CEREBROTENDINOUS XANTHOMATOSIS CAUSED BY 2 NEW MUTATIONS OF THE STEROL-27-HYDROXYLASE GENE THAT DISRUPT MESSENGER-RNA SPLICING

Cerebrotendinous xanthomatosis (CTX) is an inherited sterol storage di sease associated with the accumulation of cholestanol and cholesterol in various tissues. CTX is caused by a deficiency of sterol-27-hydroxy lase, a mitochondrial enzyme that oxidizes the side chain of cholester ol in the pathway leading to the formation of bile acids. In the prese nt study we report two mutations of sterol-27-hydroxylase gene (CYP27 gene) found in Italian CTX patients. Proband T.C. is homozygous for a G --> A transition at the first nucleotide of intron 7. This mutation causes the formation of minute amounts of an abnormal mRNA, in which e xon 6 joins directly to exon 8 with the skipping of exon 7. The exon 6 -exon 8 junction results in a frame shift, downstream from the codon f or Arg(362), which generates a string of 28 novel amino acids precedin g a premature termination codon. Proband C.U. is homozygous for a G -- > C transversion at the last nucleotide of exon 3. This mutation, whic h changes the consensus sequence of the 5' donor splice site, is assoc iated with barely detectable levels of sterol-27-hydroxylase mRNA, of normal size, in proband fibroblasts. As both mutations change the site s for two restriction enzymes, rapid methods were devised for the iden tification of the healthy carriers among the probands' family members and for the screening of these mutations in other CTX patients.