Genetic diagnosis of cerebrotendinous xanthomatosis

脑腱黄瘤病(CTX)是一种遗传性类固醇蓄积症。导致CTX的生化缺陷是线粒体类固醇27-羟基酶缺乏，该酶氧化与胆汁酸形成有关的胆固醇侧链。在本研究中，在3名日本CTX患者和1名CTX杂合子中发现了两个新的不同的点突变。其中两个纯合子和杂合子受试者在密码子441[CGG(Arg)to CAG(Gln)]上有一个碱基A替代G。另一纯合子在第441位密码子[CGG(Arg)to TGG(Trp)]有C到T的转换。这两个不同的突变导致了酶Stu I或Hpa II的两个限制性片段长度多态性(RFLP)。我们还使用这些患者的皮肤成纤维细胞分析了类固醇27-羟基酶的活性。虽然两个纯合子受试者的酶活性水平检测不到，但一个纯合子受试者和杂合子受试者的酶活性水平降低。这些结果表明，新发现的固醇27-羟基酶基因点突变可能是日本CTX患者中固醇270-羟基酶缺乏的原因。

Cerebrotendinous xanthomatosis (CTX) is a hereditary sterol storage disease. The biochemical defect that causes CTX is a deficiency of the mitochondrial sterol 27-hydroxylase which oxidizes the side chain of cholesterol in connection with formation of bile acids. In the present study two new different point mutations are found in the heme-ligand binding domain of the sterol 27-hydroxylase gene in three Japanese CTX patients and one CTX heterozygote. Two of the homozygotes as well as the heterozygote subject have a single base substitution of A for G at codon 441 [CGG(Arg) to CAG(Gln)]. Another homozygote has a transition of C to T at codon 441 [CGG(Arg) to TGG(Trp)]. These two different mutations result in two restriction fragment length polymorphisms (RFLPs) for the enzymes Stu I or Hpa II.We also assayd sterol 27-hydroxylase activity using skin fibroblasts from these patients. While two of the homozygous subjects have undetectable levels of the enzyme activity, one homozygous and heterozygous subjects have decreased levels of the enzyme activity. These results suggest that the newly identified point mutations in the sterol 27-hydroxylase gene could account for the sterol 270-hydroxylase deficiency in the Japanese CTX patients.