Determine the Prevalence of Exocrine Pancreatic Insufficiency (EPI) in Pediatric and Adult Participants With Alagille Syndrome After Liver Transplantation

The goal of this clinical trial is to determine the prevalence of exocrine pancreatic insufficiency (EPI) in a population of pediatric and adult participants with Alagille Syndrome (ALGS) post liver transplant. During the study, participants will: * Consume a high fat diet * Keep a diary of their abdominal signs and symptoms, and stool frequency and consistency * Collect stool for laboratory testing

Inclusion Criteria: * Male and female participants ages 7-50 years inclusive. * Confirmed diagnosis of ALGS * Status post OLT due to ALGS complications. * Participants currently managed with pancreatic enzyme products (PEPs) are allowed pending discontinuation of PEPs for 5 days prior to beginning the 72-hour stool collections. Participants must discontinue PEPs for the entire study period until completion. * Agree to adhere to a high fat diet at least 2 days prior to and during the 72-hour stool collections and monitor dietary consumption through the use of a diet diary. * Have a consistent caregiver for the duration of the study if applicable for enrollment of a child. * Capable of giving written informed consent and assent (if age appropriate). Exclusion Criteria: * Surgical disruption of the enterohepatic circulation (e.g., biliary diversion). * Subjects with alternative etiologies of EPI (e.g., chronic panreatitis, pancreatic resection). * Diets high in medium-chain triglyceride (MCT) oil. * Use of bile acids, bile acid uptake inhibitors, lipid-binding resins, synthetic fat substitutes (e.g. Olestra), and diaper rash ointments (note that H2 antagonists and proton pump inhibitors \[PPIs\] are permitted if on a stable and consistent regimen throughout the duration of the study). * History or presence of other concomitant liver diseases such as liver transplant rejection with cholestasis, hepatitis B or C virus infection, HIV, primary sclerosing cholangitis (PSC), alcoholic liver disease, autoimmune hepatitis, metabolic-associated fatty liver disease (MASLD)/non-alcoholic steatohepatitis (NASH) or significant chronic allograft rejection. * Currently pregnant or breastfeeding. * Cancers except for in situ carcinoma or cancers treated at least 5 years prior to screening with no evidence of recurrence. * Participation in a clinical trial and received an investigational product within the last 30 days. * Use of anti-diarrheal, anti-spasmodic, and/or cathartic laxatives. Change in osmotic laxatives within the past 3 months.