Mitochondrial tRNALeu/Lys and ATPase 6/8 gene variations in spinocerebellar ataxias.

BACKGROUND: The spinocerebellar ataxias (SCA) comprise a heterogeneous group of severe late-onset neurodegenerative diseases that are promoted by the expansion of a tandem-arrayed DNA sequence that modifies the primary structure of the protein. METHODS: Genomic DNA of 20 patients affected with SCAs was extracted from peripheral blood and screened for deletions in mitochondrial DNA (mtDNA). Sequencing of tRNA(Leu), tRNA(Lys), cytochrome oxidase II, ATPase 6/8 and NADH dehydrogenase I (NDI) genes belonging to mtDNA from patients with SCAs was also carried out to detect the presence of variations. RESULTS: We identified cytosine-adenine-guanine (CAG) trinucleotide repeat expansions in 20 patients. Seven of these patients had at least one nucleotide change in mtDNA. In such cases, 5 nucleotide variations resulted in amino acid changes with two novel variations T8256G and G9010A. CONCLUSION: SCA patients showed high levels of mtDNA variations in lymphocytes. It can be proposed that the SCA gene proteins (Ataxins) are involved in the complicated intracellular mechanisms that affect cellular organelles and their components, such as the mitochondrial genome. The instability of CAG repeats in polyglutamine diseases such as SCAs and Huntington's disease might be a causative factor in mtDNA variation or possible damage.

Investigation of tRNA(Leu/Lys) and ATPase 6 genes mutations in Huntington's disease.

Huntington disease (HD) is a genetically dominant condition caused by expanded CAG repeats which code for glutamine in the HD gene product, huntingtin. Huntingtin is expressed in almost all tissues, so abnormalities outside the brain can also be expected. Involvement of nuclei and mitochondria in HD pathophysiology has been suggested. In fact mitochondrial dysfunction is reported in brains of patients suffering from HD. The tRNA gene mutations are one of hot spots that can cause mitochondrial disorders. In this study, possible mitochondrial DNA (mtDNA) damage was evaluated by screening for mutations in the tRNA(leu/lys) and ATPase 6 genes of 20 patients with HD, using PCR and automated DNA sequencing. Mutations including an A8656G mutation in one patient were observed, which may be causal to the disease. Understanding the role of mitochondria in the pathogenesis of neurodegenerative diseases could potentially be important for the development of therapeutic strategies in HD.

Use of D11S2179 and D11S1343 as markers for prenatal diagnosis of ataxia telangiectasia in Iranian patients.

Ataxia telangiectasia (AT) is an autosomal recessive disorder with an estimated prevalence of 1/40,000 to 1/100,000 in reported populations. There is a 25% possibility for having an affected child when parents are carriers for the ATM gene mutation. There is no cure available for this disease and prenatal testing is strongly recommended for prevention of this disease. Although the preferred method is the direct mutation analysis of the ATM gene, the large size of the ATM gene with 63 exons and the large number of possible mutations in patients considerably limit efficiency of mutation analysis as a diagnostic choice. Indirect method is a better tool when parents are not carriers of founder mutation and pass different mutations to their children. Indirect molecular diagnosis using ATM-related molecular markers facilitates prenatal diagnosis of AT children. In this study, four molecular markers: D11S2179, D11S1787, D11S535, D11S1343 are genotyped in 19 unrelated families from different regions of Iran. Those markers are amplified using extracted sequence primers from the Gene Bank with their described PCR conditions. Amplified products were separated using denaturing PAGE gels, and data were analyzed to detect their pattern of inheritance in each family. In all families, segregation of alleles was according to Mendelian inheritance, and affected chromosomes were distinguishable from unaffected ones. All carriers and affected patients were diagnosed accurately. Thus, this method is effectively useful in prenatal diagnosis of AT.

Identification and sizing of GAA trinucleotide repeat expansion, investigation for D-loop variations and mitochondrial deletions in Iranian patients with Friedreich's ataxia.

Friedreich's Ataxia (FA) is the commonest genetic cause of ataxia and is associated with the expansion of a GAA repeat in intron 1 of the frataxin gene. Iron accumulation in the mitochondria of patients with FA would result in hypersensitivity to oxidative stress. Mitochondrial DNA (mtDNA) could be considered a candidate modifier factor for FA disease, since mitochondrial oxidative stress is thought to be involved in the pathogenesis of this disease. We studied 25 Iranian patients (16 females and 9 males) from 12 unrelated families. DNA from each patient was extracted and frequency and length of (GAA)(n) repeat was analyzed using a long-range polymerase chain reaction (PCR) test. Also we investigated impact of GAA size on neurological findings, age of onset and disease development. In order to identify polymorphic sites and genetic background, the sequence of two hypervariable regions (HVR-I and HVR-II) of mtDNA was obtained from FA patients harbouring GAA trinucletide expansions. Alignment was made with the revised cambridge reference sequence (rCRS) and any differences recorded as single base substitution (SBS), insertions and deletions. Homozygous GAA expansion was found in 21 (84%) of all cases. In four cases (16%), no expansion was observed, ruling out the diagnosis of Friedreich's ataxia. In cases with GAA expansions, ataxia, scoliosis and pes cavus, cardiac abnormalities and some neurological findings occurred more frequently than in our patients without GAA expansion. Molecular analysis was imperative for diagnosis of Friedreich's ataxia, not only for typical cases, but also for atypical ones. Diagnosis bases only on clinical findings is limited, however, it aids in better screening for suspected cases that should be tested. Our results showed that the rate of D-loop variations was higher in FA patients than control (P<0.05). mtDNA deletions were present in 76% of our patients representing mtDNA damage, which may be due to iron accumulation in mitochondria.

Tumoral cell mtDNA approximately 8.9 kb deletion is more common than other deletions in gastric cancer.

BACKGROUND: The aim of the study was to clarify the role of deletion of mitochondrial DNA (mtDNA) in gastric carcinogenesis and to determine prevalence of mitochondrial deletions in different regions of tumoral tissue in comparison with adjacent non-tumoral tissue in gastric cancer. METHODS: In order to investigate whether a high incidence of mutations exists in mtDNA of gastric cancer tissues, we screened five regions of the mitochondrial genome by PCR amplification, Southern blot and DNA sequence analysis. RESULTS: Of 71 cancer patients, the approximately 8.9 kb deletion was detected among different deletions in 9 cases (12.67%) of the tumoral tissues and 1 case (1.40%) in non-tumoral tissues that were adjacent to the tumors. Level of the 8.9 kb deletion has been found to be more than other deletions in tumoral tissues. CONCLUSIONS: The approximately 8.9 kb deletion has an obvious correlation with age and histological type. These data suggest that the approximately 8.9 kb deletion in mtDNA may play an important role in gastric carcinogenesis.

Delta mtDNA4977 is more common in non-tumoral cells from gastric cancer sample.

BACKGROUND: The aim of this study was to determine the frequency of delta mtDNA4977 in tumoral cells as compared with adjacent normal cells in gastric cancer. METHODS: In order to investigate whether a high incidence of mutation exists in mitochondrial DNA of gastric cancer tissues, we screened one of common region of the mitochondrial genome by PCR amplification and Southern blot followed by DNA sequence analysis. DNA isolated from these cells was used to amplify hypervariable regions ATPase8/6, COXIII, ND3, ND4 and ND5 of delta mtDNA4977. RESULTS: In 107 cancer patients, delta mtDNA4977 was detected in 6 cases (5.60%) of the tumoral tissues and 18 cases (16.82%) of the non-tumoral tissues that were adjacent to the tumors. Levels of delta mtDNA4977 deletions were found to be more in non-tumoral tissues than in adjacent tumoral tissues. There was no correlation of patients with certain clinical parameters like age, sex, tumor location and tumor size; however, there was an obvious relationship with intestinal-type of gastric cancer. CONCLUSIONS: Unknown genetic aspects, ambiguous environmental factors and reactive oxygen species (ROS) can cause the delta mtDNA4977 mutation rate to be increased in gastric cancer. The results suggest that percentage level of delta mtDNA4977 is less common and intolerable in tumoral tissue, probably because of high metabolism and ROS generation. We supposed that the cells initially had delta mtDNA4977 transform to tumoral cells and the existed deletion conferred metabolic disadvantage; thus, cells containing such a mtDNA deletion would be overgrown by other cancer cells without this mtDNA deletion. As a result, the presence of delta mtDNA4977 will be low in tumoral cells.

Investigation on mitochondrial tRNA(Leu/Lys), NDI and ATPase 6/8 in Iranian multiple sclerosis patients.

As with chromosomal DNA, the mitochondrial DNA (mtDNA) can contain mutations that are highly pathogenic . In fact, many diseases of the central nervous system are known to be caused by mutations in mtDNA. Dysfunction of the mitochondrial Respiratory Chain (RC) has been shown in patients with neurological disease including Alzheimer's disease (AD), Parkinson's disease (PD) and Multiple sclerosis (MS). MS is a demyelinating disease of central nervous system characterized by morphological hallmarks of inflammation, demyelination and axonal loss. Considering this importance, we decided to investigate several highly mutative parts of mtDNA for point mutations as MT-LTI (tRNA(Leucine1(UUA/G))), MT-NDI (NADH Dehydrogenase subunit 1), MT-COII (Cytochrome c oxidase subunit II), MT-TK (tRNA(Lysine)), MT-ATP8 (ATP synthase subunit F0 8) and MT-ATP6 (ATP synthase subunit F0 6) in 20 Iranian MS patients and 80 age-matched control subjects by PCR and automated DNA sequencing to evaluate any probable point mutations. Our results revealed that 15 (75%) out of 20 MS patients had point mutations. Some of point mutations were newly found in this study. This study suggested that point mutation occurred in mtDNA might be involved in pathogenesis of MS.

Do haplogroups H and U act to increase the penetrance of Alzheimer's disease?

1. Alzheimer's disease (AD) is the most common form of dementia in the elderly in which interplay between genes and the environment is supposed to be involved. Mitochondrial DNA (mtDNA) has the only noncoding regions at the displacement loop (D-loop) region that contains two hypervariable segments (HVS-I and HVS-II) with high polymorphism. mtDNA has already been fully sequenced and many subsequent publications have shown polymorphic sites, haplogroups, and haplotypes. Haplogroups could have important implications to understand the association between mutability of the mitochondrial genome and the disease.2. To assess the relationship between mtDNA haplogroup and AD, we sequenced the mtDNA HVS-I in 30 AD patients and 100 control subjects. We could find that haplogroups H and U are significantly more abundant in AD patients (P = 0.016 for haplogroup H and P = 0.0003 for haplogroup U), Thus, these two haplogroups might act synergistically to increase the penetrance of AD disease.

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.

Do mitochondrial DNA haplogroups play a role in susceptibility to tuberculosis?

BACKGROUND AND OBJECTIVES: Mitochondrial DNA has a unique role in ATP production and subsequent mitochondrial reactive oxygen species (ROS) production in eukaryotic cells and there is a potential role for ROS and oxygen burst against Mycobacterium tuberculosis, an intracellular pathogen. This study aimed to determine whether the frequency of different mitochondrial haplogroups was significantly different in patients with tuberculosis (TB) compared with a normal population. METHODS: Mitochondrial DNA haplogroups M, N, J and K were studied by PCR-restriction fragment length polymorphism and sequencing. Cases were 54 patients with confirmed smear positive pulmonary TB. Controls were 256 healthy persons. RESULTS: There were no statistically significant differences between those with TB and the control group. CONCLUSIONS: There was no statistically significant association between mtDNA haplogroups and the presence of TB infection.

Mitochondrial D-loop variation in Persian multiple sclerosis patients: K and A haplogroups as a risk factor!!

: Multiple Sclerosis (MS) is a multifocal demyelinating central nervous system disorder in which interplay between genes and the environment are supposed to be involved. Mitochondrial DNA (mtDNA) has the only non-coding regions at the displacement loop (D-loop) region that contains two hypervariable segments (HVS-I and HVS-II) with high polymorphism. mtDNA has already been fully sequenced and many subsequent publications have showed polymorphic sites, haplogroups and haplotypes. Haplogroups could have important implications to understand association between mutability of the mitochondrial genome and disease. To assess relationship between mtDNA haplogroups and MS, we have sequenced the mtDNA HVS-I in 54 MS patients and 100 control subjects. We have found that haplogroups A and K are significantly more abundant in MS patients (P=0.042 for haplogroup A and P=0.0005 for haplogroup K). Thus, these two haplogroups might act synergistically to increase the penetrance of MS disease.