This investigator-initiated research study supported by a pilot grant from MUSC-Siemens research collaboration, aims to test the feasibility and reproducibility of Ultrasound Shear wave elastography as a point of care tool in screening for hepatic fibrosis and steatosis in children 9-17 years of age with Non-Alcoholic Fatty Liver Disease.

This is an Open-label Extension Phase 3 Study to determine whether a study drug called maralixibat is safe and effective in treating itchy skin (pruritus) in children with Progressive Familial Intrahepatic Cholestasis (PFIC). There is currently no treatment approved for PFIC and available medical approaches have limited success.

Open label means both the investigators and the subjects are aware of the drug or treatment being given

A Phase 3 study is large scale trial to confirm and expand information on safety and usefulness of a new drug.

Subjects who participate in this study will receive the study drug. The dose of the study drug will be gradually increased during the study up to a tolerable dose . Subjects will continue to take the medication for about 26 months. Subjects will have approximately 16 study visits over 26 months in this study. Subjects will also be asked questions about health and complete questionnaires at the study visits and as well as at home. A Physical exam and Liver ultrasound will be performed at some study visits. A blood and urine sample will also be collected at some of the study visits.

It is possible that the maralixibat may or may not improve symptoms from PFIC. Even if there is no benefit, other children may benefit from what is learned in this study.