Is gut bacteria key for understanding chronic fatigue syndrome?
It was only in the 1980s that chronic fatigue syndrome (CFS) finally received its official title, and since then, it has received a great deal attention.
Characterized by extreme fatigue that cannot be pinned to any underlying pathology, CFS remains a difficult condition to diagnose and treat.
Other symptoms include a loss of cognitive ability, sleep disturbances, enlarged lymph nodes, muscle pain, sore throat, and joint pain.
Also known as myalgic encephalomyelitis (ME) and, more recently, systemic exertion intolerance disease, the causes of CFS are still a mystery.
Some researchers believe that viral infections might be to blame, some point to psychological stressors, and others still think it could be hormonal or an immune system malfunction.
A new study, published in the journal Microbiome, asks whether gut bacteria may have a part to play. This connection might, at first glance, seem obscure. However, up to 90 percent of people with CFS also have irritable bowel syndrome (IBS), which makes a potential relationship easier to imagine.
Relating the microbiome to CFS
Researchers from the Center for Infection and Immunity (CII) at Columbia University's Mailman School of Public Health in New York looked at levels of various gut bacteria in CFS patients both with and without IBS. Their study is one of the first to investigate the microbiome's relationship with CFS and IBS.
The study looked at 50 patients, recruited from four ME clinical sites, and 50 matched healthy controls. They investigated stool samples for bacterial species and took blood samples to assess levels of immune molecules.
When the species of bacteria were analyzed, many of them were shown to be significantly associated with CFS. These were:
Their combined relative abundance was found to predict diagnosis. Other species were also seen in different levels, depending on whether or not IBS was present alongside CFS.
The top biomarkers for CFS with IBS were increased levels of unclassified Alistipes and decreased levels of Faecalibacterium, while the top biomarkers for CFS without IBS were increased levels of unclassified Bacteroides and decreased Bacteroides vulgatus.
The researchers also saw that the severity of participants' symptoms - such as fatigue and pain - correlated with specific bacterial types and certain metabolic pathways.
"Individuals with ME/CFS have a distinct mix of gut bacteria and related metabolic disturbances that may influence the severity of their disease."
Dorottya Nagy-Szakal, co-lead investigator
No significant differences were found in immune markers, although the authors note that this might be because only a few participants had CFS for a short period of time. Previous research suggests that immune changes only appear earlier on in the condition.
Understanding CFS and gut bacteria
"Our analysis suggests that we may be able to subtype patients with ME/CFS by analyzing their fecal microbiome," says Brent L. Williams, co-lead investigator and assistant professor of pathology and cell biology at CII. "Subtyping may provide clues to understanding differences in manifestations of disease."
Although a relationship between gut bacteria and the brain might seem to be a leap, there is growing evidence that there is, in fact, a great deal of communication between the two. Our guts send neuronal and hormonal signals to the brain. At the same time, gut bacteria produce myriad byproducts that have an influence on the gut itself.
Senior author W. Ian Lipkin explains: "Much like IBS, ME/CFS may involve a breakdown in the bidirectional communication between the brain and the gut mediated by bacteria, their metabolites, and the molecules they influence."
The hope is that by probing the relationship between gut flora and CFS, we might gain more insight into a condition that has, so far, evaded our understanding. Lipton continues: "By identifying the specific bacteria involved, we are one step closer to more accurate diagnosis and targeted therapies."