Numerous studies have reported decreased blood NfL levels following initiation of MS immunotherapies (Pop and Viuleţ, 1985; Disanto et al., 2017; Novakova et al., 2017; Varhaug et al., 2018; Cantó et al., 2019; Bittner et al., 2020; Calabresi et al., 2021a, b), so that this assay is currently included in most pharmaceutical clinical trials as a secondary measure of treatment effectiveness. This evidence concerns the gene NEFL and myeloid sarcoma.