CYP27A1 and cerebrotendinous xanthomatosis: Cerebrotendinous xanthomatosis (CTX: OMIM#213,700) is a rare autosomal-recessive lipid storage disease caused by deficiency of the mitochondrial cytochrome P 450 enzyme, sterol 27-hydroxylase (CYP27A1, EC 1.14.15.15) due to mutations in the CYP27A1 gene [1].