Long Term Safety & Efficacy Study Evaluating The Effect of A4250 in Children With PFIC

Inclusion Criteria Cohort 1:

• Completion of the 24-week Treatment Period of Study A4250-005 or withdrawn from Study A4250-005 due to patient/caregiver judgment of intolerable symptoms after completing at least 12 weeks of treatment
• Signed informed consent and assent as appropriate
• Patients expected to have a consistent caregiver for the duration of the study
• Caregivers (and age appropriate patients) must be willing and able to use an eDiary device as required by the study

Inclusion Criteria Cohort 2:

• A male or female patient of any age, with a clinical diagnosis of PFIC, including episodic forms (i.e., BRIC), and with a body weight ≥5 kg at Visit S-1.
• Patient must have clinical genetic confirmation of PFIC
• Patients with PFIC, excluding BRIC, must have elevated serum bile acid concentration,specifically measured to be ≥100 μmol/L, taken as the average of 2 samples at least 7 days apart (Visits S-1 and S-2) prior to the Screening/Inclusion Visit (Visit 1).
• Patients with PFIC, excluding BRIC, must have history of significant pruritus and a caregiver-reported observed scratching or patient-reported itching (for patients >18 with no caregiver-reported observed scratching) in the eDiary average of ≥2 (on 0 to 4 scale) in the 2 weeks prior to the Screening/Inclusion Visit (Visit 1).
• Patients with episodic forms of PFIC (i.e., BRIC) must have an emerging flare characterized by clinically significant pruritus and elevated serum bile acid levels/cholestasis as judged by the investigator.
• Patient and/or legal guardian must sign informed consent (and assent) as appropriate. Patients who turn 18 years of age (or legal age per country) during the study will be required to re-consent in order to remain in the study.
• Age appropriate patients are expected to have a consistent caregiver for the duration of the study
• Caregivers and age-appropriate patients (≥8 years of age) must be willing and able to use an eDiary device as required by the study

Exclusion Criteria Cohort 1:

• Decompensated liver disease: coagulopathy, history, or presence of clinically significant ascites, variceal hemorrhage, and/or encephalopathy
• Sexually active males and females who are not using a reliable contraceptive method with ≤1% failure rate (such as hormonal contraception, intra-uterine device, or complete abstinence) throughout the duration of the study and 90 days thereafter
• Patients not compliant with treatment in study A4250-005
• Any other conditions or abnormalities which, in the opinion of the investigator or Medical Monitor, may compromise the safety of the patient, or interfere with the patient participating in or completing the study

Exclusion Criteria Cohort 2:

• Known pathologic variations of the ABCB11 gene that have been demonstrated to result in complete absence of the BSEP protein
• Patient with past medical history or ongoing presence of other types of liver disease including, but not limited to, the following:
• Biliary atresia of any kind
• Suspected or proven liver cancer or metastasis to the liver on imaging studies
• Histopathology on liver biopsy is suggestive of alternate non-PFIC related etiology of cholestasis Note: Patients with clinically significant portal hypertension are allowed.
• Patient with a past medical history or ongoing presence of any other disease or condition known to interfere with the absorption, distribution, metabolism (specifically bile acid metabolism), or excretion of drugs in the intestine, including but not limited to,inflammatory bowel disease.
• Patient with past medical history or ongoing chronic (i.e., >3 months) diarrhea requiring intravenous fluid or nutritional intervention for treatment of the diarrhea and/or its sequelae.
• Patient has a confirmed past diagnosis of infection with human immunodeficiency virus or other present and active, clinically significant, acute, or chronic infection, or past medical history of any major episode of infection req