We found PD participants who had higher RBDSQ scores (β = 0.002; P = 0.011) (Fig. 4 and Supplementary Table S7) and those who were considered as pRBD (β = 0.012; P = 0.009) (Fig. 5A) showed an increasing trend of serum NfL levels. Here, NEFL is linked to Parkinson disease.