Background

Autoimmune limbic encephalitis (LE) is a condition where the body’s own immune system mistakenly attacks brain cells, causing inflammation and problems with how nerve cells work. A certain inherited genetic change (called *07:01) in a particular immune gene (called HLA-DRB1), is often found in people with the most common type of LE, known as LGI1 autoantibody encephalities. However, this genetic change is also fairly common in people without this condition, so having it alone isn’t enough to cause the disease.
Researchers wondered if there might be a “middle step” — something that works alongside the genetic change to raise the risk of developing LGI1 autoantibody encephalities. They focused on one possible factor: the gut microbiome (the community of bacteria and other microbes living in our digestive system).

Research

The team studied the genetic profile of gut microbes from 42 people with LGI1 autoantibody encephalities and compared it to gut microbes from 27 healthy relatives. Overall, they didn’t see major differences between the two groups. However, they did find small but consistent changes in the types and balance of gut bacteria in patients. These changes became more noticeable in people who had more copies of the HLA-DRB1*07:01 genetic change. The researchers think these gut microbe shifts might encourage inflammation in the brain.

Potential Impact

This is the largest gut microbiome study so far for this rare brain condition. The results are intriguing but larger studies are needed to confirm the findings, ideally with many research groups working together. Since gut microbes might influence brain inflammation, this kind of research could also be useful for understanding epilepsy and other brain disorders in the future.