In the male subgroup, PD participants who was considered as pRBD (β = 0.011; P = 0.031) (Fig. 5H) and those who displayed two specific RBD behaviors (aggressive or action-packed dreams (β = 0.011; P = 0.033) (Fig. 5I), disturbed sleep (β = 0.010; P = 0.039) (Fig. 5J)) showed an increasing trend of serum NfL levels. This evidence concerns the gene NEFL and Parkinson disease.