NEFL and amyotrophic lateral sclerosis: Neurofilament light chain (NfL) is one of the most promising fluid biomarkers but is a nonspecific marker for AD neuronal injury, being increased in AD and non‐AD diseases, such as frontotemporal dementia, amyotrophic lateral sclerosis, and atypical Parkinson's disorder,9 and it does not provide any information about the brain regions damaged.