Congenital bile acid synthesis defect type 1 (BAS defect type 1) is the most common anomaly of bile acid synthesis (see this term) characterized by variable manifestations of progressive cholestatic liver disease, and fat malaborption. The disease is Orphanet_79301 (Congenital bile acid synthesis defect type 1). Also known as: 3-beta-hydroxy-delta-5-C27-steroid oxidoreductase deficiency.