We recently developed an ultrasensitive single molecule array (Simoa) immunoassay for NfL, which is by the far the most sensitive platform for detection of NfL, and it provides better agreement between CSF and blood-derived NfL values compared to other analytical platforms.8 We therefore investigated if the levels of NfL in blood are increased in study participants with APD (i.e., PSP, MSA, and CBD) compared with patients with PD and healthy controls in 3 different cohorts including one cohort with early-stage disease. This evidence concerns the gene NEFL and red-green color blindness.