In neurodegenerative diseases, such as Alzheimer disease, Parkinson disease, multiple sclerosis, and amyotrophic lateral sclerosis (ALS), NfL has been measured as a readout of neuronal damage.23, 24, 25, 26, 27, 28 Indeed, it is routinely used to measure and track recovery from traumatic brain injury.29 Here, NEFL is linked to neurodegenerative disease.