Led by scientists at the University of Chicago, the researchers used advanced genomic analysis techniques to compare stool samples from 122 people who had at least one CA as seen on brain scans, with those from age- and sex-matched, control non-CA participants, including samples collected through the American Gut Project. Initially, they found that on average the CA patients had more gram-negative bacteria whereas the controls had more gram-positive bacteria, and that the relative abundance of three gut bacterial species distinguished CA patients from controls regardless of a person's sex, geographic location, or genetic predisposition to the disease. Moreover, gut bacteria from the CA patients appeared to produce more lipopolysaccharide molecules which have been shown to drive CA formation in mice. According to the authors, these results provided the first demonstration in humans of a "permissive microbiome" associated with the formation of neurovascular lesions in the brain.

Further analysis showed that some gut bacteria compositions could identify aggressive vs non-aggressive forms of the disease as well as those with recent symptomatic hemorrhages. Also, for the first time, they showed how combining gut bacteria data with results from blood plasma tests might help doctors better diagnose the severity of a brain disorder. The results, published in Nature Communications, support a growing body of evidence for the role of gut bacteria in brain health.