Progressive familial intrahepatic cholestasis type 2 (PFIC2), a type of progressive familial intrahepatic cholestasis (PFIC), is a severe, neonatal, hereditary disorder in bile formation that is hepatocellular in origin and not associated with extrahepatic features. Initially, PFIC2 was reported under the name Byler syndrome. The disease is progressive familial intrahepatic cholestasis type 2 (Monarch Disease Ontology identifier MONDO_0011156). Also known as: ABCB11 progressive familial intrahepatic cholestasis, BSEP deficiency, PFIC2, cholestasis, progressive familial intrahepatic 2, cholestasis, progressive familial intrahepatic, type 2, progressive familial intrahepatic cholestasis caused by mutation in ABCB11.