Leveraging the salivary microbiome profile to stratify REM sleep behavior disorder and synucleinopathies

Few studies have explored noninvasive biomarkers of synucleinopathies, including Parkinson’s disease (PD), and rapid-eye-movement behavior disorder (RBD), a prodromal stage for these conditions. Human oral/salivary microbiomes are altered in PD, highlighting their potential role in both PD pathogenesis and diagnosis. We analyzed 249 salivary microbiomes of controls and patients with idiopathic RBD and various synucleinopathies, including two subgroups divided based on the presence of RBD symptoms, through both cross-sectional and longitudinal studies. The microbiome composition was strikingly similar between patients with RBD and early PD exhibiting RBD symptoms. The area under the curve range for distinguishing RBD from controls and each synucleinopathy was 0.85–0.94. We further performed pseudotime trajectory analysis of the microbiome compositional space; populations with low diversity, enriched Streptococcus , and depleted Neisseria exhibited a brief pseudotime transition from RBD to early PD. Our findings suggest that early PD-like salivary dysbiosis manifests during RBD, allowing for the stratification of synucleinopathies through the innovative use of salivary microbiome profiles.