In the subgroup analysis by gender, feeling things falling when asleep (β = 0.100; P = 0.004) showed a significant association with higher serum NfL levels in PD males (Fig. 3C); and the association for dream nocturnal behavior (β = 0.054; P = 0.032) was still significant in PD females but turned non-significant in PD males (Fig. 3D). The gene discussed is NEFL; the disease is Parkinson disease.