Biomarker Qualification for Neurofilament Light Chain in Amyotrophic Lateral Sclerosis: Theory and Practice

Objective To explore whether the utility of neurofilament light chain (NfL), as a biomarker to aid amyotrophic lateral sclerosis (ALS) therapy development, would be enhanced by obtaining formal qualification from the US Food and Drug Administration for a defined context‐of‐use. Methods Consensus discussion among academic, industry, and patient advocacy group representatives. Results A wealth of scientific evidence supports the use of NfL as a prognostic, response, and potential safety biomarker in the broad ALS population, and as a risk/susceptibility biomarker among the subset of SOD1 pathogenic variant carriers. Although NfL has not yet been formally qualified for any of these contexts‐of‐use, the US Food and Drug Administration has provided accelerated approval for an SOD1‐lowering antisense oligonucleotide, based partially on the recognition that a reduction in NfL is reasonably likely to predict a clinical benefit. Interpretation The increasing incorporation of NfL into ALS therapy development plans provides evidence that its utility—as a prognostic, response, risk/susceptibility, and/or safety biomarker—is already widely accepted by the community. The willingness of the US Food and Drug Administration to base regulatory decisions on rigorous peer‐reviewed data‐absent formal qualification, leads us to conclude that formal qualification, despite some benefits, is not essential for ongoing and future use of NfL as a tool to aid ALS therapy development. Although the balance of considerations for and against seeking NfL biomarker qualification will undoubtedly vary across different diseases and contexts‐of‐use, the robustness of the published data and careful deliberations of the ALS community may offer valuable insights for other disease communities grappling with the same issues. ANN NEUROL 2024;95:211–216