Roseburia-Associated Gut–Brain Axis Alterations in Relapsing–Remitting Multiple Sclerosis: Evidence from a Household-Matched Case–Control Study

Background/Objectives: Gut microbiota (GM) dysbiosis has been implicated in multiple sclerosis (MS) pathogenesis, influencing inflammation and neurodegeneration, but findings remain inconsistent due to environmental and methodological variability. This study aimed to identify possible microbial biomarkers of MS status and disease severity by profiling gut microbiota and short-chain fatty acid (SCFA) patterns in people with relapsing–remitting MS (pwRRMS), using household-matched healthy controls (HC) to minimize environmental variability. Methods: Twenty-four pwRRMS and their respective household-matched healthy controls (HC) were enrolled, with dietary and lifestyle habits monitored. GM composition was assessed by 16S rRNA gene sequencing, and fecal SCFAs were quantified using gas chromatography–mass spectrometry. PwRRMS were stratified by Expanded Disability Status Scale (EDSS) and Multiple Sclerosis Severity Score (MSSS). Results: β-diversity did not differ between groups. However, α-diversity was significantly reduced in pwRRMS, particularly in those with greater disability. Reduced diversity was associated with lower abundance of butyrate-producing genera (Roseburia, Faecalibacterium, Coprococcus) and enrichment of Oscillibacter and UBA1819, alongside a downward trend in fecal butyrate and propionate levels. Conclusions: RRMS and greater disease severity are associated with gut microbial alterations characterized by reduced SCFA-producing bacteria. Despite limitations including small sample size and sex imbalance, the household-matched design strengthens internal validity. Our findings highlight the potential of targeting the gut microbiota, an accessible compartment within the gut–brain axis, for MS management.