This clinical trial is focused on studying the long-term safety and effectiveness of a medication called odevixibat (also known by its code name A4250) in patients with Alagille syndrome. Alagille syndrome is a genetic disorder that can affect the liver, heart, and other parts of the body, often leading to symptoms like severe itching. The purpose of this study is to see how well odevixibat works over an extended period and to ensure it is safe for patients to use.

The study involves two groups of patients. The first group includes patients who have already completed a previous study with odevixibat and will continue to take the medication to see if it helps with itching. The second group consists of younger patients, under 12 months old, who will be monitored to evaluate the safety and how well they tolerate the medication. Participants will take odevixibat in capsule form by mouth, and the study will last up to 72 weeks.

Throughout the study, researchers will observe changes in symptoms such as itching and scratching, as well as other factors like sleep quality and overall quality of life. The study aims to provide valuable information on how odevixibat can help manage symptoms of Alagille syndrome over a long period, contributing to better treatment options for those affected by this condition.