**Study Overview:** This study is checking how safe and effective a medicine called **CRYSVITA®** is for patients in South Korea. **CRYSVITA®** is given as an injection, which means the medicine is delivered through a needle. The study will observe patients who are already using this medicine as their doctor recommended. **Eligibility:** - To join, patients must already be using **CRYSVITA®** and have agreed in writing to be part of the study. If the patient is a child, their legal guardian must also agree and explain the study to them. - Patients who can't use **CRYSVITA®** safely or want to use it for reasons not recommended won't be included. **Key Points:** - The study focuses on people already using **CRYSVITA®**, not new patients. - The goal is to see if the medicine works well and doesn't cause harm in a real-world setting. - Participation involves agreeing to be observed and providing feedback on your experience with the medicine. This study is important to ensure **CRYSVITA®** is safe and helpful for those who need it.