CYP7B1 Background Information P450 enzymes constitute a family of monooxygenase enzymes that are involved in the metabolism of a wide array of endogenous and xenobiotic compounds including cholesterol (1). CYP8B1 moderates the ratio of cholic acid over chenodeoxycholic acid to control the solubility of cholesterol (2). P450 cholesterol 7 -hydroxylase, CYP7A1, is the rate limiting enzyme of bile acid synthesis in the liver, and its expression is mediated by the bile acid receptor FXR (3). CYP27A1 catalyzes vitamin D(3) 25-hydroxylation and is localized to the mitochondria in kidney and liver (4). CYP7B1 (oxysterol 7-alpha-hydroxylase) functions as an enzyme in the alternate bile acid synthesis pathway (5). Specifically, CYP7B1 metabolizes 25- and 27-hydroxycholesterol (5). The gene encoding human CYP7B1 maps to chromosome 8q21.3 (6). Mutations in the CYP7B1 gene may cause a metabolic defect in bile acid synthesis characterized by elevated urinary bile acid excretion, severe cholestasis, cirrhosis and liver synthetic failure (6).
