In prodromal PD participants, increased possibilities of daytime sleepiness on three situations (sitting and talking to someone (β = 0.021; P = 0.018), sitting quietly after lunch (β = 0.021; P = 0.004), stopped in traffic in a car (β = 0.028; P = 0.001)) were significantly correlated with a greater rate of the increase in serum NfL levels (Supplementary Table S14). The gene discussed is NEFL; the disease is Parkinson disease.