NEFL and X-linked dystonia-parkinsonism: Three males with presymptomatic XDP aged between 40 and 51 years showed low levels of plasma NfL at a median of 5.49 pg/mL versus a median of 15.54 (P < 0.05) and 16.42 pg/mL (P < 0.05) in patients with XDP with dystonia and parkinsonism symptoms at disease onset, respectively (Fig. 3C).