MRX-800: A Long-Term Safety Study of Maralixibat in the Treatment of Cholestatic Liver Disease in Subjects Who Previously Participated in a Maralixibat Study

Inclusion Criteria Subjects will need to meet all criteria below to be considered eligible for the study. 1. Provide informed consent and assent (as applicable) per the Institutional Review Board/Ethics Committee (IRB/EC). 2. Previously participated in a maralixibat study and with approval of the Medical Monitor. Previous participation is defined as: * Having completed the EOT Visit, for subjects coming from the maralixibat Phase 2 studies. * Having completed the entire duration of the study (i.e., core and extension, if applicable), for subjects coming from the maralixibat Phase 3 studies. 3. At least 1 year of age 4. Males, and females of non-childbearing potential. Males and non-pregnant, non-lactating females of childbearing potential who are sexually active must agree to use acceptable contraception during the study and 30 days following the last dose of the study medication. Females of childbearing potential must have a negative pregnancy test. 5. Caregivers (and/or age appropriate subjects) must have access to email or phone for scheduled remote visits if applicable. 6. Subject and caregiver willingness to comply with all study visits and requirements. Exclusion Criteria A subject will be excluded from the study if any of the following exclusion criteria are met: 1. Experienced an AE or SAE related to maralixibat during the lead-in protocol that led to permanent discontinuation of the subject from maralixibat. 2. Any conditions or abnormalities (including laboratory abnormalities) which, in the opinion of the Investigator or Medical Monitor may compromise the safety of the subject or interfere with the subject participating in or completing the study. 3. History of non-adherence to medical regimens, unreliability, medical condition, mental instability or cognitive impairment that, in the opinion of the Investigator or Sponsor medical monitor, could compromise the validity of informed consent, compromise the safety of the subject, or lead to non-adherence with the study protocol or inability to conduct the study procedures.