Age-dependent 6kb deletion in human liver mitochondrial DNA.

Using PCR technique, restriction mapping and DNA sequencing, we analyzed liver mitochondrial DNA (mtDNA) of 2 stillborn babies and 62 Chinese subjects with non-liver disease from 27 to 86 years old. The results showed an age-dependent 6,063 bp deletion in the liver mtDNA of older subjects. We found a TAACAGAC sequence flanking the 5'-end breakpoint at 7,842 nucleotide position and an imperfect repeat sequence CAACATAC flanking the 3'-end breakpoint at 13,905 nucleotide position. The incidence of the deleted mtDNA was found to increase with age. The deleted mtDNA was not detected in the liver of the stillbirth or blood cells of all the subjects. This is the first account that an age-related 6,063 bp deletion occurs in the liver mtDNA of old humans. The occurrence of this and previously reported 4,977 bp deletions is consistent with our recent finding that liver mitochondrial respiratory functions decline with age and support the hypothesis that continuous accumulation of mtDNA mutations is an important contributor to ageing process in the human.     

Sequence homology at the breakpoint and clinical phenotype of mitochondrial DNA deletion syndromes

Mitochondrial DNA (mtDNA) deletions are a common cause of mitochondrial disorders. Large mtDNA deletions can lead to a broad spectrum of clinical features with different age of onset, ranging from mild mitochondrial myopathies (MM), progressive external ophthalmoplegia (PEO), and Kearns-Sayre syndrome (KSS), to severe Pearson syndrome. The aim of this study is to investigate the molecular signatures surrounding the deletion breakpoints and their association with the clinical phenotype and age at onset. MtDNA deletions in 67 patients were characterized using array comparative genomic hybridization (aCGH) followed by PCR-sequencing of the deletion junctions. Sequence homology including both perfect and imperfect short repeats flanking the deletion regions were analyzed and correlated with clinical features and patients' age group. In all age groups, there was a significant increase in sequence homology flanking the deletion compared to mtDNA background. The youngest patient group (<6 years old) showed a diffused pattern of deletion distribution in size and locations, with a significantly lower sequence homology flanking the deletion, and the highest percentage of deletion mutant heteroplasmy. The older age groups showed rather discrete pattern of deletions with 44% of all patients over 6 years old carrying the most common 5 kb mtDNA deletion, which was found mostly in muscle specimens (22/41). Only 15% (3/20) of the young patients (<6 years old) carry the 5 kb common deletion, which is usually present in blood rather than muscle. This group of patients predominantly (16 out of 17) exhibit multisystem disorder and/or Pearson syndrome, while older patients had predominantly neuromuscular manifestations including KSS, PEO, and MM. In conclusion, sequence homology at the deletion flanking regions is a consistent feature of mtDNA deletions. Decreased levels of sequence homology and increased levels of deletion mutant heteroplasmy appear to correlate with earlier onset and more severe disease with multisystem involvement.     

Age-related mitochondrial genotypic and phenotypic alterations in human skeletal muscle

To have a clearer picture of how mitochondrial damages are associated to aging, a comprehensive study of phenotypic and genotypic alterations was carried out, analyzing with histochemical and molecular biology techniques the same skeletal muscle specimens of a large number of healthy subjects from 13 to 92 years old. Histochemical data showed that ragged red fibers (RRF) appear at about 40 years of age and are mostly cytochrome c oxidase (COX)-positive, whereas they are almost all COX-negative thereafter. Molecular analyses showed that the 4977 bp deletion of mitochondrial DNA (mtDNA(4977)) and the 7436 bp deletion of mtDNA (mtDNA(7436)) are already present in individuals younger than 40 years of age, but their occurrence does not change with age. After 40 years of age the number of mtDNA deleted species, as revealed by Long Extension PCR (LX-PCR), increases, the 10422 bp deletion of mtDNA (mtDNA(10422)) appears, although with a very low frequency of occurrence, and mtDNA content is more than doubled. Furthermore, mtDNA(4977) level directly correlates with that of COX-negative fibers in the same analyzed subjects. These data clearly show that, after 40 years of age, the phenotypic and genotypic mitochondrial alterations here studied appear in human skeletal muscle and that they are closely related.     

Differential accumulations of 4,977 bp deletion in mitochondrial DNA of various tissues in human ageing

Several types of deletions in mitochondrial DNA (mtDNA) have been recetly identified in various tissues of old humans. In order to determine whether there are differences in the incidence and proportion of deleted mtDNAs in different tissues during human ageing, we examined tha 4,977 bp deletion in mtDNA of various tissues from subjects of different ages. Total DNA was extracted from each of the biopsied tissues and was serially diluted by two-fold with distilled water. A 533 bp DNA fragment was amplified by PCR from total mtDNA using a pair of primers L3304-3323 and H3817-3836, and another 524 bp PCR product was amplified from 4,977 bp deleted mtDNA by identical conditions using another pair of primers L8150-8166 and H13631-13650. The maximum dilution fold of each sample that still allowed the ethidium bromide-stained PCR product (533 bp or 524 bp) in the agarose gel to be visible under UV light illumination was taken as the relative abundance of the mtDNA (wild-type or mutant) in the original sample. By this method, we were able to determine the proportion of deleted mtDNA in human tissues. We found that the 4,977 bp deletion started to appear in the second and third decades of life in human muscle and liver tissues. But the deletion was not detectable in the testis until the age of 60 years. Moreover, the proportion of deleted mtDNA varied greatly in different tissues. Among the tissues examined, muscle was found to harbor higher proportin of deleted mtDNA than the other tissues. The average proportion of the 4,977 bp depleted mtDNA of the muscle from subjects over 70 years old was approximately 0.06%, and that of the liver and the testis was 0.0076% and 0.05%, respectively. These findings suggest that the frequency and proportion of the deleted mtDNA in human tissues increase with age and that the mtDNA deletions occur more frequently and abundantly in high energy-demanding tissues during the ageing process of the human.     

Quantitative analysis of age-associated accumulation of mitochondrial DNA with deletion in human hearts

We have demonstrated that myocardial mitochondrial DNA (mtDNA) with a 7,436 base-pair deletion existed in all subjects that were over 70 years old. Since each mitochondrion has two or three copies of its own DNA, quantitative analysis is required for the evaluation of the role of mtDNA with deletions in the age-related deterioration of cardiac performance. For this purpose, the kinetic polymerase chain reaction (PCR) method developed in our laboratory was used in this investigation to determine myocardial mtDNA with this 7,436 base-pair deletion in human cadavers of various ages. The mtDNA population with this deletion increased exponentially with age [log f (% of deleted mtDNA) = -3.136 + 0.0454 x age, r = 0.95, P less than 0.01)], and was estimated at 3% and 9% in subjects of age 80 and 90, respectively. The deleted portion encodes 7 subunits of the mitochondrial ATP production system, and a population of mtDNA with this deletion over a certain threshold might induce a significant deterioration of cardiac energy metabolism. Cardiac function is known to deteriorate with age, and an increase in the population of mtDNA with deletion is likely to be an important contributing factor to aged heart (presbycardia).     

Detection of mtDNA with 4977 bp deletion in blood cells and atherosclerotic lesions of patients with coronary artery disease

Recent evidence suggests that somatic mutations in nuclear and mitochondrial DNA accumulated during aging, may significantly contribute to the pathogenesis of chronic-degenerative illness such as coronary artery disease (CAD). Mitochondrial DNA with 4977 bp deletion mutation (mtDNA4977) is a common type of mtDNA alteration in humans. However, little attempt has been made to detect the presence of mtDNA4977 deletion in cells and tissues of cardiovascular patients. This study investigated the presence of mtDNA4977 in blood samples of 65 cardiovascular patients and 23 atherosclerotic plaques of human coronaries with severe atherosclerosis. Moreover, the presence of the deletion has been investigated in blood cells from 22 healthy age-matched subjects. The detection of mtDNA4977 has been performed by using a nested polymerase chain reaction (PCR) protocol and normalized to wild-type mtDNA. A significant higher incidence of mtDNA4977 was observed in CAD patients with respect to healthy subjects (26.2% versus 4.5%; P=0.03). Furthermore, the relative amount of the deletion was significantly higher in the patients compared to the control group (P=0.02). The mtDNA4977 was detected in 17 of the 65 patients blood samples (26.2%) and deletion levels ranged from 0.18 to 0.46% of the total mtDNA (mean: 0.34+/-0.02%). For what concerns atherosclerotic lesions, 5 patients (21.7%) showed the deletion ranging from 0.13 to 0.45% of the total mtDNA (mean: 0.35+/-0.06%). In both samples from patients, the incidence and the relative amount of mtDNA4977 was not significantly influenced by atherogenic risk factors and clinical parameters. The obtained results may suggest that the increase of oxidative stress in cardiovascular disease may be responsible for the accumulation of mtDNA damage in coronary artery disease patients.     

鼠毛及脑线粒体DNA片段缺失与增龄的关系

以聚合酶链反应（ＰＣＲ）技术检测不同年龄Ｂａｌｂ／ｃ小鼠脑细胞线粒体ＤＮＡ片段缺失与增龄的关系．发现老年鼠脑细胞线粒体３８６７ｂｐ片段缺失率为５０％;而断奶鼠与青年鼠均无此缺失片段出现;用鼠毛为材料进行无损伤检测亦获类似的结果．有人认为线粒体ＤＮＡ片段缺失率可作为生物衰老的一种生物学标志     

The effect of chronic alcohol consumption on mitochondrial DNA mutagenesis in human blood

The 4977bp deletion of mitochondrial DNA (mtDNA) is known to accumulate with increasing age in post mitotic tissues. Recently, studies came out detecting this specific alteration also in fast replicating cells, e.g. in blood or skin tissue, often in correlation to specific diseases or -- specifically in skin -- external stressors such as UV radiation. In this study, we investigated mitochondrial mutagenesis in 69 patients with a chronic alcoholic disease and 46 age matched controls with a moderate drinking behavior. Two different fragments, specific for total and for deleted mtDNA (dmtDNA) were amplified in a duplex-PCR. A subsequent fragment analysis was performed and for relative quantification, the quotient of the peak areas of amplification products specific for deleted and total mtDNA was determined. Additionally, a real time PCR was performed to quantify mtDNA copy number. The relative amount of 4977bp deleted mtDNA in alcoholics was significantly increased compared to controls. On the other hand, no difference regarding the mtDNA/nuclear DNA ratio in both investigated groups was detected. Additionally, no age dependence could be found nor in alcoholics, neither in the control group. These findings indicate that mtDNA mutagenesis in blood can be influenced by stressors such as alcohol. Ethanol seems to be a significant factor to alter mitochondrial DNA in blood and might be an additional contributor for the cellular aging process.     

Random mtDNA deletions and functional consequence in aged human skeletal muscle

Mitochondrial respiratory chain deteriorates with age, mostly in tissues with high energy requirements. Damage to mitochondrial DNA (mtDNA) by reactive oxygen species is thought to contribute primarily to this impairment. However, the overall extent of random mtDNA mutations has still not been evaluated. We carried out molecular and biochemical analyses in muscle biopsies from healthy young and aged subjects. Deleted mtDNA accumulation was followed by both quantitative PCR analysis to quantify total mtDNA, and Southern-blotting, to determine deleted to full length mtDNA ratio. Enzymatic activities of the mitochondrial respiratory chain were measured in all subjects. Randomly deleted mtDNA appeared mainly in the oldest subjects (beyond 80 years old), affecting up to 70% of mtDNA molecules. The activities of complexes III and IV of the respiratory chain, complexes with mtDNA encoded subunits, are lower in the aged subjects. Physical activity could be one major parameter modulating the mitochondrial respiratory chain activity in aged muscle.     

Large-scale mitochondrial DNA deletions in skeletal muscle of patients with end-stage renal disease

End-stage renal disease (ESRD) is associated with enhanced oxidative stress. This disease state provides a unique system for investigating the deleterious effect of exogenous sources of free radicals and reactive oxygen species (ROS) on mitochondrial DNA (mtDNA). To test the hypothesis that uremic milieu might cause more severe damage to mtDNA, we investigated the prevalence and abundance of mtDNA deletions in the skeletal muscles of ESRD patients. The results showed that the frequencies of occurrence of the 4977 bp and 7436 bp deletions of mtDNA in the muscle tissues of the older ESRD patients were higher than those of the younger patients. The frequency of occurrence of the 4977 bp-deleted mtDNA in the muscle was 33.3% for the patients in the age group of < 40 years, 66.6% in the 41-60-year-old group, 100% in the 61-80-year-old group, and 100% in patients >80 years of age, respectively. Only 22% of the normal aged controls carried the 4977 bp mtDNA deletion, whereas 77% (17/22) of the ESRD patients exhibited the mtDNA deletion. Using a semiquantitative PCR method, we determined the proportion of the 4977 bp-deleted mtDNA from the muscles that had been confirmed to harbor the deletion. We found that the proportions of the 4977 bp-deleted mtDNA in the muscle were significantly higher than those of the aged matched controls. Using long-range PCR techniques, a distinctive array of mtDNA deletions was demonstrated in the muscle of uremic patients. In summary, we found diverse and multiple mtDNA deletions in the skeletal muscles of ESRD patients. These deletions are more prevalent and abundant in ESRD patients than those found in normal populations. Accumulation of uremic toxins and impaired free radical scavenging systems may be responsible for the increased oxidative stress in ESRD patients. Such stress may result in oxidative damage and aging-associated mutation of the mitochondrial genome.     

Mitochondrial DNA alterations as ageing-associated molecular events.

Mitochondrial DNA (mtDNA) is a naked double-stranded circular extrachromosomal genetic element continuously exposed to the matrix that contains great amounts of reactive oxygen species and free radicals. The age-dependent decline in the capability and capacity of mitochondria to dispose these oxy-radicals will render mtDNA more vulnerable to mutations during the ageing process. During the past 3 years, more than 10 different types of deletions have been identified in the mtDNA of various tissues of old humans. Some of them were found only in a certain tissue but some others appeared in more than one organ or tissue. The 4977-bp deletion is the most prevalent and abundant one among these deletions. Skeletal muscle is the target tissue of most ageing-associated mtDNA deletions and has often been found to carry multiple deletions. The onset age of the various deletions in mtDNA varies greatly with individual and type of the deletion. The 4977-bp deletion has been independently demonstrated to occur in the mtDNA of various tissues of the human in the early third decade of life. However, the 7436-bp deletion was only detected in the heart mtDNA of human subjects in their late thirties. The others appeared only in older humans over 40 years old. No apparent sex difference was found in the onset age of these ageing-associated mtDNA deletions. The various ageing-associated deletions could be classified into two groups. Most of the deletions belong to the first group, in which the 5'- and 3'-end breakpoints of the deletion are flanked by 4-bp or longer direct repeats. The deletion in the second group occurs less frequently and shows no distinct repeat sequences flanking the deletion sites. These two groups of mtDNA deletions may occur by different mechanisms. The first group is most probably caused by internal recombination or slippage mispairing during replication of mtDNA by the D-loop mechanism. The deleted mtDNA and the deleted DNA fragment may be further degraded or escape from the mitochondria and get translocated into the nucleus. The latter route has been substantiated by many observations of inserted mtDNA sequences in the nuclear DNA. Thus, the fragments of migrating mtDNA may change the information content and expression level of certain nuclear genes and thereby promote the ageing process or cause cancer. Similar ageing-associated alterations of mtDNA have also been observed in aged animals and plants. I suggest that mtDNA deletions and other mutations to be discovered are molecular events generally associated with the ageing process.     

Nanopore sequencing identifies a higher frequency and expanded spectrum of mitochondrial DNA deletion mutations in human aging

Mitochondrial DNA (mtDNA) deletion mutations cause many human diseases and are linked to age-induced mitochondrial dysfunction. Mapping the mutation spectrum and quantifying mtDNA deletion mutation frequency is challenging with next-generation sequencing methods. We hypothesized that long-read sequencing of human mtDNA across the lifespan would detect a broader spectrum of mtDNA rearrangements and provide a more accurate measurement of their frequency. We employed nanopore Cas9-targeted sequencing (nCATS) to map and quantitate mtDNA deletion mutations and develop analyses that are fit-for-purpose. We analyzed total DNA from vastus lateralis muscle in 15 males ranging from 20 to 81 years of age and substantia nigra from three 20-year-old and three 79-year-old men. We found that mtDNA deletion mutations detected by nCATS increased exponentially with age and mapped to a wider region of the mitochondrial genome than previously reported. Using simulated data, we observed that large deletions are often reported as chimeric alignments. To address this, we developed two algorithms for deletion identification which yield consistent deletion mapping and identify both previously reported and novel mtDNA deletion breakpoints. The identified mtDNA deletion frequency measured by nCATS correlates strongly with chronological age and predicts the deletion frequency as measured by digital PCR approaches. In substantia nigra, we observed a similar frequency of age-related mtDNA deletions to those observed in muscle samples, but noted a distinct spectrum of deletion breakpoints. NCATS-mtDNA sequencing allows the identification of mtDNA deletions on a single-molecule level, characterizing the strong relationship between mtDNA deletion frequency and chronological aging.     

Mitochondrial DNA deletions are associated with ischemia and aging in Balb/c mouse brain

Deletions in the mitochondrial DNA (mtDNA) of Balb/c mouse cerebrums, resembling deletions found in elderly humans or in patients with certain disorders, were detected by PCR. Analysis was carried out on mice of various ages and on mice in which the bilateral common carotid arteries had been incompletely ligated to reconstruct cerebral ischemia. A 3,867 bp mtDNA deletion was present only in old or ischemic mouse groups. Among the non-ischemic groups, it was found in 0 of 12 weaning, 0 of 12 young, and four of eight old mice. Among the ischemic groups, it was found in 12 of 17 young and 11 of 11 old mice. Moreover, the percentage of total mtDNA containing deletions was 22% for the old non-ischemic group, 37% for the young ischemic group, and 69% for the old ischemic group. In addition, PCR analysis detected two other deletions of 3,726 bp and 4,236 bp in 4 of the 11 old ischemic cerebrums. The results indicate that mtDNA deletions are associated with aging, that ischemia increases the incidence of mtDNA deletions, and that mtDNA deletions resulting from ischemia are more likely to occur in old mice than in young mice.     

Marked increase in the number and variety of mitochondrial DNA rearrangements in aging human skeletal muscle.

Several reports have shown that individual mitochondrial DNA (mtDNA) deletions accumulate with age. However, the overall extent of somatic mtDNA damage with age remains unclear. We have utilized full-length PCR to concurrently screen for multiple mtDNA rearrangements in total DNA extracted from skeletal muscle derived from physiologically normal individuals (n = 35). This revealed that both the number and variety of mtDNA rearrangements increases dramatically between young and old individuals (P < 0.0001). We further examined the mtDNA from both the younger and older subjects by Southern blot analysis and observed an age-related increase in mtDNA(s) comparable in size to mtDNA products unique to patients with known mtDNA deletions. These data imply that a wide spectrum of mtDNA rearrangements accumulate in old individuals, which correlates with the marked age related decrease in OXPHOS capacity observed in post-mitotic tissues.     

Molecular investigations of mitochondrial deletions: Evaluating the usefulness of different genetic tests

Deletions in mitochondrial DNA are a common cause of mitochondrial disorders. The molecular diagnosis of mtDNA deletions for years was based on Southern hybridization later replaced by PCR methods such as PCR with primers specific for a particular deletion (mainly the so-called common deletion of 4977bp) and long PCR. In order to evaluate the usefulness of MLPA (Multiplex Ligation-dependent Probe Amplification) in molecular diagnosis of large scale mtDNA deletions we compare four diagnostic methods: Southern hybridization, PCR, long-PCR and MLPA in a group of 16 patients with suspected deletions. Analysis was performed on blood, muscle and in one case hepatic tissue DNA. The MLPA was not able to confirm all the deletions detected by PCR methods, but due to its relative ease of processing, minimal equipment, low costs and the additional possibility to detect frequent point mtDNA mutations in one assay it is worth considering as a screening method. We recommend to always confirm MLPA results by PCR methods.     

Changes in the human mitochondrial genome after treatment of malignant disease

Mitochondrial DNA (mtDNA) is the only extrachromosomal DNA in human cells. The mitochondrial genome encodes essential information for the synthesis of the mitochondrial respiratory chain. Inherited defects of this genome are an important cause of human disease. In addition, the mitochondrial genome seems to be particularly prone to DNA damage and acquired mutations may have a role in ageing, cancer and neurodegeneration. We wished to determine if radiotherapy and chemotherapy used in the treatment of cancer could induce changes in the mitochondrial genome. Such changes would be an important genetic marker of DNA damage and may explain some of the adverse effects of treatment. We studied samples from patients who had received radiotherapy and chemotherapy for point mutations within the mtDNA control region, and for large-scale deletions. In blood samples from patients, we found a significantly increased number of point mutations compared to the control subjects. In muscle biopsies from 7 of 8 patients whom had received whole body irradiation as well as chemotherapy, the level of a specific mtDNA deletion was significantly greater than in control subjects. Our studies have shown that in patients who have been treated for cancer there is an increased level of mtDNA damage.     

Mitochondrial DNA-deletion mutations accumulate intracellularly to detrimental levels in aged human skeletal muscle fibers

Skeletal muscle-mass loss with age has severe health consequences, yet the molecular basis of the loss remains obscure. Although mitochondrial DNA (mtDNA)-deletion mutations have been shown to accumulate with age, for these aberrant genomes to be physiologically relevant, they must accumulate to high levels intracellularly and be present in a significant number of cells. We examined mtDNA-deletion mutations in vastus lateralis (VL) muscle of human subjects aged 49-93 years, using both histologic and polymerase-chain-reaction (PCR) analyses, to determine the physiological and genomic integrity of mitochondria in aging human muscle. The number of VL muscle fibers exhibiting mitochondrial electron-transport-system (ETS) abnormalities increased from an estimated 6% at age 49 years to 31% at age 92 years. We analyzed the mitochondrial genotype of 48 single ETS-abnormal, cytochrome c oxidase-negative/succinate dehydrogenase-hyperreactive (COX-/SDH++) fibers from normal aging human subjects and identified mtDNA-deletion mutations in all abnormal fibers. Deletion mutations were clonal within a fiber and concomitant to the COX-/SDH++ region. Quantitative PCR analysis of wild-type and deletion-containing mtDNA genomes within ETS-abnormal regions of single fibers demonstrated that these deletion mutations accumulate to detrimental levels (>90% of the total mtDNA).     

The use of temporal temperature gradient gel electrophoresis to reveal mutations in peripheral blood mitochondrial DNA

The mutations in mitochondrial DNA (mtDNA) arise at a higher frequency than in nuclear DNA, and their appearance in peripheral blood can be considered as a sensitive marker to estimate the level of genotoxic load. For revealing the presence of mutations in mtDNA of peripheral blood, we used the method of temporal temperature gradient gel electrophoresis (TTGE). The samples of whole blood DNA from four donor groups were used. Group I contained 10 young (23-26 years) donors and Group II 12 elderly (65-74 years) donors. Group III was formed from patients with breast cancer (12 women) past sessions of radio-chemotherapies (RCHT). Group IV was made of professionals of a nucleus plant occupationally exposed to chronic gamma-irradiation. PCR was carried out on four coding sequences and on one hypervariable sequence of the D-loop (DloopI) of mtDNA. PCR products were tested with TTGE. Most mutations were revealed in the DloopI. Heteroplasmy in the region of DloopI was registered in the blood of each donor of Group III 7 days after the RCHT session. Also, mutations in mtDNA Dloop1 were found in 6 of 13 individuals of Group IV. The blood of this donor group was taken 16 to 28 years after prolonged irradiations in a dose range of 250-350 cGy. In the elderly donor group, the same results were observed in 3 of 12 individuals. The results show that the method of TTGE can be used in mass analyses to assess the effects of radiation and other genotoxic agents in man by detection of unknown mutations in peripheral blood mtDNA.     

Huntington’s Disease and Mitochondrial DNA Deletions: Event or Regular Mechanism for Mutant Huntingtin Protein and CAG Repeats Expansion?!

The mitochondrial DNA (mtDNA) may play an essential role in the pathogenesis of the respiratory chain complex activities in neurodegenerative disorders such as Huntington's disease (HD). Research studies were conducted to determine the possible levels of mitochondrial defect (deletion) in HD patients and consideration of interaction between the expanded Huntingtin gene as a nuclear gene and mitochondria as a cytoplasmic organelle. To determine mtDNA damage, we investigated deletions based in four areas of mitochondrial DNA, in a group of 60 Iranian patients clinically diagnosed with HD and 70 healthy controls. A total of 41 patients out of 60 had CAG expansion (group A). About 19 patients did not show expansion but had the clinical symptoms of HD (group B). MtDNA deletions were classified into four groups according to size; 9 kb, 7.5 kb, 7 kb, and 5 kb. We found one of the four-mtDNA deletions in at least 90% of samples. Multiple deletions have also been observed in 63% of HD patients. None of the normal control (group C) showed mtDNA deletions. The sizes or locations of the deletions did not show a clear correlation with expanded CAG repeat and age in our samples. The study presented evidence that HD patients had higher frequencies of mtDNA deletions in lymphocytes in comparison to the controls. It is thus proposed that CAG repeats instability and mutant Htt are causative factor in mtDNA damage.     

Mitochondrial DNA common deletion is not associated with thyroid, breast and colorectal tumors in Turkish patients

Recently, efforts have been focused on mitochondrial DNA changes and their relation to human cancers. Among them, a 4977 bp deletion of mitochondrial DNA, named "common deletion", has been investigated in several types of tumors, with inconsistent results. In this study, we investigated the presence of the common deletion in tissues from 25 breast, 25 colorectal and 50 thyroid tumors and in the adjacent healthy tissues from Turkish patients. Samples from healthy volunteers were also evaluated for comparison. Two PCR-based methods were used for the detection of the common deletion. First, two pairs of primers were used to amplify wild-type and deleted mtDNA. Then, a highly sensitive nested-PCR was performed, to determine low amounts of deleted genomes. By the first method, wild-type mtDNAs were observed in all samples, but a deletion was observed in only six thyroid samples, by using the nested-PCR method. In conclusion, the mitochondrial common deletion was very rare in our study group and did not appear to be not related with cancer.