Mutations of the mitochondrial ND1 gene as a cause of MELAS.
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Adolescent↗
Biomedical subjects
R W Taylor
Publications and source records attributed to R W Taylor.
No association of the mitochondrial DNA A12308G polymorphism with increased risk of stroke in patients with the A3243G mutation.
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DNA Mutational Analysis↗
Late-onset encephalopathy associated with a C11777A mutation of mitochondrial DNA.
A 67-year-old man presented with cognitive deficits, status epilepticus, left hemiparesis, and severe lactic acidosis. Respiratory chain enzyme analysis of skeletal muscle revealed a defect in complex I activity, associated with a heteroplasmic C11777A mutation in the mitochondrial ND4 gene. This case is remarkable not only because of the late onset of symptoms, but because this mutation affects the identical ND4 codon as the G11778A mutation that causes Leber hereditary optic neuropathy.
Acidosis, Lactic↗
Mutations of ANT1, Twinkle, and POLG1 in sporadic progressive external ophthalmoplegia (PEO).
To verify the impact of mutations in ANT1, Twinkle, and POLG1 genes in sporadic progressive external ophthalmoplegia associated with multiple mitochondrial DNA (mtDNA) deletions, DNA samples from 15 Italian and 12 British patients were screened. Mutations in ANT1 were found in one patient, in Twinkle in two patients, and in POLG1 in seven patients. Irrespective of the inheritance mode, screening of these genes should be performed in all patients with progressive external ophthalmoplegia with multiple mtDNA deletions.
Adenine Nucleotide Translocator 1↗
Investigation of mitochondrial function in hereditary spastic paraparesis.
Following the association of hereditary spastic paraparesis (HSP) with mutation in the paraplegin gene (SPG7) and mitochondrial dysfunction, we wished to investigate whether mitochondrial dysfunction might be associated with other forms of HSP. Five cases of HSP caused by mutation in the spastin gene (SPG4) and nine cases with HSP with mutation in the spastin and paraplegin genes excluded (non-SPG4/SPG7), were investigated for mitochondrial dysfunction. Muscle tissue from the HSP groups and a control group was analysed histochemically and spectrophotometrically for mitochondrial dysfunction. A significant decrease in mitochondrial respiratory chain complexes I and IV was demonstrated in the non-SPG4/SPG7 group. No abnormality was detected in the SPG4 group. We therefore conclude that there is evidence for mitochondrial dysfunction in non-SPG4/SPG7 HSP. There is no evidence for mitochondrial dysfunction in the pathogenesis of spastin-related HSP.
ATPases Associated with Diverse Cellular Activitie↗
Dynamic and static tests of balance and postural sway in boys: effects of previous wrist bone fractures and high adiposity.
Ninety-three males aged 10-21 years undertook the Bruininks-Oseretsky balance test and two computerized posturography tests to evaluate the effects of (a) previous forearm fracture and (b) high body weight on balance and postural sway. Body composition was measured by dual energy X-ray absorptiometry. Fracture history did not affect balance measures. However, Bruininks-Oseretsky balance scores were negatively correlated with body weight, body mass index, percentage fat and total fat mass. Overweight subjects (n=25) had lower scores (P<0.05) than boys of healthy weight (n=47), supporting the view that overweight adolescents have poorer balance than those of healthy weight.
Absorptiometry, Photon↗
Identifying adolescents with high percentage body fat: a comparison of BMI cutoffs using age and stage of pubertal development compared with BMI cutoffs using age alone.
OBJECTIVE: To ascertain whether body mass index (BMI) cutoffs calculated according to age and pubertal stage are superior to BMI cutoffs calculated on the basis of age alone at correctly identifying children and adolescents with high levels of adiposity. DESIGN: Cross-sectional study. SETTING: Dunedin, a university city in New Zealand. SUBJECTS AND MEASUREMENTS: In total, 368 healthy Caucasian children and adolescents (179 males, 189 females) aged 8.5-15.5 y had their percentage body fat measured by dual-energy X-ray absorptiometry (DXA). High adiposity was defined as > or =25% body fat in males and > or =35% body fat in females. The sensitivity, specificity and areas under the receiver operating characteristic curves of two Z-score distributions of BMI were calculated for each gender. RESULTS: Forty-nine males (27.3%) and 43 females (22.8%) had high DXA-measured percentage body fat. In all, 86% of males and females with high adiposity were correctly identified by BMI cutoffs calculated according to age alone, with 89% of males and 97% of females with low adiposity being correctly classified. Similar results were observed when BMI cutoffs utilising both age and stage of pubertal development were used; 90% of males and 88% of females with high adiposity and 92% of both males and females with low adiposity were correctly classified according to BMI. CONCLUSIONS: Categorisation of BMI according to both age and pubertal stage of development does not produce cutoffs that are superior to BMI cutoffs calculated on the basis of age alone at identifying children with high DXA-measured adiposity. SPONSORSHIP: University of Otago and the Health Research Council, New Zealand.
Absorptiometry, Photon↗
Body composition of 4- and 5-year-old New Zealand girls: a DXA study of initial adiposity and subsequent 4-year fat change.
BACKGROUND: Dual-energy X-ray information (DXA) quantitating body fat mass and percentage fat in healthy children of preschool age is scarce. OBJECTIVE: To study the initial variability in body composition and subsequent longitudinal changes in absolute fat mass (kg) and relative adiposity (fat percentage) in a sample of contemporary young New Zealand girls. DESIGN: Cross-sectional study with a longitudinal component. SETTING: University research unit. SUBJECTS: A total of 89 Caucasian girls aged 4-5 y were recruited by advertisement at baseline and 4-y changes in body composition were evaluated in 23 of these girls. METHODS: Total body composition was measured by DXA, height and weight by anthropometry. RESULTS: Baseline values for fat mass varied more than values for lean mass or bone mass. Girls from the upper third of our fat percentage distribution (% fat >19.2%) had more than twice the fat mass (5.34 vs 2.31 kg, P<0.001) of those from the lowest third (% fat &<15.4%). The percentage gain in fat mass over 4 y (124 (95% CI 90-163) also exceeded the percentage gain of lean mass (55 (95% CI 51-59). In data adjusted for age and height, 63.5% of the variance in percentage body fat at time 2 was explained by fat mass at time one. CONCLUSIONS: In girls, the trajectory of fat gain appears to be established at a young age. Our results support the view that body fatness tracks strongly before puberty. Since preventing the accumulation of excessive fat is preferable to reduction of existing excessive fat stores, it is important to put in place strategies to limit excessive fat gain early in life.
Absorptiometry, Photon↗
Somatic mitochondrial DNA mutations in adult-onset leukaemia.
Mitochondrial genome instability has recently been demonstrated in a wide variety of human tumours and is implicated in the development of the myelodysplastic syndromes, a heterogeneous group of haematological disorders with an increased risk of malignant transformation. We therefore investigated the incidence of somatic mitochondrial DNA (mtDNA) mutations in patients with adult-onset leukaemia. We sequenced the entire mitochondrial genome from both normal tissue (buccal epithelial cells) and the leukaemia from 24 patients with adult-onset leukaemia. Somatic mtDNA mutation was present in nine individuals ( approximately 40%) and in each case the tumour genome differed from the normal genome sequence by a single sequence change. Using PCR-RFLP analysis and real-time PCR, we have studied in detail the mutation present in one patient with acute lymphatic leukaemia, demonstrating that the mutation is associated specifically with the leukaemia.
Adolescent↗
Frequency of rare mitochondrial DNA mutations in patients with suspected Leber's hereditary optic neuropathy.
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DNA Mutational Analysis↗
Molecular and functional effects of the T14709C point mutation in the mitochondrial DNA of a patient with maternally inherited diabetes and deafness.
A heteroplasmic T to C transition at nucleotide position 14709 in the mitochondrial tRNA glutamic acid (tRNA(Glu)) gene has previously been associated with maternally inherited diabetes and deafness (MIDD). To investigate the pathogenic mechanism of the T14709C mutation, we have constructed transmitochondrial cell lines by transferring fibroblasts mitochondria from a patient with the mutation into human cells lacking mitochondrial DNA (mtDNA) (rho degrees cells). Clonal cybrid cell lines were obtained containing various levels of the heteroplasmic mutation, or exclusively mutated or wild-type mtDNA. Measurement of respiratory chain enzymatic activities failed to detect a difference between the homoplasmic mutant and homoplasmic wild-type cybrid cell lines. However, a subtle decrease in the steady-state levels of tRNA(Glu) transcripts in some mutant clones. Our studies suggest that the T14709C mutation is insufficient to lead impairment of mitochondrial function in homoplasmic osteosarcoma cybrid clones, and that we cannot exclude that the T14709C mutation affects mitochondrial function by a yet unidentified mechanism.
Base Sequence↗
Spinal overload: a concern for obese children and adolescents?
Heavy children require stronger bones than leaner children. The present cross-sectional observational study was undertaken to examine the magnitude of compensatory increases in the spinal bone mineral content (BMC) and area shown by overweight and obese children and adolescents. Vertebral area and BMC of lumbar vertebrae L2-L4 were measured by dual-energy X-ray absorptiometry in 202 boys and 160 girls aged 3-19 years. Subjects were categorized as of normal weight, overweight or obese using international cutoffs for body mass index. Compared with children of healthy weight our overweight and obese children had lower vertebral BMC for their bone area, body height, body weight and pubertal development: ratios and 95% CI for overweight and obese groups were 0.92 (95% CI 0.87-0.97) and 0.88 (95% CI 0.80-0.96) for girls and 0.96 (95% CI 0.91-1.02, NS) and 0.87 (95% CI 0.78-0.96) for boys, respectively. Spinal area was low in overweight and obese girls compared with girls of healthy weight but overweight and obese boys had enlarged their vertebral area appropriately for their increased body size. We conclude that during growth overweight and obese children do not increase their spinal BMC to fully compensate for their excessive weight. Limiting excessive adiposity in childhood and adolescence should help to avoid excessive loading and stresses on the lumbar spine.
Adaptation, Physiological↗
Linked oligodeoxynucleotides show binding cooperativity and can selectively impair replication of deleted mitochondrial DNA templates.
Mutations in mitochondrial DNA (mtDNA) cause a spectrum of human pathologies, which predominantly affect skeletal muscle and the central nervous system. In patients, mutated and wild-type mtDNAs often co-exist in the same cell (mtDNA heteroplasmy). In the absence of pharmacological therapy, a genetic strategy for treatment has been proposed whereby replication of mutated mtDNA is inhibited by selective hybridisation of a nucleic acid derivative to the single-stranded replication intermediate, allowing propagation of the wild-type genome and correction of the associated respiratory chain defect. Previous studies have shown the efficacy of this anti-genomic approach in vitro, targeting pathogenic mtDNA templates with only a single point mutation. Pathogenic molecules harbouring deletions, however, present a more difficult problem. Deletions often occur at the site of two short repeat sequences (4-13 residues), only one of which is retained in the deleted molecule. With the more common larger repeats it is therefore difficult to design an anti-genomic molecule that will bind selectively across the breakpoint of the deleted mtDNA. To address this problem, we have used linker-substituted oligodeoxynucleotides to bridge the repeated residues. We show that molecules can be designed to bind more tightly to the deleted as compared to the wild-type mtDNA template, consistent with the nucleotide sequence on either side of the linker co-operating to increase binding affinity. Furthermore, these bridging molecules are capable of sequence-dependent partial inhibition of replication in vitro.
Base Pairing↗
The determination of complete human mitochondrial DNA sequences in single cells: implications for the study of somatic mitochondrial DNA point mutations.
Studies of single cells have previously shown intracellular clonal expansion of mitochondrial DNA (mtDNA) mutations to levels that can cause a focal cytochrome c oxidase (COX) defect. Whilst techniques are available to study mtDNA rearrangements at the level of the single cell, recent interest has focused on the possible role of somatic mtDNA point mutations in ageing, neurodegenerative disease and cancer. We have therefore developed a method that permits the reliable determination of the entire mtDNA sequence from single cells without amplifying contaminating, nuclear-embedded pseudogenes. Sequencing and PCR-RFLP analyses of individual COX-negative muscle fibres from a patient with a previously described heteroplasmic COX II (T7587C) mutation indicate that mutant loads as low as 30% can be reliably detected by sequencing. This technique will be particularly useful in identifying the mtDNA mutational spectra in age-related COX-negative cells and will increase our understanding of the pathogenetic mechanisms by which they occur.
Alleles↗
An antigenomic strategy for treating heteroplasmic mtDNA disorders.
In mammals, mitochondrial DNA (mtDNA) is the only autonomously replicating source of DNA outside the nucleus. Housed in the mitochondrial matrix, this molecule encodes thirteen polypeptides, all of which are believed to be essential components of the mitochondrial respiratory chain. Defects of the mitochondrial genome can cause severe neurological and multi-systemic disorders. As the genetic defect causes a dysfunction in the terminal stage of oxidative metabolism, there is little potential for pharmacological intervention. Thus, there is currently no effective therapy for these chronic progressive disorders. In the disease state, pathogenic mtDNA molecules often cohabit the same cell and tissue with wild type mtDNA, a situation termed heteroplasmy. Manifestation of biochemical and clinical defects occur only when a threshold level of heteroplasmy has been passed. The mitochondrial genome must be continually turned over. Consequently, if a pathogenic mtDNA molecule were to be targeted to prevent it from replicating, the wild type copy would be given a propagative advantage. Over time, therefore, the biochemical and, potentially, the clinical deficiency could be reversed. This manuscript summarises our attempts to identify such an antigenomic molecule, to localise this molecule to mitochondria and to assess its function in whole cells. Finally, we discuss the importance of identifying and designing new antigenomic molecules which may prove effective in treating patients with disorders of the mitochondrial genome.
DNA Replication↗
Targeting large molecules to mitochondria.
Mitochondrial function is central to a range of cell processes and mitochondrial dysfunction contributes to a number of human diseases. Consequently there is growing interest in delivering large molecules such as nucleic acids, proteins, enzyme mimetics, drugs and probes to mitochondria within cells. The reasons for doing this are to understand how mitochondria function in the cell and to develop therapies for diseases involving mitochondrial damage. Here we review the methods that have been used to target large molecules to mitochondria and discuss some approaches under development.
Animals↗
Targeting peptide nucleic acid (PNA) oligomers to mitochondria within cells by conjugation to lipophilic cations: implications for mitochondrial DNA replication, expression and disease.
The selective manipulation of mitochondrial DNA (mtDNA) replication and expression within mammalian cells has proven difficult. One promising approach is to use peptide nucleic acid (PNA) oligomers, nucleic acid analogues that bind selectively to complementary DNA or RNA sequences inhibiting replication and translation. However, the potential of PNAs is restricted by the difficulties of delivering them to mitochondria within cells. To overcome this problem we conjugated a PNA 11mer to a lipophilic phosphonium cation. Such cations are taken up by mitochondria through the lipid bilayer driven by the membrane potential across the inner membrane. As anticipated, phosphonium-PNA (ph-PNA) conjugates of 3.4-4 kDa were imported into both isolated mitochondria and mitochondria within human cells in culture. This was confirmed by using an ion-selective electrode to measure uptake of the ph-PNA conjugates; by cell fractionation in conjunction with immunoblotting; by confocal microscopy; by immunogold-electron microscopy; and by crosslinking ph-PNA conjugates to mitochondrial matrix proteins. In all cases dissipating the mitochondrial membrane potential with an uncoupler prevented ph-PNA uptake. The ph-PNA conjugate selectively inhibited the in vitro replication of DNA containing the A8344G point mutation that causes the human mtDNA disease 'myoclonic epilepsy and ragged red fibres' (MERRF) but not the wild-type sequence that differs at a single nucleotide position. Therefore these modified PNA oligomers retain their selective binding to DNA and the lipophilic cation delivers them to mitochondria within cells. When MERRF cells were incubated with the ph-PNA conjugate the ratio of MERRF to wild-type mtDNA was unaffected, even though the ph-PNA content of the mitochondria was sufficient to inhibit MERRF mtDNA replication in a cell-free system. This unexpected finding suggests that nucleic acid derivatives cannot bind their complementary sequences during mtDNA replication. In summary, we have developed a new strategy for targeting PNA oligomers to mitochondria and used it to determine the effects of PNA on mutated mtDNA replication in cells. This work presents new approaches for the manipulation of mtDNA replication and expression, and will assist in the development of therapies for mtDNA diseases.
Binding Sites↗
Progressive mitochondrial disease resulting from a novel missense mutation in the mitochondrial DNA ND3 gene.
We describe a 42-year-old man who presented with a progressive history of epilepsy, stroke-like episodes, bilateral optic atrophy, and cognitive decline. Investigation of his muscle biopsy revealed a specific defect in complex I activity. Subsequent analysis of the mitochondrial genome identified a novel heteroplasmic T10191C mutation in the ND3 gene. The mutation was present at lower levels in blood from the patient and unaffected maternal relatives and is the first pathogenic mitochondrial DNA mutation in the ND3 gene to be described.
Adult↗