Serum Neurofilament-light Chain and GFAP Levels in Patients From the OFSEP Cohort at Different Landmarks of Multiple Sclerosis

Inclusion Criteria: * The patient has been correctly informed. * The patient must have given their informed and signed consent. * The patient must be insured or beneficiary of a health insurance plan. * The patient is at least (≥)15 years old. * The patient has MS according to diagnosis criteria (Thompson et al. 2017) and: * Participates to the OFSEP-HD cohort (ancillary study); * Has a Expanded Disability Status Scale score comprised between 0 - 7.0; * With or without Disease Modifying Drug; * For Work Package 3: patients enrolled in any OFSEP-HD centre that meet landmark criteria for an active MS (relapse, or Expanded Disability Status Scale progression, or active MRI) during follow-up; * For Work Package 4: patients with a stable disease enrolled in OFSEP-HD study in Nîmes or Nantes University Hospitals. Exclusion Criteria: * Within the past three months, the patient has participated in another interventional study that may interfere with the results or conclusions of this study. * The patient is in an exclusion period determined by a previous study. * The patient is under judicial protection. * The patient refuses to sign the consent. * It is impossible to correctly inform the patient (inability to understand the study, language problem). * The patient is pregnant or breast-feeding. * The patient is under 15 years old. * Inability to answer questionnaires. * Clinically isolated syndrome (CIS) that does not meet the criteria of MS. * Radiologically isolated syndrome (RIS). * Patient with Neuromyelitis optica spectrum disorder.