Genes involved in initial steps of bile acid synthesis

The mechanism and regulation of the degradation of cholesterol into bile ac ids has attracted increased interest, in particular after the recent discov ery that nuclear receptors (farnesoid X receptor and liver X receptor) are involved in the regulation of bile acid synthesis. Recently, it has also be en shown that the biosynthesis of bile acids is not exclusively restricted to the liver, and that degradation may start by a hydroxylation of choleste rol in the brain or in other extrahepatic organs. During the past 2 years t he genes coding for three of the six enzymes catalysing the first steps in bile acid biosynthesis have been cloned and characterized. These genes and their gene products will be described here. Curr Opin Lipidol 12:97-103. (C ) 2001 Lippincott Williams & Wilkins.