4 NOVEL MUTATIONS OF STEROL 27-HYDROXYLASE GENE IN ITALIAN PATIENTS WITH CEREBROTENDINOUS XANTHOMATOSIS

We report the characterization of eight mutations of sterol 27-hydroxy lase gene (CYP27) in five Italian patients with cerebrotendinous xanth omatosis, who were found to be compound heterozygotes. Four mutations (C --> T at nt 45 of exon 4, G(+1) --> A in intron 6, G(+5) --> T in i ntron 7, and G(-1) --> A in intron 7) are novel. The C --> T at nt 45 of exon 4 converts tile arginine codon into a stop codon thus generati ng a truncated protein of 198 amino acids. The three splice site mutat ions reduced the content of CYP27 mRNA in skill fibroblasts to very lo w or undetectable levels and generated minute amounts of abnormal mRNA s. The G(+1) --> A transition in intron 6 produced three abnormal mRNA s. In the first, the 5' half of exon 6 joins to exon 7, skipping 89 bp of exon 6, and in the second, exon 5 joins directly to exon 7. The pr edicted translation products of these mRNAs are truncated proteins. In the third abnormal mRNA, exon 5 joins to exon 8 with an in-frame dele tion of 246 bp. The G(+5) --> T transversion in intron 7 generates a s ingle abnormal mRNA in which exon 6 joins directly to exon 8, with a f rameshift and a premature stop codon. In the G(-1) --> A transition in intron 7, two mRNAs are generated. In the first, the retention of the whole intron 7 causes a frameshift and a premature stop codon; in the second, the joining of exon 7 to exon 8 is associated with an in-fram e deletion of the first 6 nucleotides. All these novel mutations are p redicted to produce structurally abnormal enzymatic proteins with no m easurable biological activity.