The MicroIBioM study: the gut microbiome in inclusion body myositis.

OBJECTIVES: Inclusion body myositis (IBM) is a disorder with features of both inflammation and degeneration yet without effective treatment. Influences of the gut microbiome on degenerative as well as inflammatory disorders and immune treatments are known. We sought to investigate whether the gut microbiome might influence the development or recalcitrance of IBM.

METHODS: We appealed to IBM patients and their unaffected spouses/cohabitants for stool samples and data on clinical symptoms, gathering questionnaire data (modified Gastrointestinal Symptom Rating Scale (mGSRS), IBM Functional Rating Scale (IBMFRS) and Bristol Stool Scale) and stool samples for 16S rRNA V3V4 metagenomic analysis from 21 IBM and 20 control probands. Bioinformatic analyses used QIIME2 and MicrobiomeAnalyst software packages. LEfSe and Random Forest analysis aimed to identify group specific biomarkers. PICRUSt was used to perform pathway analysis.

RESULTS: No overall differences of alpha and beta diversity were found between IBM and control group. No impact of immune treatments was found, but a reduction in alpha diversity was identified comparing older (≥ 72 years) IBM and control probands. Increased abundances of some genera, in particular Bacteroides, were detected in the IBM group. Bacteroides, Clostridium CAG 352, and Eggerthella were identified as IBM biomarkers at genus level. Gastrointestinal symptoms (mGSRS) correlated with disease severity (IBMFRS).

CONCLUSIONS: General differences of gut microbiome seem unlikely to play a role in the genesis of IBM. Whether the late occurring or the more specific differences detected are part of the disease course needs to be addressed by investigations of further biosamples.

PMID: 41562342