In the validation cohort, we confirmed higher levels of CSF NFL in MSA (5938 ± 4267 ng/L) compared with PD (1103 ± 442 ng/L; p < 0.001) and controls (1290 ± 664 ng/L; p < 0.001; Table S4 in Supplementary Material). Here, NEFL is linked to Parkinson disease.