NEFL and amyotrophic lateral sclerosis: Furthermore, the recognition of NfL as a suitable biomarker to assess treatment efficacy could accelerate the testing of new drugs, as highlighted by approval of tofersen by the US Food and Drug Administration in 2023 for amyotrophic lateral sclerosis associated with a mutation in the SOD1 gene—partly on the basis of the drug’s ability to decrease NfL concentrations.