This study is testing a medicine called satralizumab for kids with a muscle condition known as Duchenne Muscular Dystrophy (DMD). DMD is a disease that makes muscles weak over time. Satralizumab is a type of medicine called a monoclonal antibody, which is like a special protein that helps the body's immune system fight certain conditions. The study will check how well this medicine works and if it is safe. It will also look at how the body processes the medicine (pharmacokinetics) and how the medicine affects the body (pharmacodynamics).

Kids aged 8 to 18 who can walk or use a wheelchair can join. They will get the medicine through a shot under the skin every 4 weeks. The study will last several months, and kids will need to visit the clinic for check-ups.

• Participants must take daily oral corticosteroids and cannot have had major surgery recently.
• Kids must be free from severe illnesses like tuberculosis or hepatitis.
• Participants will be in two groups, based on their ability to walk and history of bone fractures.