Genetic diagnosis of cerebrotendinous xanthomatosis

脑腱黄瘤病是一种遗传性胆固醇沉积病。导致CTX的生化缺陷是线粒体固醇27-羟化酶的缺乏，该酶氧化与胆汁酸形成有关的胆固醇的侧链。在本研究中，发现两个新的不同的点突变在血红素配体结合结构域的甾醇27-羟化酶基因在三个日本CTX患者和一个CTX杂合子。两个纯合子以及杂合子受试者在密码子441处具有A对G的单碱基取代[CGG（Arg）至CAG（Gln）]。另一个纯合子在密码子441处具有C到T的转变[CGG（Arg）到TGG（Trp）]。这两种不同的突变导致酶Stu I或Hpa II的两种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测定了甾醇27-羟化酶的活性。虽然两个纯合受试者具有不可检测的酶活性水平，但一个纯合和杂合受试者具有降低的酶活性水平。这些结果表明，在甾醇27-羟化酶基因中新发现的点突变可以解释日本CTX患者的甾醇270-羟化酶缺乏症。

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.