NEFL and amyotrophic lateral sclerosis: NfL is a novel biomarker, as well as a clinical marker, reflecting disease severity, progression, or therapy response in several neurological disorders such as multiple sclerosis, amyotrophic lateral sclerosis, Huntington’s disease, and Alzheimer’s disease (Disanto et al., 2017; Fyfe, 2019; Gaetani et al., 2019; Kuhle et al., 2019; Olsson et al., 2019; Rodrigues et al., 2020).