Long-term Safety and Efficacy of Odevixibat in Patients With Alagille Syndrome

Inclusion Criteria: Cohort 1 : 1. Completion of the 24-week Treatment Period of Study A4250-012 2. Signed 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 to remain on the study 3. Caregivers (and age-appropriate patients) must be willing and able to use an electronic diary (eDiary) device as required by the study 4. Sexually active males and females must agree to use a reliable contraceptive method with ≤1% failure rate (such as hormonal contraception, intra-uterine device, or complete abstinence) from signed informed consent through 90 days after last dose of study drug. Cohort 2 : 1. Infant with clinically confirmed ALGS , ≤11 months of age at Study Day 1 2. Body weight ≥2 kg at Study Day 1 3. Gestational age ≥36 weeks. For children born with gestational age between 32 and 36 weeks, a postmenstrual age of ≥36 weeks is required . 4. Signed parent/legal guardian informed consent. Exclusion Criteria: Cohort 1 : 1. Decompensated liver disease, history or presence of clinically significant ascites, variceal hemorrhage, and/or encephalopathy 2. Patients who were not compliant with study drug treatment or procedures in Study A4250-012 3. Any other conditions or abnormalities which, in the opinion of the investigator, may compromise the safety of the patient, or interfere with the patient participating in or completing the study 4. Known hypersensitivity to any components of odevixibat Cohort 2 : 1. Patient with past medical history or ongoing presence of other types of liver disease including, but not limited to, the following: 1. Biliary atresia of any kind 2. Progressive familial intrahepatic cholestasis (PFIC) 3. Benign recurrent intrahepatic cholestasis 2. 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 3. Patient with past medical history or ongoing chronic diarrhea requiring intravenous fluid or nutritional intervention for treatment of the diarrhea and/or its sequelae 4. Patient has a confirmed past diagnosis of infection with human immunodeficiency virus or other present and active, clinically significant chronic infection 5. Recent infection requiring hospitalization or treatment with parenteral anti-infective within 4 weeks of Study Day 1 or completion of oral anti-infective treatment within 2 weeks prior to the Screening Visit 6. Cancer diagnosis (except for basal cell carcinoma) 7. Chronic kidney disease with an impaired renal function and a glomerular filtration rate \<70 mL/min/1.73 m2 8. Patient with surgical history of disruption of the enterohepatic circulation (biliary diversion surgery) within 6 months prior to the Screening Visit 9. Patient has had a liver transplant, or a liver transplant is planned within 6 months of Study Day 1 10. Decompensated liver disease, history or presence of clinically significant ascites, variceal hemorrhage, and/or encephalopathy 11. International normalized ratio (INR) \>1.4 (the patient may be treated with Vitamin K, and if INR is ≤1.4 at resampling the patient may be enrolled) 12. Serum alanine aminotransferase (ALT) \>10 × upper limit of normal (ULN) at Screening 13. Serum ALT \>15 × ULN at any time point during the last 6 months unless an alternate etiology was confirmed for the elevation 14. Total bilirubin \>15 × ULN at Screening 15. Patient suffers from uncontrolled, recalcitrant pruritic condition other than ALGS. Examples include, but not limited to, refractory atopic dermatitis or other primary pruritic skin diseases. 16. Patient exposed to alcohol or substance abuse in utero 17. Bile acid or lipid binding resins and medications that slow gastrointestinal motility 18. Patient has had investigational exposure to a drug, biologic agent, or medical device within 30 days prior to the Screening Visit, or 5 half-lives of the study agent, whichever is longer 19. Any other conditions or abnormalities which, in the opinion of the investigator may compromise the safety of the patient, or interfere with the patient participating in or completing the study