NfL diffuses quickly due to lower molecular weight and phosphorylation status, with consequent rapid degradation, whereas NfH degrades slowly.8 In addition, NfH is mostly located in large, myelinated axons and is more likely to be released during the later stages of MS.17 NfH, therefore, becomes the predominant axonal protein in CSF in progressive MS, while NfL marks early axonal injury. This evidence concerns the gene NEFL and myeloid sarcoma.