Wani Aijaz A, Ahanger Sajad H, Bapat Sharmila A, Rangrez Ashraf Y, Hingankar Nitin, Suresh C G, Barnabas Shama, Patole Milind S, Shouche Yogesh S
National Centre for Cell Science, Pune, India.
PLoS One. 2007 Sep 26;2(9):e942. doi: 10.1371/journal.pone.0000942.
Mitochondrial encephalomyopathies are a heterogeneous group of clinical disorders generally caused due to mutations in either mitochondrial DNA (mtDNA) or nuclear genes encoding oxidative phosphorylation (OXPHOS). We analyzed the mtDNA sequences from a group of 23 pediatric patients with clinical and morphological features of mitochondrial encephalopathies and tried to establish a relationship of identified variants with the disease.
METHODOLOGY/PRINCIPLE FINDINGS: Complete mitochondrial genomes were amplified by PCR and sequenced by automated DNA sequencing. Sequencing data was analyzed by SeqScape software and also confirmed by BLASTn program. Nucleotide sequences were compared with the revised Cambridge reference sequence (CRS) and sequences present in mitochondrial databases. The data obtained shows that a number of known and novel mtDNA variants were associated with the disease. Most of the non-synonymous variants were heteroplasmic (A4136G, A9194G and T11916A) suggesting their possibility of being pathogenic in nature. Some of the missense variants although homoplasmic were showing changes in highly conserved amino acids (T3394C, T3866C, and G9804A) and were previously identified with diseased conditions. Similarly, two other variants found in tRNA genes (G5783A and C8309T) could alter the secondary structure of Cys-tRNA and Lys-tRNA. Most of the variants occurred in single cases; however, a few occurred in more than one case (e.g. G5783A and A10149T).
The mtDNA variants identified in this study could be the possible cause of mitochondrial encephalomyopathies with childhood onset in the patient group. Our study further strengthens the pathogenic score of known variants previously reported as provisionally pathogenic in mitochondrial diseases. The novel variants found in the present study can be potential candidates for further investigations to establish the relationship between their incidence and role in expressing the disease phenotype. This study will be useful in genetic diagnosis and counseling of mitochondrial diseases in India as well as worldwide.
线粒体脑肌病是一组异质性临床疾病，通常由线粒体DNA（mtDNA）或编码氧化磷酸化（OXPHOS）的核基因发生突变所致。我们分析了一组23例具有线粒体脑肌病临床和形态学特征的儿科患者的mtDNA序列，并试图确定所鉴定变异与该疾病的关系。
方法/主要发现：通过聚合酶链反应（PCR）扩增完整的线粒体基因组，并通过自动DNA测序进行测序。测序数据由SeqScape软件分析，并通过BLASTn程序进行确认。将核苷酸序列与修订后的剑桥参考序列（CRS）以及线粒体数据库中存在的序列进行比较。获得的数据表明，许多已知和新的mtDNA变异与该疾病相关。大多数非同义变异是异质性的（A4136G、A9194G和T11916A），表明它们在本质上可能具有致病性。一些错义变异虽然是纯质性的，但在高度保守的氨基酸处出现了变化（T3394C、T3866C和G9804A），并且先前已在患病情况下被鉴定出来。同样，在tRNA基因中发现的另外两个变异（G5783A和C8309T）可能会改变半胱氨酸tRNA和赖氨酸tRNA的二级结构。大多数变异仅在单个病例中出现；然而，有少数在不止一个病例中出现（例如G5783A和A10149T）。
本研究中鉴定的mtDNA变异可能是该患者组儿童期发病的线粒体脑肌病的可能病因。我们的研究进一步强化了先前报道的在线粒体疾病中被暂定致病的已知变异的致病评分。本研究中发现的新变异可能是进一步研究的潜在候选对象，以确定它们的发生率与表达疾病表型的作用之间的关系。这项研究将有助于印度以及全球范围内线粒体疾病的基因诊断和咨询。
