The bacteria in our gut are known to affect our digestive system, but a new study from the Mayo Clinic found that they also predict our risk of rheumatoid arthritis.

Rheumatoid arthritis is a common inflammatory disorder that causes painful swelling in the joints. The autoimmune disease affects more than 1.5 million Americans.

Scientists have a limited understanding of the processes that trigger the disease, but Veena Taneja, Ph.D., an immunologist at Mayo Clinic's Center for Individualized Medicine, and her team identified intestinal bacteria as a possible cause. Their studies indicate that testing for specific gut microbiota — the microbes living in our gut that include at least 1,000 different species of bacteria — can help physicians predict and prevent the onset of rheumatoid arthritis.

The study, which was published in Genome Medicine, compared rheumatoid arthritis patients and their relatives to a healthy control group. The team's goal was to find a biomarker that predicts susceptibility to rheumatoid arthritis. They noted that an abundance of certain rare bacterial lineages causes a microbial imbalance that is found in rheumatoid arthritis patients.

"Using genomic sequencing technology, we were able to pin down some gut microbes that were normally rare and of low abundance in healthy individuals, but expanded in patients with rheumatoid arthritis," Taneja says.

In the future, intestinal microbiota and metabolic signatures could help scientists build a predictive profile for who is likely to develop rheumatoid arthritis and the course the disease will take, says Taneja.

In a second study, Dr. Taneja treated one group of arthritis-susceptible mice with a bacterium, Prevotella histicola, and compared that to a group that had no treatment. The study found that mice treated with the bacterium had fewer symptoms associated with rheumatoid arthritis.

"These are exciting discoveries that we may be able to use to personalize treatment for patients," Dr. Taneja says.