Genetically confirmed FSHD2: pathogenic mutation in SMCHD1 gene and at least one D4Z4 4qA allele;
Age 18-75 years
Symptomatic limb weakness
Clinical severity score of 2 to 5 (RICCI score; range 0-5), inclusive, at screening:
* Group ambulant patient with a RICCI score of 2 to 4
* Group non-ambulant patient with a RICCI score of 5
Patient giving written consent after written and oral information
Patient affiliated to a social security system
If taking over the counter supplements, willing to remain consistent with supplement regimen throughout the course of the study
Patients with comorbidity not related to the disease that can modify the natural evolution of the disease or would interfere with safe testing in the opinion of the Investigator
Regular use of available muscle anabolic/catabolic agents such as corticosteroids, oral testosterone or derivatives, or oral beta agonists
Contraindication to muscle MRI as per clinic standard practice
Patients who has been to a tropical or subtropical country during the last 3 months
Patients who has practiced physical exercise within 10 hours before blood test
Patients declaring not to be fasting for at least 10 hours
Patients following a particular diet for medical reasons and after prescription by a doctor or dietitian
Patients who regularly consumes large quantities of alcohol
Patients having consumed an illicit recreational drug during the last 3 months
Patients having been vaccinated during the last 3 months
Patients having received a blood transfusion or immunoglobulins during the last 3 months
Patients declaring to be seropositive for HIV, HBV or HCV
Patients having had an infectious episode during the 3 weeks preceding the visit
Use of an experimental drug in an FSHD clinical trial within the past 30 days
Participation in others clinical trials
Pregnant women, breastfeeding women, women of childbearing age without contraception Pregnancy
Patient with legal protection measures (future protection mandate, family empowerment, guardianship, curators) under Article L. 1122-2 of the French Public Health Code
Patient refusing to participate in the study or expressing opposition to participation
