This is an ancillary study using samples collected in the ProBioRIS cohort (NCT06395662). The aim of the project is to highlight new biomarker candidates to assess the risk of conversion to clinically definite multiple sclerosis (CDMS) and disease activity (Evidence of Disease Activity) by taking into account demographic, clinical and MRI parameters. A cohort of healthy subjects will be integrated into the study to serve as a control population. We will study a panel of serum immunoglobulins targeting different Epstein Barr virus antigens to identify latency or reactivation phases. Identifying and prioritizing risk factors for clinical conversion to MS in radiologically isolated syndrome patients is of major importance for the implementation of personalized monitoring and treatment strategies, especially following the recent highlighting of the benefit of background treatments in patients at high risk of CDMS.

Inclusion Criteria:

• RIS patients from the ProBioRIS study with sufficient serum residuals for vitamin D testing and complete EBV serology.
• Healthy subjects who participated in the VDSS trial and who provided consent for the use, for basic research purposes, of human biological samples collected during the trial.

Exclusion Criteria:

• Insufficient sample

Patients with RIS taken from ProBioRIS cohort (NCT06395662) plus healthy controls taken from the VDSS study (NCT05654818).