The LYNX study is researching a new medicine, sevasemten (known as EDG-5506), for children with Duchenne Muscular Dystrophy (DMD), a muscle-weakening disease. This study is divided into two parts: Part A is a 12-week period where children will randomly receive either the medicine or a placebo (a pill without medicine), and Part B is a 92-week period where all children will receive the medicine. Researchers want to see how safe the medicine is, how it moves through the body (pharmacokinetics), and if it helps reduce muscle damage. Up to 72 children, aged 4-9, will take part, with some groups not using corticosteroids (a type of medicine) joining after safety checks. To join, children must have a specific gene change and perform certain physical tasks. They should not have other serious health conditions or have taken other test medicines recently.

• The study lasts for about 2 years, with regular doctor visits.
• Participants may receive a placebo or the test medicine initially.
• There may be compensation for participation.