An Extension Study of Maralixibat in Patients With Progressive Familial Intrahepatic Cholestasis (PFIC)

Key Inclusion Criteria: 1. Provide informed consent and assent (as applicable) per Institutional Review Board/Ethics Committee (IRB/EC) 2. Completion of study MRX-502 Exclusion Criteria: 1. Any female who is pregnant or lactating or who is planning to become pregnant 2. Administration of prohibited medication between the MRX-502 EOT visit and the MRX 503 Baseline Visit (Day 0) 3. History of non-compliance in study MRX-502, non-adherence to medical regimens, unreliability, mental instability or incompetence that could compromise the validity of informed consent or lead to non-adherence with the study protocol based on Investigator judgment 4. Experienced an adverse event (AE) or serious adverse event (SAE) related to maralixibat during the MRX-502 study that led to permanent discontinuation of the subject from maralixibat 5. Any other conditions or laboratory abnormalities that, in the opinion of the Investigator or Sponsor Medical Monitor, may compromise the safety of the subject, or interfere with the subject participating in or completing the study 6. Cognitive impairment of the subject or caregiver that would, in the opinion of the investigator, preclude appropriate understanding of study information and compliance with study procedures