Studies of the mechanism of the increased biosynthesis of cholestanol in cerebrotendinous xanthomatosis. The activity of delta 5-3 beta-hydroxysteroid dehydrogenase

It was recently proposed that the increased biosynthesis of cholestanol in cerebrotendinous xanthomatosis (CTX) is due to increased activity of the delta 5-3 beta-hydroxysteroid dehydrogenase involved in bile acid biosynthesis, causing increased conversion of cholesterol into cholestanol through 4-cholesten-3-one. Our attempts to confirm this hypothesis have failed. Liver biopsy specimens from two patients with CTX did not have any increased capacity to catalyze conversion of 7 alpha-hydroxycholesterol into 7 alpha-hydroxy-4-cholesten-3-one. Further, we did not find any changes in the activity of liver microsomal delta 5-3 beta-hydroxysteroid dehydrogenase after feeding rabbits with cholestanol or cholesterol. The findings are discussed in relation to our hypothesis that the accelerated biosynthesis of cholestanol in CTX is due to an increased conversion of early bile acid intermediates into cholestanol.