Background: \- Ryanodine receptor type 1-related myopathies (RYR1-RM) are the most common non-dystrophic muscle diseases that people are born with in the U.S. They affect development, muscles, and walking. Researchers want to test a new drug to help people with these diseases. Objectives: \- To see if the drug N-acetylcysteine decreases muscle damage in people with RYR1-RM. To see if it improves their exercise tolerance. Eligibility: \- People age 7 and older with a confirmed genetic diagnosis of RYR1 or a clinical diagnosis of RYR1 and a family member with a confirmed genetic diagnosis. Design: * Participants will be screened with a checklist of criteria. Adult participants may have a muscle biopsy. A needle will remove a tiny piece of muscle in the lower leg. * Study visits will take several days. * Visit 1: * Medical history * Physical exam * Blood, urine, and saliva tests * Questions about symptoms and quality of life * Heart, lung, and walking tests * Muscle Oxygenation Capacity Test. A blood pressure cuff around the thigh will be tightened for up to 10 minutes. * Biodex testing, stretching the leg against resistance * Muscle ultrasounds. A probe will be moved over the skin. * Participants may be photographed or videotaped during procedures. * They may have a muscle biopsy. * Six months later, visit 2 will repeat visit 1. Participants will start taking the study drug dissolved in water or placebo three times a day for 6 months. * Participants will stay at NIH for 2 days after starting the study drug. * Participants will be contacted by phone during the study to monitor side effects * Six months after starting the study drug, study visit 3 will repeat some or all of visit 1.
Age range
7 Years
Sex
ALL
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AI-rewrites the medical criteria so a patient or caregiver can understand them. Always confirm with the trial site.
Bring these to your next appointment. They're a starting point for a shared conversation — not a sign you qualify or a recommendation to enrol.
Generated to help you prepare — always confirm anything about your own eligibility and care with the study team and your doctor.
The trial coordinator is the person who runs the study day to day. These cover the practical side — logistics, costs, and what taking part would actually mean for your life. The study team confirms whether you meet the criteria; these are questions to ask, not a sign you qualify.
A starting point for the conversation — always confirm anything about your own eligibility, costs, and care with the study team and your doctor.
Urine 15-F2t Isoprostane Concentration
Timeframe: 12 months
Six Minute Walk Test (6MWT)
Timeframe: 12 months