Cerebrotendinous xanthomatosis: defective liver mitochondrial hydroxylation of chenodeoxycholic acid precursors.

Oxidation of the side chain of 5 beta-cholestane-3 alpha, 7 alpha-diol, 7 alpha-hydroxy-4-cholesten-3-one, and 5-cholestene-3 beta, 7 alpha-diol has been studied in subcellular fractions of liver from a patient with cerebrotendinous xanthomatosis (CTX) and a control subject. All intermediates were efficiently 26-hydroxylated and further converted to the corresponding 26-carboxylated derivatives by the mitochondrial fraction of normal human liver. No such conversion was observed with the mitochondria from the liver of the CTX patient and the control subject. 12 alpha-Hydroxylation of the patient and the control subject. 12 alpha-Hydroxylation of the substrates was very efficient with the microsomal fractions from both subjects. Bases on these and previous findings (Oftebro, H., I. Björkhem, S. Skrede, A. Schreiner, and J. I. Pedersen. 1980. J. Clin. Invest. 65: 1481-1430), it i concluded that the metabolic defect in CTX is a complete lack of mitochondrial C27-steroid 26-hydroxylase. In CTX the precursors of chenodeoxycholic acid are first attacked by the microsomal 12 alpha-hydroxylase and subsequently by the microsomal 25-hydroxylase as an alternate route to cholic acid formation. This explains the increased ratio of cholic acid to chenodeoxycholic acid observed in the bile of these patients. In the normal liver the formation of both cholic acid and chenodeoxycholic acid involves a mitochondrial 26-hydroxylation.