中国人Machado-Joseph病四例患者不同组织CAG重复序列的研究

The study on CAG repeat sequence of various tissues from four cases of Chinese Machado-Joseph disease

目的研究和比较4例中国人Machado-Joseph病（MJD）患者体内30多种组织的CAG重复数目，探讨CAG重复扩展与MJD的致病机制和选择性病理损害之间的关系。方法选取中枢神经系统、外周神经、内脏、肌肉、皮肤等30多种部位的组织，采用标准的酚－氯仿抽提法从中提取基因组DNA，再用聚合酶链反应法对致病的MJD基因内的CAG重复序列进行扩增，最后进行变性聚丙烯酰胶凝胶电泳和放射自显影法测定并比较不同组织CAG重复数目。结果4例MJD患者CAG重复数目（致病基因／正常基因）分别是79／14，76／15，78／15，77／15，每例患者不同组织的CAG重复数目没有差异，未能发现体细胞镶嵌现象。结论MJD患者各种组织的CAG重复扩展无差别，但是CAG重复序列和其编码的多聚谷氨酰胺链在病变神经元和其他正常组织细胞中所起的作用不同；组织细胞对CAG重复序列和其表达产物多聚谷氨酰胺链致病作用的易患性可能在MJD病变中起重要作用。

Objective The range of CAG repeat sequences from various tissues in 4 cases of Chinese Machado-Joseph disease(MJD) was determined. The pathogenesis of MJD and the relationahip between the CAG repeat expansions and the selective distribution of pathological damage were also explored. Methods 1. The tissues from more than 30 positions such as the central nervous system, the peripheral nerves, the viscere, the muscles and the skin on were picked out. 2. Genomic DNA was extracted from these tissues with standard procedures. 3. The polymerase chain reaction(PCR) was used to amplify the CAG repeat sequence inside the causatie MJD1 gene.4. The size of CAG repea of every tissue was determined and compared with each other by electrophoresis through denaturing polyacrylamide gels and autoradiography. Results The sizes of CAG repeat sequence on the alleles of each patient were respectively 79/14,76/15,78/15 and 77/15. The sizes of CAG repeat sequence from various tissues in every patient had no diversity. Somatic mosaicism could not be found in the 4 patients. Conclusion Although the CAG repeat expansions among various tissues were not different, effect of CAG repeat sequence and polyglutamine stretch it coded on the affected neurons differed from the normal tissues.The vulnerability of the affected tissues to the pathogenic effect of CAG repeat and poluglutamine stretch would play an important role in the MJD pathological damage. This study might provide a basis for further exploration of the pathogenesis of MJD and suggest the relationship between CAG repeat sequence and specific pathological damage of the disease.