Changes in gut microbes could be related with an onset of rheumatoid arthritis, eventually translating into symptoms that can be diagnosed, according to a study.

In individuals who developed the autoimmune condition, researchers found that the most number of changes, or "instabilities", in specific strains of gut bacteria (of Prevotellaceae species) were seen 10 months prior to diagnosis -- suggesting that the gut changes could signal a late stage.

An autoimmune disorder is that in which healthy tissues and organs are attacked by the immune system, which normally helps the body fight infection and disease.

Rheumatoid arthritis is a chronic (persistent) autoimmune condition in which there is inflammation, and therefore, pain in one's joints.

However, it was not clear if changes, or "instabilities", in gut bugs trigger the development of the disease or follow it, the researchers from the University of Leeds, UK, said.

The findings, published in the Annals of the Rheumatic Diseases, could help identify those most at risk of rheumatoid arthritis and require personalise treatment, they said.

The team tracked 124 people at risk of developing rheumatoid arthritis for a period of 15 months -- seven were newly diagnosed, 22 were healthy, and the remaining were at risk. Stool and blood samples, taken five times during the study period, helped analyse changes in gut microbes.

The researchers found that those at risk had 'anticyclic citrullinated protein', or anti-CCP, antibodies -- known to attack healthy cells and to be specific to rheumatoid arthritis -- and experienced joint pain in the past three months.

Of the 124 participants, 30 went on to develop the condition, the researchers said.

The team found that diversity of gut microbes in these 30 had notably reduced, compared to the healthy participants. Specifically, 'alpha diversity' -- a common measure of gut health and closely related with disease status -- had reduced.

However, alpha diversity was also reduced in those who did not progress to developing rheumatoid arthritis, the researchers found.

In these participants, the autoimmune condition was related to anti-CCP antibody levels -- those having low levels of the antibodies specific to rheumatoid arthritis had a gut microbe diversity similar to that in the healthy group, the team said.

Risk factors known to contribute to rheumatoid arthritis, such as genetic and blood-related ones, were also linked with a lower diversity of gut bugs.

However, the greatest instability in gut bugs was seen in the participants who developed the chronic condition up to 10 months prior to diagnosis -- following which the gut profile remained relatively stable, the researchers said.

This suggested that changes to the gut microbes could be a late stage phenomenon, they said.

The authors said that being an observational study, direct cause-and-effect links between gut changes and developing rheumatoid arthritis could not be drawn.

"Individuals at risk of rheumatoid arthritis harbour a distinctive gut microbial composition, including but not limited to an overabundance of Prevotellaceae species. This microbial signature is consistent and correlates with traditional risk factors," the authors wrote.

"(Long-term) examination shows a dynamic microbial environment preceding rheumatoid arthritis onset. Further research into this late phase of disease development is merited, especially given the potential of the gut microbiome as a target for prevention, including in high-risk individuals with imminent arthritis," they wrote.

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