Depression: gut microbiota the key to diagnosis?

The gut microbiota is populated by various microorganisms which synthesize compounds called metabolites that are essential for the proper functioning of the human body. Over the last decade, researchers have established links between microbiota imbalances and various diseases, including major depressive disorder (MDD), a psychiatric disorder with significant social consequences. A recent study has confirmed this link and has gone one step further by using the gut microbiota as a diagnostic tool.

A more precise map of the microbiota

Lacking easily measurable biomarkers and based solely on patient interviews, MDD diagnosis is often incorrect or incomplete. In order to get an accurate picture of the gut microbiota in depression, the researchers studied bacteria, viruses, and their metabolites in the stool of a hundred MDD patients and a hundred healthy controls. They identified 3 bacteriophages (viruses that infect bacteria), 47 bacterial species and 50 fecal metabolites that showed notable differences in abundance between MDD patients and healthy controls. According to the researchers, these biomarkers may serve as a complementary tool in the diagnosis of depression, alongside clinical interviews. The analysis of a second cohort showed that these biomarkers made it possible to identify the MDD patients in both cohorts with an accuracy of more than 90%.

Gut-brain axis at the heart of depression?

This mapping also revealed that GABA (a neurotransmitter which decreases brain activity) was found in lower quantities in the stool of MDD patients. According to the researchers, this decrease may be modulated by the altered bacterial composition of MDD patients’ microbiota and may be involved in the development of MDD. The authors speculate that the decrease in gut GABA levels in MDD patients may be correlated with the dysregulation of GABA function in the brain. This hypothesis would seem to confirm the role of the gut-brain axis in major depressive disorder. The study therefore provides new hope for the diagnosis of MDD.