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Clinical evaluation and mitochondrial DNA sequence analysis in three Chinese families with Leber's hereditary optic neuropathy.

We report here the clinical, genetic, and molecular characterization of three Chinese families (WZ4, WZ5, and WZ6) with Leber's hereditary optic neuropathy (LHON). Clinical and genetic evaluations revealed the variable severity and age-of-onset in visual impairment in these families. Penetrances of visual impairment in these Chinese families were 33.3%, 35.7%, and 35.5%, respectively, with an average 34.8%. Furthermore, the average age-at-onset in those Chinese families was 17, 20, and 18 years. In addition, the ratios between affected male and female matrilineal relatives in these Chinese families were 3:0, 1:1, and 1.2:1, respectively. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the distinct sets of mtDNA polymorphism, in addition to the identical G11778A mutation associated with LHON in many families. The fact that mtDNA of those pedigrees belonged to different haplogroups F1, D4, and M10 suggested that the G11778A mutation occurred sporadically and multiplied through evolution of the mtDNA in China. However, there was the absence of functionally significant mutations in tRNA and rRNAs or secondary LHON mutations in these Chinese families. The I187T mutation in the ND1, the S99A mutation in the A6, the V254I in CO3, and I58V in ND6 mutation, showing high evolutional conservation, may contribute to the phenotypic expression of the G11778A mutation in the WZ6 pedigree. By contrast, none of mtDNA variants are evolutionarily conserved and implicated to have significantly functional consequence in WZ4 and WZ5 pedigrees. Apparently, these variants do not have a potential modifying role in the development of visual impairment associated with G11778A mutation in those two families. Thus, nuclear modifier gene(s) or environmental factor(s) seem to account for the penetrance and expressivity of LHON in these three Chinese families carrying the G11778A mutation.

Adolescent↗

Clinical evaluation and mitochondrial DNA sequence analysis in two Chinese families with aminoglycoside-induced and non-syndromic hearing loss.

We report here the clinical, genetic, and molecular characterization of two Chinese pedigrees with aminoglycoside-induced and non-syndromic hearing impairment. Clinical evaluation revealed the variable phenotype of hearing impairment including audiometric configuration in these subjects. Penetrances of hearing loss in BJ105 and BJ106 pedigrees are 67% and 33%, respectively. In particular, three of 10 affected matrilineal relatives of BJ105 pedigree had aminoglycoside-induced hearing loss, while seven affected matrilineal relatives in BJ105 pedigree and six affected matrilineal relatives in BJ106 pedigree did not have a history of exposure to aminoglycosides. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the identical homoplasmic A1555G mutation and distinct sets of mtDNA variants belonging to haplogroups F3 and M7b. These variants showed no evolutionary conservation, implying that mitochondrial haplotype may not play a significant role in the phenotypic expression of the A1555G mutation in these Chinese pedigrees. However, aminoglycosides and nuclear backgrounds appear to be major modifier factors for the phenotypic manifestation of the A1555G mutation in these Chinese families.

Aminoglycosides↗

Extremely low penetrance of deafness associated with the mitochondrial 12S rRNA T1095C mutation in three Chinese families.

Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. We report here the clinical, genetic, and molecular characterization of three Chinese pedigrees (a total of 43 matrilineal relatives) with aminoglycoside-induced impairment. Clinical evaluation revealed the variable phenotype of hearing impairment including audiometric configuration in these subjects, although these subjects shared some common features: being bilateral and sensorineural hearing impairment. Strikingly, only probands of these Chinese pedigrees exhibited severe to profound hearing loss. Mutational analysis of the mtDNA in these pedigrees showed the presence of homoplasmic 12S rRNA T1095C mutation, which has been associated with hearing impairment in several families. Sequence analysis of the complete mitochondrial genomes in these pedigrees showed the identical homoplasmic T1095C mutation and distinct sets of mitochondrial DNA (mtDNA) variants belonging to haplogroups M11C. Despite the presence of several highly evolutionarily conservative variants in protein-encoding genes and 16S rRNA gene, the extremely low penetrance of hearing loss with the T1095C mutation implies that the mitochondrial variants may not play an important role in the phenotypic expression of the T1095C mutation in these Chinese families. However, the history of exposure to aminoglycosides in these three hearing-impaired subjects suggested that the aminoglycosides very likely are the cause of hearing loss.

China↗

Mitochondrial DNA G10398A polymorphism imparts maternal Haplogroup N a risk for breast and esophageal cancer.

Mitochondria are the major source of Reactive Oxygen Species (ROS) and mtDNA G10398A (Ala-->Thr) polymorphism, proposed to be involved in increased ROS production, has been shown in association with invasive breast cancer in African-American (AA) women [J.A. Canter, A.R. Kallianpur, F.F. Parl, R.C. Millikan, Mitochondrial DNA G10398A polymorphism and invasive breast cancer in African-American women, Cancer Res. 65 (2005) 8028-8033] and prostate cancer in AA men [M.P. Mims, T.G. Hayes, S. Zheng, S.M. Leal, A. Frolov, M.M. Ittmann, et al., Mitochondrial DNA G10398A polymorphism and invasive breast cancer in African-American women, Cancer Res. 66 (2006) 1880; author reply 1880-1881]. The role of mitochondria, however, in cancer development has been in question recently [A. Salas, Y.G. Yao, V. Macaulay, A. Vega, A. Carracedo, H.J. Bandelt, A critical reassessment of the role of mitochondria in tumorigenesis, PLoS Med. 2 (2005) e296], which has made it pertinent to analyze the data and test the hypotheses by conducting fresh case-control studies. This study, therefore, makes an attempt to validate the exclusive presence of mtG10398A (Ala-->Thr) polymorphism in a haplotype constituting mtDNA haplogroup N and its sublineages, imparting this group a higher risk for breast cancer, based on the re-analyses of approximately 1000 complete human mtDNA sequences worldwide and collated information on 2334 individuals belonging to 18 regions in India. The conclusion drawn of mt10398A allele providing a risk towards cancer is confirmed in a case-control comparison study of 124 sporadic breast cancer patients and 273 controls; and 55 squamous cell carcinoma of esophagus, ESCC, and 163 controls, matched for age, ethnicity and sex from north India. It is further apparent from the study that such a mtDNA polymorphism background provides a higher risk for the cancers of the tissues which could be affected by environmental insults directly as in the ESCC, observed with a high acquired (somatic) rate of mutation in p53 when compared to the breast cancer, suggesting that the mtDNA variants that arose as energetic adaptations, influence our health differentially under different environment conditions and a given genetic background of the mt genome.

Adolescent↗

Novel mutations found in mitochondrial diabetes in Chinese Han population.

Mitochondria provide cells with most of the energy in the form of ATP. Mutations in mitochondrial DNA (mtDNA) are associated with type 2 diabetes mellitus (T2DM) because ATP plays a critical role in the production and the release of insulin. To systematically determine mutant loci and to investigate their association with T2DM in Chinese Han population, 17 commonly reported mutant loci were screened in 236 cases of T2DM and 240 normal controls by PCR-RFLP, allele-specific PCR (AS-PCR) and DNA sequencing methods. Biological softwares were used to analyze the secondary structure of DNA, RNA and the corresponding proteins for missense mutations. Sixteen mutant loci were detected in total, of which five were novel, GenBank accession nos. were DQ092356, DQ473644 and DQ473645; they were mainly in16S rRNA, ND1 and ND4 gene. There was significant difference between the two groups for ND1 and ND4 genes mutation frequencies (ND1: P=0.001, OR=3.944, 95% CI 1.671-9.306; ND4: P=0.010, OR=5.818, 95% CI 1.275-26.537). No significant association was observed between the two groups for 5178A/C polymorphisms (P=0.418). Our study suggested that T3394C and A12026G might be associated with T2DM in Chinese Han population, and T2DM with mtDNA variant should be considered mitochondrial diabetes.

Adult↗

Frontotemporal dementia and mitochondrial DNA transitions.

Frontotemporal dementia (FTD) is the second most common type of primary degenerative dementia. Some patients present an overlap between Alzheimer's disease (AD) and FTD both in neuropathological and clinical aspects. This may suggest a similar overlap in physiopathology, namely an involvement of mitochondrial DNA (mtDNA) in FTD, as it has been associated to AD. To determine if mtDNA is involved in FTD, we performed a Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) analysis, specific to mtDNA NADH Dehydrogenase subunit 1 (ND1) nucleotides 3337-3340, searching for mutations previously described in Parkinson's and AD patients. We could identify one FTD patient with two mtDNA transitions: one already known (3316 G-to-A) and another unreported (3337 G-to-A). Additionally, mitochondrial respiratory chain complex I activity was reduced in leukocytes of this patient (36% of the control mean activity). To our knowledge, this is the first report of mtDNA variants in FTD patients.

Aged↗

Ancient mitochondrial M haplogroups identified in the Southwest Pacific.

Based on whole mtDNA sequencing of 14 samples from Northern Island Melanesia, we characterize three formerly unresolved branches of macrohaplogroup M that we call haplogroups M27, M28, and M29. Our 1,399 mtDNA control region sequences and a literature search indicate these haplogroups have extremely limited geographical distributions. Their coding region variation suggests diversification times older than the estimated date for the initial settlement of Northern Island Melanesia. This finding indicates that they were among the earliest mtDNA variants to appear in these islands or in the ancient continent of Sahul. These haplogroups from Northern Island Melanesia extend the existing schema for macrohaplogroup M, with many independent branches distributed across Asia, East Africa, Australia, and Near Oceania.

Ancient Lands↗

Evidence for non-neutrality of mitochondrial DNA haplotypes in Drosophila pseudoobscura.

Mitochondrial DNA (mtDNA) haplotypes usually are assumed to be neutral, unselected markers of evolving female lineages. This assumption was tested by monitoring haplotype frequencies in 12 experimental populations of Drosophila pseudoobscura which were polymorphic for mtDNA haplotypes. Populations were maintained for at least 10 generations, and in one case for 32 generations, while tests of mtDNA selective neutrality were conducted. In an initial population, formed from a mixture of two strains with different mitochondrial haplotypes, the frequency of the Bogota haplotype increased 46% in 3 generations, reaching an apparent equilibrium frequency of 82% after 32 generations. Perturbation of this equilibrium by addition of the less common haplotype resulted in a rapid, dramatic increase in frequency of the second haplotype, and a return to essentially the same equilibrium frequency as before perturbation. This behavior is not consistent with mtDNA neutrality, nor is the equilibrium consistent with a simple model of constant selection on the haploid mtDNAs. Replicate cage experiments with mtDNA haplotypes did not always generate the same result as the initial cage. Several lines of evidence, including manipulations of the nuclear genome, support the idea that both nuclear and mitochondrial genomes are involved in the dramatic mtDNA frequency changes. In another experiment, strong female viability selection was implicated via mtDNA frequency changes. Although the causes of the dramatic mtDNA frequency changes in our populations are not obvious, it is clear that Drosophila mitochondrial haplotypes are not always simply neutral markers. Our findings are relevant to the introduction of a novel mtDNA variant from one species or one population into another. Such introductions could be strongly favored by selection, even if it is sporadic.

Animals↗

Cytoplasmic incompatibility in Drosophila simulans: dynamics and parameter estimates from natural populations.

In Drosophila simulans, cytoplasmically transmitted Wolbachia microbes cause reduced egg hatch when infected males mate with uninfected females. A Wolbachia infection and an associated mtDNA variant have spread northward through California since 1986. PCR assays show that Wolbachia infection is prevalent throughout the continental US and Central and South America, but some lines from Florida and Ecuador that are PCR-positive for Wolbachia do not cause incompatibility. We estimate from natural populations infection frequencies and the transmission and incompatibility parameter values that affect the spread of the infection. On average, infected females from nature produce 3-4% uninfected ova. Infected females with relatively low fidelity of maternal transmission show partial incompatibility with very young infected laboratory males. Nevertheless, crosses between infected flies in nature produce egg-hatch rates indistinguishable from those produced by crosses between uninfected individuals. Incompatible crosses in nature produce hatch rates 30-70% as high as those from compatible crosses. Wild-caught infected and uninfected females are equally fecund in the laboratory. Incompatibility decreases with male age, and age-specific incompatibility levels suggest that males mating in nature may often be 2 or 3 weeks old. Our parameter estimates accurately predict the frequency of Wolbachia infection in California populations.

Africa, Southern↗

Update of the Human MitBASE database.

Human MitBASE is a database collecting human mtDNA variants. This database is part of a greater mitochondrial genome database (MitBASE) funded within the EU Biotech Program. The present paper reports the recent improvements in data structure, data quality and data quantity. As far as the database structure is concerned it is now fully designed and implemented. Based on the previously described structure some changes have been made to optimise both data input and data quality. Cross-references with other bio-databases (EMBL, OMIM, MEDLINE) have been implemented. Human MitBASE data can be queried with the MitBASE Simple Query System (http://www.ebi.ac.uk/htbin/Mitbase/mit base.pl) and with SRS at the EBI under the 'Mutation' section (http://srs.ebi.ac.uk/srs5/). At present the HumanMitBASE node contains approximately 5000 variants related to studies investigating population polymorphisms and pathologies.

Animals↗

Mitochondrial DNA loss caused by ethanol in Saccharomyces flor yeasts.

Saccharomyces flor yeasts proliferate at the surface of sherry wine, which contains over 15% (vol) ethanol. Since ethanol is a powerful inducer of respiration-deficient mutants, this alcohol has been proposed to be the source of the high diversity found in the mitochondrial genomes of flor yeasts and other wine yeasts. Southern blot analysis suggests that mitochondrial DNA (mtDNA) polymorphic changes are due to minor lesions in the mitochondrial genome. As determined in this work by pulsed-field gel electrophoresis, restriction analysis, and Southern blot analysis, ethanol-induced petite mutants completely lack mtDNA (rho zero). Ethanol-induced changes in the mitochondrial genome that could explain the observed mtDNA polymorphism in flor yeasts were not found. The transfer of two different mtDNA variants from flor yeasts to a laboratory strain conferred in both cases an increase in ethanol tolerance in the recipient strain, suggesting that mtDNAs are probably subjected to positive selection pressure concerning their ability to confer ethanol tolerance.

DNA Damage↗

A mitochondrial paradigm of metabolic and degenerative diseases, aging, and cancer: a dawn for evolutionary medicine.

Life is the interplay between structure and energy, yet the role of energy deficiency in human disease has been poorly explored by modern medicine. Since the mitochondria use oxidative phosphorylation (OXPHOS) to convert dietary calories into usable energy, generating reactive oxygen species (ROS) as a toxic by-product, I hypothesize that mitochondrial dysfunction plays a central role in a wide range of age-related disorders and various forms of cancer. Because mitochondrial DNA (mtDNA) is present in thousands of copies per cell and encodes essential genes for energy production, I propose that the delayed-onset and progressive course of the age-related diseases results from the accumulation of somatic mutations in the mtDNAs of post-mitotic tissues. The tissue-specific manifestations of these diseases may result from the varying energetic roles and needs of the different tissues. The variation in the individual and regional predisposition to degenerative diseases and cancer may result from the interaction of modern dietary caloric intake and ancient mitochondrial genetic polymorphisms. Therefore the mitochondria provide a direct link between our environment and our genes and the mtDNA variants that permitted our forbears to energetically adapt to their ancestral homes are influencing our health today.

Aging↗

Clinical applications of denaturing high-performance liquid chromatography-based genotyping.

AIM: To develop and evaluate heteroduplex forming templates (HFTs) as a common set of molecular standards for genotyping by denaturing high-performance liquid chromatography (DHPLC) using hypervariable regions of human mitochondrial DNA (mtDNA) as a model system. METHODS: Hypervariable regions 1 and 2 from the mtDNA D-loop of 22 maternally related and unrelated human volunteers were amplified by polymerase chain reaction (PCR) and individually mixed with each of three HFTs. Following denaturation and reannealing of the mixture, the resulting hetero- and homoduplicies were separated by DHPLC using temperature-modulated heteroduplex analysis. RESULTS: Each of three HFTs, when cross-hybridized with a target mtDNA amplicon, induced the formation of an assemblage hetero- and homoduplex peaks, which were uniquely characteristic of a given mtDNA sequence variant. The mtDNA DHPLC profiles obtained in the current study were identical between maternal relatives and different between unrelated individuals--consistent with uniparental maternal inheritance of mtDNA in humans. CONCLUSION: DHPLC in combination with a common set of HFTs targeted to a locus of interest can be used as a reliable means of genotyping. DHPLC profiles can be readily stored as a bit-coded string of hetero- and homoduplex peak retention times to form a searchable database. This approach to DHPLC genotyping will have immediate utility in extended pedigree analyses, where it will allow rapid sorting and/or confirmation of maternal lineages. Additional applications of DHPLC profiling include the discovery and scoring of clinically relevant nuclear and mitochondrial loci.

Chromatography, High Pressure Liquid↗

[Search for mitochondrial DNA T4291C mutation in Hungarian patients with metabolic syndrome].

INTRODUCTION: Metabolic syndrome affects 15-30 percentage of the population. It is characterized by obesity, hypertension, diabetes mellitus, insulin resistance, hypercholesterolemia and hypertriglyceridemia. AIMS: In a recent study metabolic syndrome was shown to be transmitted on maternal lineage in a large family; an uridine to cytidine transition was detected in homoplasmic form at position 4291 of the mitochondrial DNA (mtDNA) which affects the 5' neighboring nucleotide to the anticodon of the isoleucine-tRNA. METHODS: Using specific restriction analysis and direct sequencing for detection of this mutation the authors genotyped 365 DNA samples which were collected from 164 adult and 119 pediatric patients with metabolic syndrome. RESULTS AND CONCLUSIONS: The T4291C mtDNA variant could not be detected in any of these patients suggesting that this alteration is likely rare in the Hungarian metabolic syndrome population.

Adolescent↗

Association of mitochondrial deoxyribonucleic acid 16189 variant (T->C transition) with metabolic syndrome in Chinese adults.

OBJECTIVE: A common variant in mitochondrial DNA (mtDNA) at bp 16189 (T-->C transition) has been associated with small birth size, adulthood hyperglycemia, and insulin resistance in Caucasians. In this study, we investigated whether mtDNA 16189 variant is associated with metabolic syndrome in Chinese subjects. METHODS: Six hundred fifteen Chinese adults, aged 40 yr or older, were recruited in this study. The 16189 variant of mtDNA was detected using PCR and restriction enzyme digestion. Metabolic syndrome was diagnosed on modified National Cholesterol Education Program Adult Treatment Panel III guidelines, using body mass index (BMI) instead of waist circumference. An association study was performed with chi2 test and logistic regression analysis. RESULTS: The prevalence of the 16189 variant was higher in patients with metabolic syndrome than in those without: 44% (125 of 284) vs. 33.2% (110 of 331) (P = 0.006). The association between this 16189 variant of mtDNA and metabolic syndrome (P = 0.021) remained significant even after correcting for age and BMI. As to the individual traits, the prevalence of fasting plasma glucose of at least 110 mg/dl (> or =6.1 mmol/liter) [(51.5% (121 of 235) vs. 42.1% (160 of 380); P = 0.023], type 2 diabetes mellitus [48.1% (113 of 235) vs. 39.2% (149 of 380); P = 0.031], and hypertriglyceridemia [44.3% (104 of 235) vs. 35.8% (136 of 380); P = 0.037] were significantly higher in subjects harboring the 16189 variant of mtDNA than those with the wild type. However, the prevalence of hypertension [53.2% (125 of 235) vs. 47.6% (181 of 380); P = 0.180], BMI greater than 25 kg/m2 [48.5% (114 of 235) vs. 43.9% (167 of 380); P = 0.270], and low high-density lipoprotein cholesterol [61.3% (144 of 235) vs. 54.7% (208 of 380); P = 0.111] did not reach a significant difference between the two groups. Furthermore, there was a trend of increasing frequency of occurrence of the 16189 variant in individuals having an increasing number of components of metabolic syndrome (Ptrend < 0.005). CONCLUSION: Our data strongly suggest that mtDNA 16189 variant underlies susceptibility to metabolic syndrome in the Chinese population.

Aged↗

Maternal inheritance in cyclic vomiting syndrome with neuromuscular disease.

Cyclic vomiting syndrome (CVS), characterized by severe discrete episodes of nausea, vomiting, and lethargy, is a predominately childhood condition associated with migraine and dysautonomic features. Disease-associated mitochondrial DNA (mtDNA) sequence variants are suggested by a strong maternal bias in the inheritance of migraine, and the recent findings of mtDNA variants in a few children with CVS and additional neuromuscular disease manifestations ("CVS+"). A clinical interview using a questionnaire was administered (generally) to one parent of 62 children with CVS+. Non-senile disease manifestations, including migraine, myopathy, seizures, and dysautonomia-like symptoms, were far more common in matrilineal versus non-matrilineal relatives, including being present in 75% of the mothers versus in only 11% of the fathers (P < 0.001). Overall, maternal inheritance is suggested in 86% of the families (in 65% strongly so). Disease manifestations in subjects and their affected matrilineal relatives are predominately intermittent and consistent with dysautonomia, including increased vital sign fluctuations. Body fluid metabolites and muscle biopsy findings are consistent with mitochondrial dysfunction in most cases tested. We conclude that mtDNA sequence variants are at least risk factors in the development of disease in most children at this "severe" end of the CVS spectrum, likely involving a maternally inherited propensity towards dysautonomia.

Antidepressive Agents, Tricyclic↗

Mitochondrial DNA involvement in human longevity.

The main message of this review can be summarized as follows: aging and longevity, as complex traits having a significant genetic component, likely depend on a number of nuclear gene variants interacting with mtDNA variability both inherited and somatic. We reviewed the data available in the literature with particular attention to human longevity, and argued that what we hypothesize for aging and longevity could have a more general relevance and be extended to other age-related complex traits such as Alzheimer's and Parkinson's diseases. The genetics which emerges for complex traits, including aging and longevity, is thus even more complicated than previously thought, as epistatic interactions between nuclear gene polymorphisms and mtDNA variability (both somatic and inherited) as well as between mtDNA somatic mutations (tissue specific) and mtDNA inherited variants (haplogroups and sub-haplogroups) must be considered as additional players capable of explaining a part of the aging and longevity phenotype. To test this hypothesis is one of the main challenge in the genetics of aging and longevity in the next future.

Cell Nucleus↗

Genetic variants of Complex I in multiple sclerosis.

HYPOTHESIS: A mitochondrial mechanism contributes to neurodegeneration in multiple sclerosis (MS). Genetic variants of Complex I genes may influence the nature of tissue response to inflammation in the central nervous system (CNS). BACKGROUND: Complex I is encoded by seven mitochondrial and 38 nuclear genes. Many of the nuclear genes colocalize with regions where full genome scans detected linkage in MS. Previous studies revealed an association between variants of mitochondrial (mt)DNA encoded subunits of Complex I and MS. Biochemical studies suggested a functional involvement of Complex I in the degenerative processes downstream to inflammatory injury in the CNS. METHODS: Patients with all MS phenotypes were included. DNA specimens of affected sib pair, trio and multiplex families were studied. Single nucleotide polymorphisms (SNP) were determined by using the Taqman assay. The association of MS with nuclear DNA encoded alleles and haplotypes of Complex I was tested by the pedigree disequilibrium test (PDT) and by the transmit program in the families. Haplotypes were further investigated by using ldmax (GOLD). The association of mtDNA encoded variants with MS was tested by the Fisher's Exact Test. RESULTS: The previously identified MS-associated mtDNA variants and haplotypes were not increased in mothers as compared to fathers in these families. However, an association of all clinical phenotypes with haplotypes within NDUFS5 (1p34.2-p33), NDUFS7 (19p13) and NDUFA7 (19p13) was detected. The inclusion of families with primary progressive (PP)-MS phenotype did not modify the outcome and, as a subgroup alone, did not have a sufficient size to draw conclusion regarding phenotype specific associations. CONCLUSIONS: SNP haplotypes within Complex I genes are associated with MS. Further studies are needed to refine the identification of disease relevant variants nearby or within these haplotypes. Molecular and functional properties of Complex I subunits may offer novel explanations to better understand the relationship between inflammation and neurodegeneration.

Alleles↗