The story in detail
Could depression accompanied by REM sleep behaviour disorder represent a distinct biological subgroup? Researchers compared 420 people across four groups, including healthy controls, depression alone, the sleep disorder alone and both conditions together. Stool sequencing showed that the combined group differed from depression alone and resembled the sleep-disorder group in several microbial and metabolic features.
A classification model was also assessed in a separate small dataset. Partial separation of groups does not establish a stool test that predicts future Parkinson’s disease. Diet, medication and other characteristics can influence the microbiome. The study cannot prove causation or justify probiotic treatment. It provides a rationale for longer follow-up that considers sleep features alongside psychiatric symptoms.
Study date: 2026-07-23 · Story: 20 October 2026
What was found?
A comparison involving 420 people found different gut microbial profiles in depression accompanied by REM sleep behavior disorder than in depression alone. The combined group’s profile more closely resembled that of people with the sleep disorder without psychiatric disease.
What does it mean?
The findings may help researchers explore biological subgroups of depression and the gut–brain relationship.
Limitations
Single-time-point sampling cannot establish causation. A microbial profile does not prove that Parkinson’s disease will develop. Diet, medicines and other factors may influence results. The findings do not justify routine testing or probiotic treatment.
Sources and review scope
Original article (DOI) · Reviewed source 1
Original full text, methods and limitations reviewed.
Sources last checked: 20 October 2026.
Editorial expansion: 21.10.2026
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