Deconfounded, quantitative microbiome profiling identifies robust multiple sclerosis markers and clinical covariate associations.

Despite a wealth of gut microbiota studies in multiple sclerosis (MS), consistent results are lacking. Here, we study confounder effects and use of quantitative microbiome profiling (QMP) in 228 MS patients (103 untreated) and 2860 population controls (Flemish Gut Flora Project (FGFP)). Total bacterial load was lower in relapsing remitting (RR)MS, while strong fecal moisture effects, indicative of longer transit times, in MS vs. FGFP, were driven by primary progressive (PP)MS. Applying cell count and moisture in deconfounded QMP, we identified 21 differentially abundant genera in MS, with a.o. Lachnobacterium, Blautia enriched, and Clostridium, Bacteroides depleted. Deconfounded QMP across 10 published studies (1065 patients, 874 controls) did not confirm commonly detected markers (Akkermansia, Roseburia), yet lowered Bacteroides, and higher Blautia and Methanobrevibacter emerged as robust MS biomarkers. Lowered butyrate producers (Butyricicoccus, Butyricimonas) merit further investigation. Enterotype stratification linked the low cell count Bacteroides 2 enterotype to low-efficacy DMTs, and the Prevotella enterotype to lower disease severity. Serum glial fibrillary acidic protein (GFAP), a disease progression biomarker, was identified as a covariate of gut microbial variation and inversely correlated with Faecalibacterium and Roseburia abundance in PPMS. Overall, our study provides robust disease markers and emphasizes the importance of QMP and confounder control.