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A Majander

Publications and source records attributed to A Majander.

At least 19 recordsLinked to original sources
PubMed2001

ATP, phosphocreatine and lactate in exercising muscle in mitochondrial disease and McArdle's disease.

We studied exercise-induced changes in the adenosine triphosphate (ATP), phosphocreatine (PCr), and lactate levels in the skeletal muscle of mitochondrial patients and patients with McArdle's disease. Needle muscle biopsy specimens for biochemical measurement were obtained before and immediately after maximal short-term bicycle exercise test from 12 patients suffering from autosomal dominant and recessive forms of progressive external ophthalmoplegia and multiple deletions of mitochondrial DNA (adPEO, arPEO, respectively), five patients with mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) 3243 A-->G point mutation, and four patients with McArdle's disease. Muscle ATP and PCr levels at rest or after exercise did not differ significantly from those of the controls in any patient group. In patients with mitochondrial disease, muscle lactate tended to be lower at rest and increase more during exercise than in controls, the most remarkable rise being measured in patients with adPEO with generalized muscle symptoms and in patients with MELAS point mutation. In McArdle patients, the muscle lactate level decreased during exercise. No correlation was found between the muscle ATP and PCr levels and the respiratory chain enzyme activity.

Adenosine Triphosphate↗
PubMed1998

Neuroradiologic findings in children with mitochondrial disorders.

PURPOSE: We report the neuroradiologic findings in 25 children with various mitochondrial diseases. METHODS: Twenty-two children with a mitochondrial disorder had MR imaging of the brain and three children had CT studies. In all cases, the diagnosis was based on examination of muscle morphology, analysis of oxygen consumption and respiratory chain enzyme activity in isolated muscle mitochondria, and analysis of rearrangements of the mitochondrial DNA. RESULTS: Fifteen patients were found to have the classical syndromes of mitochondrial diseases. Four children had Kearns-Sayre syndrome, but only one had the typical neuroradiologic findings of basal ganglia and brain stem lesions, T2 hyperintensity of the cerebral white matter, and cerebellar atrophy; the others had nonspecific or normal findings. Eight patients had Leigh syndrome, and all showed changes in the putamina. Involvement of the caudate nuclei, globus pallidi, thalami, and brain stem was common, and diffuse supratentorial white matter T2 hyperintensity was seen in two of these patients. Three patients had mitochondrial encephalopathy with lactic acidosis and strokelike episodes (MELAS), with infarctlike lesions that did not correspond to the vascular territories. Ten children with complex I or IV deficiencies and abnormal muscle morphology had nonspecific imaging findings, such as atrophy and abnormal or delayed myelination. One patient with combined complex I and IV deficiency had extensive white matter changes. None of the patients with clinical encephalopathy had normal findings. CONCLUSION: MR imaging is helpful in the diagnosis of the classical mitochondrial diseases; however, nonspecific findings are common.

Adolescent↗
PubMed1997

Mutations in subunit 6 of the F1F0-ATP synthase cause two entirely different diseases.

A lowered efficiency of oxidative phosphorylation was recently found in a Leber hereditary optic neuropathy (LHON) proband carrying a mutation in the mtDNA gene for subunit 6 of the membrane-bound F0 segment of the F1F0-ATP synthase [9]. This phenotype was transferred to cytoplasmic hybrid cells together with the mutation, proving its functional significance. Increasing the respiratory rate in the mitochondria from this mutant raised the ATP/2e- ratio back to normal values. A different mutation in the same mtDNA gene has been found in patients with the NARP syndrome [10]. Although the ATP/2e- ratio is also decreased in this mutant, in this case an increase in the respiratory rate could not compensate for it. Whilst both mutations affect subunit 6 of the proton-translocating F0 segment, the LHON mutation induces a proton leak whereas the NARP mutation blocks proton translocation. Hence, the latter will have much more destructive metabolic consequences in agreement with the large clinical differences between the two diseases.

Adenosine Triphosphate↗
PubMed1997

Autosomal dominant progressive external ophthalmoplegia with multiple deletions of mtDNA: clinical, biochemical, and molecular genetic features of the 10q-linked disease.

Autosomal dominant progressive external ophthalmoplegia (adPEO) is a mitochondrial disease characterized by accumulation of multiple large deletions of mtDNA in patients' tissues. We previously showed that the disease is genetically heterogeneous by assigning two nuclear loci predisposing to mtDNA deletions: one on chromosome 10q 23.3-24.3 in a Finnish family and one on 3p 14.1-21.2 in three Italian families. To reveal any locus-specific disease features, we report here the clinical, biochemical, and molecular genetic characteristics of the 10q-linked disease in the single family reported to date. All seven patients and four asymptomatic subjects had ragged-red fibers and multiple deletions of mtDNA in their muscle. Ptosis and external ophthalmoplegia were the major clinical findings, and depression or avoidant personality traits were frequently, but not consistently, present in the subjects carrying mutant mtDNA. In six of the subjects with mutant mtDNA, the activities of the respiratory chain complexes I or IV, or both, were below or within the low normal range. Two autopsy studies revealed the characteristic distribution of mutant mtDNA in these patients: highest proportion of mutant mtDNA is found in different parts of the brain, followed by the skeletal and ocular muscle, and the heart.

Adult↗
PubMed1996

Catalytic activity of complex I in cell lines that possess replacement mutations in the ND genes in Leber's hereditary optic neuropathy.

Short-chain ubiquinone analogues act as electron acceptors and as inhibitors in the lymphoblast mitochondria of ND1/3460 mutants, which indicates structural changes in the ubiquinone-binding domain of Complex I in this mutant. The ND4/11778 mutant and two secondary ND5 mutants studied are associated with reductions of at least 50, 35 and 30% in the catalytic rate constant, respectively. However, the efficiency of oxidative phosphorylation is unaffected in all these ND mutants. The rate of respiration is only slightly limited by Complex I in lymphoblast mitochondria. Consequently, there is a 30-35% reduction in the electron flow through Complex I compared with that through Complex II, and an increased lactate/pyruvate ratio, in the ND1 and ND4 mutants, but these factors were unaffected in the secondary ND5 mutants. Energy metabolism is thus less severely affected in the secondary mutants than in the primary mutants, which supports the division into these two categories. An increased ubiquinone-10 content in the mitochondrial membrane of all the mutants, and enhanced succinate dehydrogenase and citrate synthase activities in the ND4 mutant, are proposed to be compensatory changes. The efficiency of these changes and the level of kinetic limitation of respiration by Complex I in each tissue are proposed to determine the clinical development of the disease.

Catalysis↗
PubMed1996

Severe hyperprostaglandin E syndrome with hyperthyroidism--studies of pathogenetic mechanisms.

Hyperprostaglandin E syndrome is a rare disease usually presenting with renal symptoms such as polyuria, polyhydramnios, hypercalciuria, hypokalaemia, and recurrent episodes of extreme fever, diarrhoea, and convulsions. We report a severe variant of this syndrome with obvious pain and prostaglandin E2 (PGE2)-stimulated hyperthyroidism, an association not previously described. Urinary excretion of PGE2 and its metabolite 7 alpha-hydroxy-5,11-diketotetranorprosta-1,16-dioic acid were markedly increased above normal levels (to 53.3 and 1895 ng/h per 1.73 m2, respectively). We studied oxidative capacity of peroxisomes and mitochondria, the sites where PGE2 oxidation takes place. A generalized mitochondrial disease could be ruled out and no deficiency was found in liver peroxisomal oxidases. The basic pathology of hyperprostaglandin E syndrome remains unsolved.

Cyclooxygenase Inhibitors↗
PubMed1996

Pathology of skeletal muscle and impaired respiratory chain function in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency with the G1528C mutation.

Lactic acidosis and mitochondrial abnormalities have been reported in long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency. We studied muscle morphology and the respiratory chain function in ten patients with LCHAD deficiency and the G1528C mutation. In eight cases the light microscopy of muscle specimens showed fatty infiltration and fibre degeneration. The degenerated fibres appeared as ragged red fibres in four cases. Electron microscopy revealed enlarged mitochondria often with swollen appearance in four out of seven patients. The number of mitochondria had also increased. Complex I associated enzyme activities in muscle mitochondria were decreased in five out of seven patients, and in three of them Complex II or II + III associated activities were also affected. We suggest that the reason for respiratory chain dysfunction and structural changes of mitochondria is the accumulation of toxic intermediates of fatty acid beta-oxidation in mitochondria. Because these changes may confound the differential diagnostics between LCHAD deficiency and respiratory chain defects, awareness of their frequency is important.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1995

Palmitate oxidation in muscle mitochondria of patients with the juvenile form of neuronal ceroid-lipofuscinosis.

The finding that the intracellular storage material in juvenile neuronal ceroid lipofuscinosis (JNCL) consists of the subunit c of ATP synthase prompted us to study energy conservation in JNCL patients. The activities of respiratory chain enzymes in isolated muscle mitochondria from 8 JNCL cases were normal, but oxidation of palmitate was reduced in 6 patients. The degree of reduction was related to the age of the patients. None of the patients had clinical symptoms or laboratory findings of impaired energy conservation, which suggest that the reduced palmitate oxidation was not associated with a major defect in fatty acid oxidation.

Adolescent↗
PubMed1995

Diagnosis of fatal infantile defects of the mitochondrial respiratory chain: age dependence and postmortem analysis of enzyme activities.

We studied two diagnostic aspects of fatal infantile defects of the mitochondrial respiratory chain: the age dependence of muscle mitochondrial enzyme activities and the reliability of diagnosis from autopsy samples. In morphologically normal quadriceps muscle samples of 46 children between the ages of 3 days and 15 years, activities of complex I plus III (NADH:cytochrome c oxidoreductase) and complex II plus III (succinate:cytochrome c oxidoreductase) increased 2-fold during the first three years of life, while that of complex II (succinate dehydrogenase), complex IV (cytochrome c oxidase), and citrate synthase did not show significant correlation with age. We suggest that these changes are related to age and stress the importance of strictly age-matched controls when diagnosing a mitochondrial disease of early childhood. The value of autopsy samples in diagnostic studies was evaluated by comparing mitochondrial enzyme activities in quadriceps muscle from autopsies and from surgical biopsies. In quadriceps muscle mitochondria, all the enzyme activities studied remained stable for at least 3 h after death. Using age-matched controls and autopsy samples, we diagnosed a respiratory chain enzyme deficiency in two infants, and the defects were confirmed in cultured skin fibroblasts.

Adolescent↗
PubMed1995

Correlation between the clinical symptoms and the proportion of mitochondrial DNA carrying the 8993 point mutation in the NARP syndrome.

We describe a four-generation family with a maternally inherited mitochondrial disorder. The symptoms were restricted to the CNS and muscle, the most common features being subacute necrotizing encephalomyopathy, cognitive impairment, ataxia, retinitis pigmentosa, infantile spasms, and optic atrophy. A point mutation at the nucleotide 8993 of the gene encoding subunit 6 of the ATP synthase, associated with the neurogenic muscle weakness, ataxia, retinitis pigmentosa (NARP) syndrome, was shown to be inherited maternally in this family, and a clear correlation was found between the clinical severity of the disease and the proportion of mutant mtDNA. Analysis of oxidative phosphorylation in mitochondria carrying 80% mutant mitochondrial DNA showed a reduction of the ATP generation rate coupled to substrate oxidation.

Adolescent↗
PubMed1994

Diphenyleneiodonium inhibits reduction of iron-sulfur clusters in the mitochondrial NADH-ubiquinone oxidoreductase (Complex I).

Diphenyleneiodonium (DPI) inhibits the mitochondrial NADH-ubiquinone oxidoreductase (Complex I) on the substrate side of the Fe-S clusters. In the inhibited NADH-supplemented state all of the Fe-S clusters are oxidized, whereas the reduced minus oxidized difference spectrum of the protein-bound FMN can be visualized. It is characterized by troughs at 370 and 450 nm and a small increase of absorbance in the 500-700-nm region. DPI probably reacts irreversibly with FMN, because oxidation of FMN is blocked even after its extraction from the enzyme. Inhibition requires preincubation of enzyme in the presence of NADH and DPI. The lower the NADH/NAD+ ratio or the pH, or the higher the NAD+/DPI ratio, the more DPI is required for inhibition. NAD+ and DPI apparently compete for a common site. Both ubiquinone and dichlorophenolindophenol reductase activities are fully blocked by DPI, whereas the ferricyanide reductase activity is inhibited by 75%. Similar results were found with Complex I and two rotenone-insensitive preparations, subcomplex I lambda and the flavoprotein fraction. DPI also inhibits NADH oxidation by bacterial NADH-ubiquinone oxidoreductase-1 (NDH-1) in membranes of Paracoccus denitrificans and Escherichia coli.

Electron Spin Resonance Spectroscopy↗
PubMed1994

Studies on the proton-translocating NADH:ubiquinone oxidoreductases of mitochondria and Escherichia coli using the inhibitor 1,10-phenanthroline.

Mitochondrial NADH:ubiquinone oxidoreductase (complex I) is uncompetitively inhibited by 1,10-phenanthroline (OP). EPR spectroscopy of submitochondrial particles indicates that OP, similarly to rotenone, inhibits electron transfer between the Fe-S clusters of complex I and the ubiquinone pool. The proton-translocating NADH dehydrogenase (NDH1) of E. coli is more sensitive to OP than is NDH1 of Paracoccus. EPR spectroscopy of membranous E. coli NDH1 shows that two slow- and one fast-relaxing Fe-S clusters become detectable upon reduction by NADH in the presence of OP. However, none of them resembles the mitochondrial cluster 2.

Animals↗
PubMed1993

Quantification of tRNA3243(Leu) point mutation of mitochondrial DNA in MELAS patients and its effects on mitochondrial transcription.

The MELAS syndrome is a mitochondrial encephalomyopathy associated with a point mutation at nucleotide 3243 of mitochondrial DNA (mtDNA). The same mutation has also been found in patients with maternally inherited diabetes mellitus. The mutation occurs within a sequence needed for termination of mitochondrial transcription downstream of the ribosomal RNA (rRNA) genes, thus possibly reducing rRNA synthesis in relation to more distal transcripts. This study presents a family in which maternally transmitted diabetes and MELAS syndrome overlap, and a suggestive correlation between the amount of mutant mtDNA and clinical symptoms is observed. Mutant mtDNA was quantified in several tissues of a newborn infant and the highest amount of mutant mtDNA was found in the placenta, which is promising for the development of genetic counselling in MELAS. The consequences of the MELAS mutation were further studied in cultured clonal myoblasts. We found that the myoblasts with 93% of mutant mtDNA terminate the mitochondrial transcription, resulting in a steady-state amount of 16S rRNA 45 times as high as the more distal transcripts. However, myoblasts with a deletion of mtDNA not involving the transcription termination site had 120 times as much 16S rRNA as the distal transcripts. In both the MELAS myoblasts and in those with a deletion of mtDNA the amount of 16S rRNA increased as the mutant mtDNA increased, suggesting that the production of ribosomal RNAs is a response to the translational defect caused by the mutation. We present evidence here that the MELAS mutation causes a defect in transcription termination, thus leading to no absolute deficiency of ribosomal RNAs, but to a reduced capacity to compensate the defective translation.

Adolescent↗
PubMed1992

Inherited idiopathic dilated cardiomyopathy with multiple deletions of mitochondrial DNA.

Idiopathic dilated cardiomyopathy (DCM) is often familial, but the pathogenetic mechanisms of DCM are unknown. We report a woman and her son who both died of DCM. The son's cardiac and skeletal muscles showed a high proportion of mitochondrial DNA (mtDNA) with multiple large deletions by Southern-blot hybridisation and polymerase chain reaction analyses. Amplification of the mother's cardiac mtDNA from 20-year-old paraffin-embedded sections showed that she also had deletions of mtDNA. These data suggest that a subgroup of inherited DCMs is associated with mtDNA mutations.

Adolescent↗
PubMed1992

Disorders associated with multiple deletions of mitochondrial DNA.

Multiple deletions of mitochondrial DNA (mtDNA) have recently been described in a number of patients with neurological disorders. Most cases have been clinically characterized by autosomal dominant inheritance, adult onset, and a slowly progressive course with external ophthalmoplegia and muscle weakness. Some patients have had evidence of central or peripheral nervous system involvement or episodes of myoglobinuria. Muscle biopsy findings include ragged-red fibres (RRF), muscle fibres with absent COX-activity and abundant abnormal mitochondria with paracrystalline inclusions. Biochemically, a generalized reduction in the activities of mtDNA-encoded enzymes is observed in skeletal muscle. Southern blotting or PCR analysis reveal multiple populations of deleted mtDNA. The deletions occur at multiple sites between the replication initiation sites, involving a large portion of mtDNA, and most deletions seem to be flanked by direct sequence repeats, shown to be "hot spots" in the case of single large deletions. Apparently, a defect in a nuclear gene results in multiple deletions of mtDNA. Both clinical, genetic and molecular genetic observations indicate heterogeneity of this new disease category, apparently based on a disturbance in the "cross-talk" between the nuclear and the mitochondrial genomes.

DNA, Mitochondrial↗