**Study Overview:** This study aims to understand the long-term safety and effectiveness of a drug called *odevixibat* in patients with Alagille syndrome (ALGS). ALGS is a rare genetic disorder that affects various organs, causing symptoms like jaundice (yellow skin), poor growth, and severe itching. **Participation Details:** - The study includes two groups: one who has been part of a previous study and infants under 12 months with ALGS. - Participants will take odevixibat daily during the treatment period (up to 72 weeks) and may continue in an optional extension period if they wish. - Regular clinic visits (every 4 to 16 weeks) are required, and participants will complete questionnaires and have blood and urine tests. **Key Points to Consider:** - **Duration**: Treatment period lasts 12 to 72 weeks, with an optional extension. - **Visits**: Clinic visits are every 4 to 16 weeks. - **Eligibility**: Participants must meet specific health criteria; certain health conditions may exclude participation. This study could help improve treatment for ALGS, but consider the commitment required before joining.