NEFL and amyotrophic lateral sclerosis: In both diseases, elevated NfL inversely correlated to survival time, suggesting that NfL may be a relevant prognostic biomarker.77 NfL has also been studied in amyotrophic lateral sclerosis serum, correlating to disease progression and decreased survival time, but not disease severity.78 Blood and CSF NfL is amongst the earliest markers to change in patients transitioning from presymptomatic to symptomatic.79 Furthermore, NfL could be used to differentiate amyotrophic lateral sclerosis subtypes.