Congenital bile acid synthesis defect type 2 (BAS defect type 2) is an anomaly of bile acid synthesis (see this term) characterized by severe and rapidly progressive cholestatic liver disease, and malabsorption of fat and fat-soluble vitamins. The disease is Congenital bile acid synthesis defect type 2 (Orphanet_79303). Also known as: Cholestasis, with delta(4)-3-oxosteroid 5-beta-reductase deficiency.