An elevated concentration of NfL in CSF or plasma correlates with disease severity and progression, including in pre-diagnostic ALS (Tortelli et al., 2012; Lu et al., 2015; Gaiani et al., 2017; Gagliardi et al., 2019; Verde et al., 2019; Sugimoto et al., 2020; Bjornevik et al., 2021). This evidence concerns the gene NEFL and amyotrophic lateral sclerosis.