Your participation in the study will begin once you have completed all required procedures before the treatment phase starts.

This study will compare the effects of AOC 1020 with a placebo (an inactive substance that looks like the study medication but contains no active ingredient). You will be randomly assigned to receive either AOC 1020 or placebo. Neither you nor your doctor will know which treatment you are receiving during the study.

You will receive the assigned treatment through an intravenous infusion (a slow injection directly into your vein).

The study medication AOC 1020 is a specially designed antibody that targets a specific protein and delivers genetic material to help reduce the production of a protein called DUX4, which is involved in facioscapulohumeral muscular dystrophy.

If you are assigned to the placebo group, you will receive 0.9% saline solution (salt water) through the same intravenous infusion method.

The infusions will be administered at regular intervals throughout the study period.

Throughout the study, various assessments will be performed to measure how the treatment affects your condition.

You will undergo a 10-meter walk or run test where your speed will be measured as you walk or run a distance of 10 meters. This test will be performed multiple times during the study.

A Timed-Up-and-Go test will be performed, which measures the time it takes for you to stand up from a chair, walk a short distance, turn around, walk back, and sit down again.

Your muscle strength will be tested using quantitative muscle testing, which measures the strength of different muscle groups in your arms and legs.

You will be asked to complete questionnaires about your upper body function, your ability to perform daily activities, and how fatigue affects you.

You will be asked to rate your pain levels using a numerical scale and provide your overall impression of how severe your condition is and whether it has changed.

Blood samples will be collected to measure specific markers related to the disease, including a protein called creatine kinase and other biological indicators.

At Week 78 (approximately 18 months after starting treatment), a comprehensive evaluation will be performed.

The primary measurement will be the change in your walking speed on the 10-meter walk or run test compared to your speed at the beginning of the study.

Additional measurements at this time point will include the Timed-Up-and-Go test, upper body function questionnaire, and muscle strength testing.

These assessments will help determine the effectiveness of the treatment on your functional mobility and overall condition.

Between the start of treatment and Week 78, you will have multiple visits where the same assessments will be repeated to track changes over time.

Your safety will be monitored continuously throughout the study, and any side effects or changes in your health will be recorded.

The total duration of your participation in the study will extend until approximately April 2028, as this is when the study is expected to be completed.