Gut microbiota and short-chain fatty acids in idiopathic REM sleep behavior disorder and Parkinson’s disease

Background Idiopathic rapid eye movement sleep behavior disorder (iRBD) is a prodromal stage of Parkinson’s disease (PD). This study aimed to investigate whether gut microbiota and short-chain fatty acids (SCFAs) show consistent alterations in iRBD and PD with RBD patients. Methods We enrolled 29 iRBD, 24 PD with RBD, 17 PD without RBD, and 18 normal controls (NC). Fecal microbiota composition was analyzed via 16S rRNA sequencing, and SCFA concentrations via gas chromatography–mass spectrometry (GC–MS). Clinical symptoms were assessed using motor and non-motor scales, and Spearman correlation analysis was performed to explore interrelationships. Results Microbiota analysis revealed that, compared with NC, Bifidobacterium , Blautia_A , and Azospira_A were significantly enriched, whereas Agathobaculum , Clostridium_Q , Faecalibaculum , Photobacterium , Copromonas , UBA3402 , Acetobacter , and Sutterella were reduced in both iRBD and PD with RBD groups. SCFA analysis showed significantly decreased fecal butyric acid and propionic acid levels in both groups versus NC. Correlation analysis demonstrated that in the iRBD group, Bifidobacterium positively correlated with RBD disease duration; butyric acid negatively correlated with NMSS and RBD-HK; propionic acid negatively correlated with NMSS, RBD-HK, and SCOPA-AUT. In the PD with RBD group, Bifidobacterium negatively correlated with SCOPA-AUT and positively with HAMD-17; butyric acid positively correlated with MDS-UPDRS III. Conclusion iRBD and PD with RBD share similar gut dysbiosis and SCFA abnormalities. Elevated Bifidobacterium and decreased butyric acid and propionic acid are candidate markers for iRBD risk stratification, but correlation does not imply predictive ability. Their value in predicting progression to PD requires validation in longitudinal iRBD cohorts.