Inclusion Criteria :  Common criteria for retrospective MS patients:  Patients aged 18 years or older Clinical isolated syndrome (CIS) with or without dissemination in space Patients affiliated to an appropriate health insurance  Criteria for Aggressive MS group  • Start of a 2nd line therapy within the two years following the CIS  Criteria for Non aggressive MS group  No conversion according to McDonald criteria from clinical isolated syndrome to multiple sclerosis within 2 years or Conversion based to McDonald criteria treated or not with first line disease modifying therapy within 2 years. Have a minimum of least 2 years of follow-up.  Healthy volunteers  Aged 18 years or older No history of clinically isolated syndrome or MS  Pairing criteria :  Age +/- 5 years Sex  Prospective MS Patients  Patients aged 18 years or older Clinical isolated syndrome (CIS) with or without dissemination in space Patients affiliated to an appropriate health insurance  Exclusion Criteria :  Ongoing participation to a another study Refusal to genetic analyses Immunosuppressive drug at the time of blood collection Adults under a legal protection regime (guardianship, trusteeship, judicial safeguard) Pregnancy