NEFL and amyotrophic lateral sclerosis: Cerebrospinal fluid (CSF) and blood NfL levels are increased in the vast majority of neurological conditions with the highest concentrations in individuals with human immunodeficiency virus (HIV)-associated dementia, frontotemporal dementia (FTD), and amyotrophic lateral sclerosis (ALS; Bridel et al., 2019; Ashton et al., 2021).