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

• Fecal Fat (Diagnostic test): coefficient of fat absorption

Primary outcomes

• Dietary fat absorption [At the completion of the 72-hour stool collection period]: Dietary fat absorption is measured by calculating the percent of fat absorption (0-100%). Higher percentage of fat absorption indicates good fat absorption.

Sex: All, ages: 7 Years to 50 Years

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.