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Biomedical subjects

P F Chinnery

Publications and source records attributed to P F Chinnery.

At least 19 recordsLinked to original sources
PubMed2000

The spectrum of hearing loss due to mitochondrial DNA defects.

Heteroplasmic mitochondrial DNA (mtDNA) defects are an important cause of neurological disease. Although hearing impairment is common in patients with mtDNA defects, the spectrum and pathophysiology of the hearing loss is not well characterized. We therefore studied the relationship between cochlear and brainstem auditory function in 23 patients harbouring a range of different mtDNA mutations. Based upon the pure tone audiogram, patients fell into three distinct groups: (i) normal hearing, (ii) mild to moderate predominantly high frequency hearing loss, and (iii) severe or profound hearing loss at all frequencies. Within this study group only certain genetic defects were associated with hearing loss, and for individuals harbouring the A3243G point mutation, the severity of the hearing loss correlated with the percentage level of mutated mtDNA (mutation load) in skeletal muscle. The 10 patients who had a moderate hearing loss or less had normal brainstem auditory evoked responses and MRI, but it was not possible to interpret the brainstem auditory evoked responses in 13 patients with severe hearing loss. Otoacoustic emissions were absent in patients with a moderate or more severe hearing loss. These findings are consistent with a predominantly cochlear origin for the hearing deficit, which is determined by the precise genetic defect and the percentage mutation load.

Adult↗
PubMed2000

Very low levels of the mtDNA A3243G mutation associated with mitochondrial dysfunction in vivo.

We studied mitochondrial function in vivo in 2 brothers harboring the mitochondrial DNA A3243G mutation by using magnetic resonance spectroscopy. One brother presented with recurrent strokes and had a mitochondrial respiratory chain complex I defect, with 85% A3243G mutation in his quadriceps. The maximum rate of mitochondrial ATP production in his calf, measured in vivo, was reduced to 21% of the normal mean value. The second brother had mild exercise intolerance, normal muscle histochemistry, and normal respiratory chain activity in vitro. Despite a level of the A3243G mutation of only 5.95% (SD, 4.45; range, 0.7-16.1%) within single muscle fibers from the gastrocnemius muscle, the maximum rate of mitochondrial ATP production in his calf, measured in vivo, was reduced to 35% of the normal mean value. These findings suggest that there may not be a clear genetic threshold level for the expression of the A3243G mutation in skeletal muscle in vivo.

Adult↗
PubMed1999

Nonrandom tissue distribution of mutant mtDNA.

Heteroplasmic mitochondrial DNA (mtDNA) defects are an important cause of inherited human disease. On a cellular level, the percentage of mutant mtDNA is the principal factor behind the expression of the genetic defect. Marked variation in the level of mutant mtDNA among tissues is thought to be responsible for the diverse clinical phenotypes associated with the same pathogenic mtDNA mutation. This study was designed to determine whether the percentage level of a pathogenic mtDNA molecule is determined by a purely random process. The tissue distribution of the A3243G MELAS point mutation was analyzed in five individuals who were members of a family with maternally inherited diabetes and deafness. The level of mutant mtDNA was measured in four tissues in three individuals and three tissues in two individuals. The highest level of mutant mtDNA occurred in skeletal muscle, followed by hair follicles, and then buccal mucosa, with the lowest levels in blood (leucocyte/platelet fraction). The probability of observing any strict hierarchy in family is 4.82 x 10(-5). These results indicate that the distribution of the A3243G mutation is not solely determined by random processes.

Adult↗
PubMed1999

Evaluation of bupivacaine-induced muscle regeneration in the treatment of ptosis in patients with chronic progressive external ophthalmoplegia and Kearns-Sayre syndrome.

PURPOSE: Ptosis is common in patients with mitochondrial disease. Whilst surgical shortening of the levator muscle can mechanically elevate the lid, this procedure does not restore normal movement and leaves patients at risk of corneal exposure due to concomitant ophthalmoparesis. Recent studies have shown that bupivacaine-induced muscle regeneration is capable of reversing the molecular genetic and biochemical defect in patients with mitochondrial myopathies. This study was undertaken to assess the potential of this approach in restoring levator muscle function in patients with mitochondrial disease and ptosis. METHODS: The levator muscle of one eye in five patients with molecularly genetically confirmed mitochondrial DNA disease and ptosis was directly injected with 3 ml of bupivacaine hydrochloride (0.75%). Levator function was compared before and 3 months after the injection. RESULTS: No objective clinical improvement in levator function was detected following bupivacaine administration. DISCUSSION: The lack of functional recovery seen in our patients is most likely to result from a failure of bupivacaine to induce sufficient regeneration necessary to improve levator muscle function. This result indicates that consideration now needs to be given to the use of alternative and more potent myotoxic agents capable of inducing a more widespread regenerative response from the endogenous muscle satellite cells which contain low or undetectable amounts of mutant mitochondrial DNA.

Adult↗
PubMed1999

Peptide nucleic acid delivery to human mitochondria.

Peptide nucleic acids (PNAs) are synthetic polynucleobase molecules, which bind to DNA and RNA with high affinity and specificity. Although PNAs have enormous potential as anti-sense agents, the success of PNA-mediated gene therapy will require efficient cellular uptake and sub-cellular trafficking. At present these mechanisms are poorly understood. To address this, we have studied the uptake of biotinylated PNAs into cultured cell lines using fluorescence confocal microscopy. In human myoblasts, initial punctate staining was followed by the release of PNAs into the cytosol and subsequent localisation and concentration in the nucleus. To determine whether PNAs could also be used as therapeutic agents for mtDNA disease, we attempted to localise PNAs to the mitochondrial matrix. When attached to the presequence peptide of the nuclear-encoded human cytochrome c oxidase (COX) subunit VIII, the biotinylated PNA was successfully imported into isolated organelles in vitro. Furthermore, delivery of the biotinylated peptide-PNA to mitochondria in intact cells was confirmed by confocal microscopy. These studies demonstrate that biotinylated PNAs can be directed across cell membranes and to a specific sub-cellular compartment within human cells - highlighting the importance of these novel molecules for human gene therapy.

Animals↗
PubMed1999

Relaxed replication of mtDNA: A model with implications for the expression of disease.

Heteroplasmic mtDNA defects are an important cause of human disease with clinical features that primarily involve nondividing (postmitotic) tissues. Within single cells the percentage level of mutated mtDNA must exceed a critical threshold level before the genetic defect is expressed. Although the level of mutated mtDNA may alter over time, the mechanism behind the change is not understood. It currently is not possible to directly measure the level of mutant mtDNA within living cells. We therefore developed a mathematical model of human mtDNA replication, based on a solid foundation of experimentally derived parameters, and studied the dynamics of intracellular heteroplasmy in postmitotic cells. Our simulations show that the level of intracellular heteroplasmy can vary greatly over a short period of time and that a high copy number of mtDNA molecules delays the time to fixation of an allele. We made the assumption that the optimal state for a cell is to contain 100% wild-type molecules. For cells that contain pathogenic mutations, the nonselective proliferation of mutant and wild-type mtDNA molecules further delays the fixation of both alleles, but this leads to a rapid increase in the mean percentage level of mutant mtDNA within a tissue. On its own, this mechanism will lead to the appearance of a critical threshold level of mutant mtDNA that must be exceeded before a cell expresses a biochemical defect. The hypothesis that we present is in accordance with the available data and may explain the late presentation and insidious progression of mtDNA diseases.

Alleles↗
PubMed1999

An mtDNA mutation in the initiation codon of the cytochrome C oxidase subunit II gene results in lower levels of the protein and a mitochondrial encephalomyopathy.

A novel heteroplasmic 7587T-->C mutation in the mitochondrial genome which changes the initiation codon of the gene encoding cytochrome c oxidase subunit II (COX II), was found in a family with mitochondrial disease. This T-->C transition is predicted to change the initiating methionine to threonine. The mutation load was present at 67% in muscle from the index case and at 91% in muscle from the patient's clinically affected son. Muscle biopsy samples revealed isolated COX deficiency and mitochondrial proliferation. Single-muscle-fiber analysis revealed that the 7587C copy was at much higher load in COX-negative fibers than in COX-positive fibers. After microphotometric enzyme analysis, the mutation was shown to cause a decrease in COX activity when the mutant load was >55%-65%. In fibroblasts from one family member, which contained >95% mutated mtDNA, there was no detectable synthesis or any steady-state level of COX II. This new mutation constitutes a new mechanism by which mtDNA mutations can cause disease-defective initiation of translation.

Adult↗
PubMed1999

Diagnostic utility of metabolic exercise testing in a patient with cardiovascular disease.

Disproportionate exercise limitation in patients with cardiovascular disease is a common problem faced by clinical cardiologists and other physicians. Symptoms may be attributed to psychological factors or hypothetical pathophysiological mechanisms that are difficult to confirm clinically. This case report describes how the use of metabolic exercise testing in a 28 year old woman with morphologically and haemodynamically mild hypertrophic cardiomyopathy and severe exercise limitation led to the diagnosis of an alternative cause for the patient's symptoms, namely a primary disturbance of the mitochondrial respiratory chain probably caused by a nuclear encoded gene defect.

Adult↗
PubMed1999

Mitochondrial DNA analysis: polymorphisms and pathogenicity.

The investigation of mtDNA disease can be relatively straightforward if a person has a recognisable phenotype and if it is possible to identify a known pathogenic mtDNA mutation. The difficulties arise when no known mtDNA defect can be found, or when the clinical abnormalities are complex and not easily matched to those of the more common mitochondrial disorders. We will describe here the difficulties that can be encountered during the identification of pathogenic mtDNA mutations and the approaches that can be used to confirm, or eliminate, a likely pathogenic role, in either single gene diseases or in multifactorial disorders.

Animals↗
PubMed1998

A novel mitochondrial DNA point mutation in the tRNA(Ile) gene: studies in a patient presenting with chronic progressive external ophthalmoplegia and multiple sclerosis.

We report a new mutation, a G to A transition at nucleotide position 4298 within the mitochondrial tRNA(Ile) gene in a patient with chronic progressive external ophthalmoplegia and multiple sclerosis. The mutation, which alters an evolutionary conserved nucleotide within the anticodon stem, was heteroplasmic in skeletal muscle but was not present in the patient's blood. Single fibre PCR analysis revealed significantly higher levels of the G4298A mutation in cytochrome c oxidase (COX) negative fibres than in COX-positive fibres. This mutation represents the seventh pathogenic nucleotide substitution to be found in this gene and as such confirms the tRNA(Ile) gene as a susceptible "hot spot" for mitochondrial DNA point mutations. Of particular interest is that this patient has the clinical features of both multiple sclerosis and a mitochondrial DNA disorder.

Animals↗
PubMed1998

Muscle pain as a prominent feature of facioscapulohumeral muscular dystrophy (FSHD): four illustrative case reports.

Clinical studies of facioscapulohumeral muscular dystrophy (FSHD) rarely report muscle pain as a significant feature of the condition. We report four adult patients with FSHD in whom muscle pain was a presenting complaint and remains their most disabling symptom. These four patients were investigated using a pain questionnaire and diary. Inflammatory and metabolic causes of muscle pain were sought by muscle biopsy and a range of biochemical investigations. All patients reported between three and seven different pains of varying site and nature. None of the group had more than one painfree day per month and all complained of disturbed sleep. While some pains could potentially be attributed to postural problems, others were clearly myalgic in nature, though most often not specifically exercise-related. These myalgic pains could be particularly difficult to control. Results of metabolic investigations and muscle biopsy revealed no clue to the pathogenesis of these pains and there was no evidence for any exceptional inflammatory response. We believe that pain in FSHD is an under-reported but significant symptom and that further work is necessary to determine its prevalence, understand its cause and provide effective treatment.

Adult↗