NEFL and Parkinson disease: We found similar results in the London cohort, where blood levels of NfL correlated with age in the whole cohort (ρ = 0.290, p = 0.001), in controls (ρ = 0.411, p = 0.037), and in patients with PD (ρ = 0.483, p = 0.031), but not in patients with APD.