Nineteen (45.2%) out of 42 differential taxa, including butyrate-producing bacteria (e.g., Roseburia, Lachnospiraceae_ND3007_group, Lachnospira, [Eubacterium]_ventriosum_group, Butyricicoccus, Faecalibacterium, and family Lachnospiraceae), hydrogen sulfide-producing Desulfovibrio, mucin-degrading Akkermansia, Collinsella, Oscillospiraceae_UCG-002 and −005, were significantly and similarly altered in RBD and early PD when comparing to the control (unadjusted MaAsLin 2, all q values <0.05, Fig. 3a, Supplementary Dataset 8). This evidence concerns the gene MUC5AC and Parkinson disease.