A Study to Evaluate the Safety and Tolerability of Maralixibat in Infant Participants With Cholestatic Liver Diseases Including Progressive Familial Intrahepatic Cholestasis (PFIC) and Alagille Syndrome (ALGS).

Inclusion Criteria:

1. Body weight of ≥2.5 kg
2. \<12 months of age at the baseline visit (ROW). \>31 days and \<12 months of age at the baseline visit (US).
3. Gestational age ≥36 weeks at birth. For children born with gestational age between 32 and 36 weeks, a postmenstrual age of ≥36 weeks is required.
4. Diagnosis of PFIC or ALGS

Exclusion criteria:

1. Predicted complete absence of bile salt excretion pump (BSEP) function
2. History of surgical disruption of the enterohepatic circulation
3. History of liver transplant or imminent need for liver transplant
4. Decompensated cirrhosis
5. Presence of any other disease or condition known to interfere with the absorption, distribution, metabolism, or excretion of drugs, including bile salt metabolism in the intestine (e.g., inflammatory bowel disease), per investigator discretion
6. Presence of other significant liver disease or any other conditions or abnormalities which, in the opinion of the investigator or medical monitor, may compromise the safety of the participant or interfere with the participant's participation in or completion of the study