This study aims to test a new medicine called S-606001 for adults with Late-onset Pompe Disease (LOPD). LOPD is a condition caused by a shortage of an enzyme called acid alpha-glucosidase (GAA) which helps break down complex sugars in the body. Participants will continue their usual treatment, known as **Enzyme Replacement Therapy (ERT)**, and add S-606001 to see if it helps.

• The study is for adults over 18 who weigh more than 40 kg (88 lbs) and have been on ERT for at least two years.
• Participants need to be able to walk at least 75 meters in 6 minutes for testing.
• People who are pregnant, have certain medical conditions, or have recently tried other treatments for Pompe disease cannot join.

Participants will be closely monitored to check if the new medicine is safe and effective. The study will measure how the body responds to S-606001 and any effects it has on their health. It is important to discuss with a doctor to understand the benefits and risks before joining.