High-throughput Omic Technology for Identification of Biomarkers of Relapsing Acute Disseminated Encephalomyelitis in Immune Cell Network

Inclusion criteria: Prospective recruitment Pre-inclusion criteria * Age at inclusion between 1 and 18 years (included) * First demyelinating event at inclusion, such as ADEM encephalitis, optic neuritis (NORB) or myelitis, or a combination of these conditions. * Informed consent signed by patient's legal representative * Patient affiliated to or benefiting from a social security scheme Inclusion criteria (confirmation of inclusion and follow-up in one of 3 groups) * MOGAD/ADEM group: presence of serum anti-MOG antibodies and diagnosis of ADEM (according to the International Pediatric Multiple Sclerosis Society Group (IPMSSG) criteria revised in 2013) at the first demyelinating attack. * Non-MOGAD/ADEM group: anti-MOG antibodies negative and diagnosis of ADEM at first demyelinating attack. * MOGAD/non-ADEM group: presence of serum anti-MOG antibodies and diagnosis of myelitis and/or NORB at first demyelinating attack. Retrospective recruitment General inclusion criteria * Age at inclusion between 1 and 18 years (inclusive) * Inclusion (signed consent of the patient's legal representative) in the biocollection from which the samples were taken at the latest at the time of management of a first demyelinating event of the ADEM encephalitis, optic neuritis (NORB) or myelitis type, or a combination of these disorders. * PBMC collected at the time of the first demyelinating event before any immunomodulatory treatment, cryopreserved and available in the biocollection. * Depending on the date of inclusion (if inclusion beyond 6 to 24 months after the first demyelinating event), samples taken at 6 months and then 24 months after the first demyelinating event available in the biocollection for the analyses planned in the study. * Informed consent signed by patient's legal representative * Patient affiliated to or benefiting from a social security scheme Inclusion criteria specific to the 3 study groups * MOGAD/ADEM group: presence of serum anti-MOG antibodies and diagnosis of ADEM (according to the International Pediatric Multiple Sclerosis Society Group (IPMSSG) criteria revised in 2013) at the first demyelinating attack. * Non-MOGAD/ADEM group: anti-MOG antibodies negative and diagnosis of ADEM at first demyelinating attack. * MOGAD/non-ADEM group: presence of serum anti-MOG antibodies and diagnosis of myelitis and/or NORB at first demyelinating attack. Non-inclusion criteria (prospective or retrospective recruitment): * Immunosuppressive therapy in the 6 months prior to treatment for a first demyelinating event. * Systemic corticosteroid therapy or immunomodulating doses of IV polyvalent immunoglobulin or plasma exchange within 3 months prior to treatment for a first demyelinating event. * Brain MRI not performed at diagnosis of first demyelinating event * Poor understanding of the French language