Study to Evaluate the Efficacy and Safety of Satralizumab in FSHD1

Satralizumab is supplied as prefilled syringe with 1 millimeter of solution for subcutaneous injection corresponding to 120mg of satralizumab. During the first period (double blind period), satralizumab will be administered at weeks 0, 2, 4 and every 4 weeks until week 48. During the second period (open label period), satralizumab will be administered at weeks 48, 50, 52 and every 4 weeks until week 96.

Placebo prefilled syringe is identical in composition to satralizumab, but does not contain the satralizumab active agent. It is identical in appearance and packaging to satralizumab. During the first period (double blind period), placebo will be administered at weeks 0, 2, 4 and every 4 weeks until week 48. During the second period (open label period), satralizumab will be administered at weeks 48, 50, 52 and every 4 weeks until week 96.