Hammans S R, Sweeney M G, Wicks D A, Morgan-Hughes J A, Harding A E
University Department of Clinical Neurology, Institute of Neurology, London, UK.
Brain. 1992 Apr;115 ( Pt 2):343-65. doi: 10.1093/brain/115.2.343.
Using in situ hybridization and histochemistry we have studied muscle biopsy samples from eight patients with mitochondrial encephalomyopathies and known defects of mitochondrial DNA (mtDNA). In four patients with heteroplasmic mtDNA deletions there were focal accumulations of deleted mtDNA and its transcripts within ragged red fibres (RRF). In one of these, a probe designed specifically to detect deleted mtDNA identified abundant deleted mtDNA and its fusion transcript in RRF and lesser accumulations in non-ragged red cytochrome oxidase (COX) deficient fibres. A further patient with a deletion involving the heavy strand promoter region showed accumulation of deleted mtDNA and light strand transcripts in RRF, but concomitant depletion of all heavy strand transcripts. In all patients with deletions, normal mtDNA transcripts were depleted in COX deficient fibres irrespective of ragged red change. Deleted mtDNA was rare or absent in normal fibres. Within RRF, COX activity was more profoundly impaired in patients with deletions involving COX subunits. In two patients heteroplasmic for the base pair (bp) 3243 mutation associated with mitochondrial myopathy, encephalopathy, lactic acidosis and strokelike episodes (MELAS), RRF contained a great excess of mtDNA and transcripts of all species. Some RRF showed excess COX activity. Non-ragged red COX deficient fibres showed equal increases of ribosomal RNA (rRNA) and messenger RNA, suggesting that focal biochemical defects were not associated with a quantitative defect of transcription termination at the 3' end of the 16S rRNA which might be predicted. A patient heteroplasmic for the bp 8344 mutation (associated with myoclonic epilepsy and ragged red fibres: MERRF) showed subnormal COX activity within RRF, although the tissue distribution of mtDNA and its transcripts was similar to that seen with the bp 3243 mutation. Within mitochondrial encephalomyopathies, the relationships between the distribution and expression of abnormal mtDNA and the focal biochemical consequences are complex and heterogeneous.
我们运用原位杂交和组织化学技术，研究了8例患有线粒体脑肌病且已知存在线粒体DNA（mtDNA）缺陷的患者的肌肉活检样本。在4例存在异质性mtDNA缺失的患者中，缺失的mtDNA及其转录本在破碎红纤维（RRF）中呈局灶性积聚。其中1例患者，专门设计用于检测缺失mtDNA的探针在RRF中鉴定出大量缺失的mtDNA及其融合转录本，在非破碎的红色细胞色素氧化酶（COX）缺陷纤维中积聚较少。另1例涉及重链启动子区域缺失的患者，在RRF中显示出缺失的mtDNA和轻链转录本的积聚，但所有重链转录本同时减少。在所有缺失患者中，无论有无破碎红改变，COX缺陷纤维中的正常mtDNA转录本均减少。正常纤维中缺失的mtDNA罕见或不存在。在RRF内，涉及COX亚基缺失的患者中COX活性受损更为严重。在2例因与线粒体肌病、脑病、乳酸酸中毒和卒中样发作（MELAS）相关的3243碱基对（bp）突变而呈异质性的患者中，RRF含有大量过量的mtDNA和所有种类的转录本。一些RRF显示出COX活性过高。非破碎的红色COX缺陷纤维显示核糖体RNA（rRNA）和信使RNA等量增加，这表明局灶性生化缺陷与16S rRNA 3'端转录终止的定量缺陷无关，而这是可能被预测到的。1例因8344 bp突变（与肌阵挛性癫痫和破碎红纤维相关：MERRF）而呈异质性的患者，其RRF内COX活性低于正常，尽管mtDNA及其转录本的组织分布与3243 bp突变所见相似。在线粒体脑肌病中，异常mtDNA的分布与表达和局灶性生化后果之间的关系复杂且具有异质性。
