A case of sudden cardiac death due to mitochondrial disease

A 25-year-old, emaciated man without medical treatment was found to have died suddenly at home by his mother. At autopsy, there were no injuries to his body, but significant circulatory insufficiency was observed. Electron microscopy revealed abnormal mitochondria in cells of the cardiac conduction system. The conduction system was filled with mitochondrial size abnormalities and mitochondrial cristae abnormalities. No notable abnormal findings were observed in other organs. Genetic examination of the blood revealed the mitochondrial pathogenetic variant m.3243A>G. Epileptic seizures, diabetic ketoacidosis, and hyperosmolar hyperglycemic state were unlikely to be the cause of sudden death. The cause of death was diagnosed as arrhythmia possibly induced by the failure of the cardiac conduction system due to mitochondrial disease. This is a rare case of sudden death caused by an accumulation of abnormal mitochondria in the cardiac conduction system.     

Creatine has no beneficial effect on skeletal muscle energy metabolism in patients with single mitochondrial DNA deletions: a placebo-controlled, double-blind 31P-MRS crossover study

The purpose of our randomized, double-blind, placebo-controlled crossover study in 15 patients with chronic progressive external ophthalmoplegia (CPEO) or Kearns-Sayre syndrome (KSS) because of single large-scale mitochondrial (mt) DNA deletions was to determine whether oral creatine (Cr) monohydrate can improve skeletal muscle energy metabolism in vivo. Each treatment phase with Cr in a dosage of 150 mg/kg body weight/day or placebo lasted 6 weeks. The effect of Cr was estimated by phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS), clinical and laboratory tests. (31)P-MRS analysis prior to treatment showed clear evidence of severe mitochondrial dysfunction. However, there were no relevant changes in (31)P-MRS parameters under Cr. In particular, phosphocreatine (PCr)/ATP at rest did not increase, and there was no facilitation of post-exercise PCr recovery. Clinical scores and laboratory tests did not alter significantly under Cr, which was tolerated without major side-effects in all patients. Cr supplementation did not improve skeletal muscle oxidative phosphorylation in our series of patients. However, one explanation for our negative findings may be the short study duration or the limited number of patients included.     

线粒体DNA 16519 T→C变异与肺癌易感性的关系

[目的] 探讨线粒体DNA(mtDNA)16519 T→C变异与肺癌易感性的关系.[方法] 采用1∶1病例对照研究,选择南京市原发性肺癌病人与对照各50例,提取血标本白细胞DNA,通过PCR-RFLP法分析mtDNA 16519 T→C变异与肺癌易感性的相关性.[结果] mtDNA 16519 T→C变异在肺癌病人中的发生率为64%,显著高于对照的42%(χ2＝4.48,P＜0.05),与肺癌发生呈现相关性(OR＝2.38, 95%CI:1.07～5.31).与代谢酶GSTT1缺失型、mEH-exon4突变型存在协同作用(OR＝2.55, 95%CI:1.02～6.40).联合筛检串联试验结果显示,同时考虑16519位点和GSTT1基因型检测结果时,可提高肺癌易感性检测的特异度.[结论] mtDNA 16519 T→C变异可能通过改变线粒体的功能使患肺癌的危险性增高,mtDNA16519位点突变与GSTT1、mEH-exon4突变对肺癌发生有协同作用.在肺癌遗传易感性的检测中,应进行易感基因型的联合检测.     

The genes for cytochrome b,ND 4L,ND6 and two tRNAs from the mitochondrial genome of the locust,Locusta migratoria

We have cloned and characterized a 2,778-kb XbaI segment of the mitochondrial genome of the locust, Locusta migratoria. It harbours portions of the ND4 and the ND1 genes, the entire genes for ND6, ND4L and cytochrome b, and the genes for three mitochondrial tRNAs. The genes are arranged in an order which is conserved between orthopteran and dipteran insects. The analysis of the cytochrome b sequence, and its comparison with other systems, supports the current model structure for this polypeptide.     

Mitochondrial DNA sequences reveal close relationships between social parasitic ants and their host species

In the tribe Leptothoracini, the phylogenetic relationship of socially parasitic ants (Doronomyrmex kutteri, D. goesswaldi and Harpagoxenus sublaevis) and their host species Leptothorax acervorum has been controversial. Even more controversial is the relationship between the socially parasitic ant Chalepoxenus muellerianus and its host species Leptothorax unifasciatus, L. nigriceps, L. interruptus and L. recedens. On the basis of morphological, ecological and ethological criteria it has been argued that socially parasitic ants and their respective hosts always evolved from common ancestors, and hence it has been postulated that these species should be included in common taxonomical groups. This would require the division of the tribe Leptothoracini into two subgroups, one comprising the subgenus Leptothorax (s. str.) and the other the subgenus Myrafant, together with their respective parasitic genera. We have used the polymerase chain reaction (PCR) to compare a 360-bp sequence of the mitochondrial cytochrome b gene of 14 species belonging to the tribe Leptothoracini and an outgroup species Tetranorium impurum (Tetramoriini). The results generally agree with the morphological studies which suggest that a common ancestral species differentiated into host and parasite species. This relationship is very obvious within the Leptothorax (s. str.) group but less pronounced in the species belonging to the Myrafant group. Leptothorax (Temnothorax) recedens shows a greater sequence divergence than the outgroup species T. impurum.     

Cytoplasmic male sterility is associated with large deletions in the mitochondrial DNA of two Nicotiana sylvestris protoclones

Summary Two cytoplasmic male-sterile plants (CMSI and CMSII) were obtained by protoplast culture in Nicotiana sylvestris. Both plants showed large deletions (up to 50 kb) in their mitochondrial DNA. Restriction maps of the reorganized regions suggested that the deletions occurred via two homologous recombination events (rec. 1 and rec. 2) in the parental mitochondrial genome. With the exception of nad5, no mitochondrial DNA polymorphism could be detected between parental and CMS lines using different heterologous genes probes. A sequence homologous to the Oenothera nad5 mitochondrial gene was located close to the CMSI-specific rec. 2 region. Moreover, a cDNA probe corresponding to total mitochondrial RNA from the parent line was found to hybridize to mitochondrial DNA fragments involved in the rec. 1 event common to both CMS lines, suggesting that rec. 1 lies in a transcribed region. Cytoplasmic male sterility in the Nicotiana sylvestris CMS mutants could be due either to gene deletion or to a regulatory effect of such a deletion on mitochondrial gene expression, rather than to the presence of specific polypeptides as has been shown in the T cytoplasm of maize, or in CMS Petunia.     

Phylogenetic analysis of mtDNA haplogroup TJ in a Finnish population

An association between mitochondrial DNA (mtDNA) mutations 11778G>A and 14484T>C and mtDNA haplogroup J suggests that this haplogroup harbors substitutions capable of modifying the phenotype of Leber's disease. Our knowledge of the compilation of substitutions in haplogroup J is based on only a small number of complete mtDNA sequences, however. We constructed phylogenetic networks for mtDNA haplogroup TJ that were based on the sequence of the complete coding region and the hypervariable segment I, respectively, in 28 Finnish samples. The networks revealed a subdivision of the haplogroup into subclusters T1, T2, J1, and J2, while comparison of the two networks suggested nine fast evolving nucleotide sites in the hypervariable segment I. Genotypes of patients harboring 11778G>A or 14484T>C were obtained from the literature and were then placed in the network. Only four substitutions were found to be common to the patients, but none of these was unique to haplogroup J. If increased penetrance of the 11778G>A and 14484T>C mutations in patients belonging to haplogroup J is assumed, combinations of ancient substitutions must be implicated. Received: September 29, 2000 / Accepted: November 10, 2000     

Sequence analysis of cDNAs for the human and bovine ATP synthase β subunit: mitochondrial DNA genes sustain seventeen times more mutations

We have cloned and sequenced human and bovine cDNAs for the subunit of the ATP synthase (ATP-synß), a nuclear DNA (nDNA) encoded oxidative phosphorylation (OXPHOS) gene. The two cDNAs were found to share 99% amino acid homology and 94% nucleotide homology. The evolutionary rate of ATPsynß was then compared with that of two mitochondrial DNA (mtDNA) ATP synthase genes (ATPase 6 and 8), seven other mtDNA OXPHOS genes, and a number of nuclear genes. The synonymous substitution rate for ATPsynß proved to be 1.9 × 10^–9 substitutions per site per year (substitutions × site^–1 × year^–1) (SSY). This is less than 1/2 that of the average nDNA gene, 1/12 the rate of ATPase 6 and 8, and 1/17 the rate of the average mtDNA gene. The synonymous and replacement substitution rates were used to calculate a new parameter, the selective constraint ratio. This revealed that even the most variable mtDNA protein was more constrained than the average nDNA protein. Thus, the high substitution mutation rate and strong selective constraints of mammalian mtDNA proteins suggest that mtDNA mutations may result in a disproportionately large number of human hereditary diseases of OXPHOS.     

Presence of a linear plasmid-like DNA molecule in the fungal pathogen Ceratocystis fimbriata Ell. & Halst.

Summary A plasmid-like molecule was detected in a strain of the ascomycete Ceratocystis fimbriata Ell. & Halst., a pathogenic fungus of Populus spp. The DNA replicon, designated pFQ501, was found to have a linear structure with a length of 6.0 kb (3.9 × 10⁶ daltons) and a density of 1.685 g/cc. This molecule was found to be associated with the mitochondria and was isolated from the gel; its restriction map was deduced from single and double digestions.     

Location,identity, amount and serial entry of chloroplast DNA sequences in crucifer mitochondrial DNAs

Southern blot hybridization techniques were used to examine the chloroplast DNA (cpDNA) sequences present in the mitochondrial DNAs (mtDNAs) of two Brassica species (B. campestris and B. hirta), two closely related species belonging to the same tribe as Brassica (Raphanus sativa, Crambe abyssinica), and two more distantly related species of crucifers (Arabidopsis thaliana, Capsella bursa-pastoris). The two Brassica species and R. sativa contain roughly equal amounts (12–14 kb) of cpDNA sequences integrated within their 208–242 kb mtDNAs. Furthermore, the 11 identified regions of transferred DNA, which include the 5 end of the chloroplast psaA gene and the central segment of rpoB, have the same mtDNA locations in these three species. Crambe abyssinica mtDNA has the same complement of cpDNA sequences, plus an additional major region of cpDNA sequence similarity which includes the 16S rRNA gene. Therefore, except for the more recently arrived 16S rRNA gene, all of these cpDNA sequences appear to have entered the mitochondrial genome in the common ancestor of these three genera. The mitochondrial genomes of A. thaliana and Capsella bursa-pastoris contain significantly less cpDNA (5–7 kb) than the four other mtDNAs. However, certain cpDNA sequences, including the central portion of the rbcL gene and the 3 end of the psaA gene, are shared by all six crucifer mtDNAs and appear to have been transferred in a common ancestor of the crucifer family over 30 million years ago. 1n conclusion, DNA has been transferred sequentially from the chloroplast to the mitochondrion during crucifer evolution and these cpDNA sequences can persist in the mitochondrial genome over long periods of evolutionary time.