The HSD3B7 gene encodes the 3 beta-hydroxysteroid dehydrogenase type 7 enzyme, a member of the short-chain dehydrogenase/reductase superfamily. This enzyme is located in the membrane of the endoplasmic reticulum and plays a key role in the biosynthesis of bile acids from cholesterol. Specifically, it is responsible for catalyzing the second step in the production of bile acid, the conversion of 7alpha-hydroxycholesterol to 7α-hydroxy-4-cholesten-3-one.
Defects in the HSD3B7 affect its enzyme function and impair the bile acid biosynthesis pathway. This results in Bile Acid Synthesis Defect, Congenital, 1 (CBAS1), a neonatal-onset hepatic disorder characterized by cholestasis, jaundice, hepatomegaly and malabsorption of lipids and lipid-soluble vitamins.