Gut microbiota composition across clinical subtype and antibody burden in myasthenia gravis.

BACKGROUND: Myasthenia gravis (MG) exhibits clinical heterogeneity ranging from ocular to generalized forms. Although gut microbiota has been implicated in autoimmune diseases, its relationship with clinical subtype and antibody burden in MG remains unclear. METHODS: We conducted a cross-sectional study of fecal microbiota in 14 patients with MG (3 ocular and 11 generalized) and 10 healthy controls using 16S rRNA sequencing. Patients with MG were stratified according to acetylcholine receptor antibody (AChR-Ab) titers into low (n = 5), moderate (n = 5), and high (n = 4) groups. RESULTS: Alpha and beta diversity did not differ significantly between clinical subtypes or antibody-defined groups. Exploratory genus-level analyses identified nominal differences in the relative abundance of several bacterial genera across both clinical subtype and antibody-defined groups. SCFA-associated taxa, including Anaerostipes, Blautia, and Faecalibacterium, appeared relatively more abundant in ocular MG and lower antibody groups, whereas Streptococcus and Bacteroides appeared relatively more abundant in generalized MG and higher antibody groups. PICRUSt2-based analyses were used to explore variation in predicted metabolic pathways between groups; however, no pathway remained significant after correction for multiple testing. CONCLUSIONS: Descriptive genus-level microbiome patterns were observed across both clinical subtype and antibody-defined groups despite similar global diversity measures. These exploratory findings suggest that microbiome variation within MG may be associated with multiple aspects of disease heterogeneity. However, given the small sample size, particularly within the ocular MG subgroup, these observations should be considered hypothesis-generating and require validation in larger independent cohorts.