This study is about understanding a liver problem in babies called *cholestasis*, where the liver doesn't work properly, causing yellow skin and eyes (jaundice). The study gathers information from babies with this condition to help doctors learn more about it. This includes collecting blood and tissue samples when they are already needed for medical reasons.

The study will follow babies with a condition called biliary atresia very closely until they are 20 years old or have a liver transplant. Other babies with different types of cholestasis are also followed, but if they get better, they have fewer follow-ups. All information is stored safely and used for research.

• The study lasts until the child is 20 years old or until they receive a liver transplant.
• Blood and tissue samples are collected during medical visits, so no extra visits are needed for this.
• Participation helps doctors learn more about liver diseases in babies, which could help future patients.

To join, babies must be younger than 180 days old with specific liver conditions, and parents must agree to participate. Babies with severe liver issues or other specific conditions cannot join.