As evidence, the FDA approval of Tofersen, an antisense oligonucleotide for the treatment of SOD1 amyotrophic lateral sclerosis (ALS), on 25 April 2023 is based on changes in blood NfL levels, outlining a major change in the landscape of what biomarkers mean for regulatory approvals. This evidence concerns the gene NEFL and amyotrophic lateral sclerosis.