Pertaining to anatomical extent of motor degeneration, neither CSF nor serum NFL levels differ among patients belonging to the different diagnostic categories of the El Escorial criteria (Feneberg et al., 2018), and serum NFL levels are not influenced by neuroimaging-based disease stages as defined by DTI measures of degeneration of cerebral white matter tracts reflecting the neuropathological staging of ALS (Brettschneider et al., 2013; Verde et al., 2019b). This evidence concerns the gene NEFL and amyotrophic lateral sclerosis.