Indeed, high levels of NF-L were consistently found in the CSF of patients with multiple sclerosis (MS),2 suggesting that NF-L could be used as a biomarker of MS disease activity (including subclinical activity) and of the response to various MS treatments.2-6 Moreover, high serum NF-L levels in early MS were shown to predict a future increase in MS lesions and brain atrophy.3,5. This evidence concerns the gene NEFL and myeloid sarcoma.