<h4>Background</h4>Idiopathic REM sleep behavior disorder (iRBD) indicates an early α-synucleinopathy, offering a window for early detection and intervention.<h4>Objective</h4>Explore a serum-based biomarker panel, comprising NfL, GFAP, t-tau, and UCH-L1, in patients with iRBD, and compare to individuals with synucleinopathy and healthy controls.<h4>Method</h4>This is a cross-sectional, observational study. Here, UCHL1 is linked to synucleinopathy.