Expanded Access Protocol for an Intermediate Size Population - RAVICTI for Byler Disease

Inclusion Criteria: * Byler Disease as identified by a homozygous mutation in ATP8B1 predicted to yield a G308V missense mutation * Total serum bile acid \> 100 µM * Male or female subjects of age greater than 130 days to begin screening procedures * Male or female subjects of age greater than 180 days to begin RAVICTI therapy * Ability and willingness to adhere to all study protocols * Access to intermittent phone contact * Written informed consent Exclusion Criteria: * Prior surgical interruption of the enterohepatic circulation (including but not limited to partial biliary diversion and/or ileal exclusion) * Liver transplantation * Other diagnosed concomitant liver disease * Evidence of portal hypertension * Platelet count \< 150,000 and * Spleen palpable \> 2 cm below the costal margin, or * History of a clinical complication/feature c/w portal hypertension * esophageal or gastric varix or variceal hemorrhage * ascites * hepatic encephalopathy * Coagulopathy (PT \> 15 seconds or INR \> 1.5) despite vitamin K therapy * ALT \> 10 X ULN * Allergy/hypersensitivity to RAVICTI or 4-phenylbutyrate * Severe concurrent illnesses, such as neurological, cardiovascular, pulmonary, metabolic, endocrine, and renal disorders, that would interfere with the conduct and results of the study * Known diagnosis of human immunodeficiency virus (HIV) infection * Cancer or history of cancer * Any female who is pregnant or lactating or who is planning to become pregnant with 1 year of enrollment * Any known history of alcohol or substance abuse