Plasma levels of neurofilament light (NfL) differed significantly between groups with post hoc pairwise comparisons indicating higher levels in participants with MSA and 4R-tauopathies (HC vs MSA, p < 0.001; HC vs 4R-tauopathies, p < 0.001; HC vs PD, p = 0.33; PD vs MSA, p = 0.064; PD vs 4R-tauopathies, p = 0.020; MSA vs 4R-tauopathies, p = 1.0). Here, NEFL is linked to Parkinson disease.