C9orf72 function was restored specifically in myeloid cells, inflammation dropped and motor symptoms improved.
The human signal and its limits
The mouse work is mechanistically clean, but the human data is what makes the finding urgent. According to a press release from Case Western Reserve University, roughly 70 percent of the 23 ALS and frontotemporal dementia patients tested in the study carried dangerously elevated glycogen levels. The same press release noted that about one-third of people without the disease showed comparably high levels. These figures come from the university’s summary of the Cell Reports paper rather than from the paper’s abstract directly, so readers should treat the precise percentages with appropriate caution until the underlying patient-level data can be independently reviewed.
“We found that a specific sugar made by gut bacteria can trigger the inflammatory cascade that damages motor neurons in people with C9orf72 mutations,” Burberry said in the Case Western Reserve press release. “This gives us a concrete, targetable mechanism rather than a vague association with the microbiome.”
That gap between 70 percent and one-third is suggestive. If it holds up in larger populations, glycogen burden could help explain why some C9orf72 mutation carriers live full lives while others develop devastating neurodegeneration. It would also shift ALS risk assessment from a purely genetic question to a combined genetic and microbial profile, one that might be more predictive and, crucially, more actionable.
Independent research has already pointed toward the gut as a player in ALS. A 2020 Nature study by Blacher and colleagues found that specific microbial communities, including those associated with the bacterium Akkermansia muciniphila, could modulate motor symptoms in ALS mouse models, partly through metabolites like nicotinamide. Together with the new glycogen findings, these studies reinforce a picture in which the intestinal ecosystem does not merely accompany neurodegeneration but, in certain genetic contexts, actively drives or dampens it.
What the study cannot yet tell us
Twenty-three patients is a small cohort. A sample that size can spotlight a pattern worth chasing, but it cannot establish clinical thresholds, account for variation in diet and geography, or rule out confounders. The raw human metagenomic and metabolite datasets have not been publicly linked in the primary study summaries, which limits independent verification of how glycogen was measured and what cutoff defined “dangerous.”
No one has yet measured glycogen directly in the cerebrospinal fluid or spinal cord tissue of ALS patients. The inflammatory chain described in the paper moves from gut to blood to brain, but the intermediate steps in human tissue are inferred from the mouse models rather than observed in patient samples. Long-term survival data and detailed behavioral scoring from the mouse reversal experiments have also not appeared in the published record, making it hard to judge how durable the improvements were or whether they extended lifespan.
Then there is the one-third of healthy people who also showed elevated glycogen. If high glycogen alone were enough to cause disease, those individuals should be sick. Other protective factors, whether genetic, immune, or dietary, almost certainly modulate the risk, and the current data cannot identify them. The study establishes a plausible mechanism and a striking correlation, but definitive causal proof in humans will require larger longitudinal cohorts that track glycogen levels before symptoms appear and follow participants over years.
How bacterial glycogen interacts with the protective species and metabolites identified in earlier microbiome-ALS research is also unresolved. The field now has multiple threads pointing to the gut’s influence on neuroinflammation, but they have not been woven into a single predictive model that can explain who gets sick, when, and how quickly the disease progresses.
From mechanism to medicine
Clinical translation could take several forms: drugs that inhibit bacterial glycogen synthesis, dietary interventions that shift gut flora away from high-glycogen producers, or therapies that restore STING regulation in myeloid cells. None of these approaches has entered human trials for ALS as of May 2025. Any future treatment based on this pathway would need to demonstrate that lowering glycogen or calming STING activity slows functional decline in people, not just in mice. Safety will be a central concern, because glycogen metabolism and innate immune signaling are fundamental biological processes. Bluntly suppressing either one could leave patients vulnerable to infections or other complications.
One nearer-term possibility is screening. If bacterial glycogen biosynthesis genes can be reliably detected through stool-based metatranscriptomics, clinicians could eventually test C9orf72 mutation carriers for elevated glycogen before any symptoms appear. That would open the door to closer monitoring or early enrollment in prevention trials targeting the microbiome, a shift from reactive treatment to proactive risk management.
Why this reframes ALS as more than a brain disease
The most consequential implication of this work may be conceptual. For decades, ALS research has focused overwhelmingly on what goes wrong inside motor neurons. The Burberry lab’s findings argue that, at least for C9orf72-linked forms, the disease is systemic: the gut, the immune system, and the nervous system are locked in a feedback loop, and the gut may be where the loop starts. A single microbial product, interacting with a single genetic vulnerability, appears capable of tipping the balance toward neurodegeneration.
As larger human studies come online, the key questions will sharpen. How often is this glycogen-STING pathway active across different ALS subtypes? How early does it switch on? And can modifying it meaningfully change the trajectory for patients who, right now, have almost no options that alter the course of their disease?
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*This article was researched with the help of AI, with human editors creating the final content.
