Mitochondrial DNA deletions in progressive external ophthalmoplegia and Kearns-Sayre syndrome

We investigated the correlations of deletions of mitochondrial DNA in skeletal muscle with clinical manifestations of mitochondrial myopathies, a group of disorders defined either by biochemical abnormalities of mitochondria or by morphologic changes causing a ragged red appearance of the muscle fibers histochemically. We performed genomic Southern blot analysis of muscle mitochondrial DNA from 123 patients with different mitochondrial myopathies or encephalomyopathies. Deletions were found in the mitochondrial DNA of 32 patients, all of whom had progressive external ophthalmoplegia. Some patients had only ocular myopathy, whereas others had Kearns-Sayre syndrome, a multisystem disorder characterized by ophthalmoplegia, pigmentary retinopathy, heart block, and cerebellar ataxia. The deletions ranged in size from 1.3 to 7.6 kilobases and were mapped to different sites in the mitochondrial DNA, but an identical 4.9-kilobase deletion was found in the same location in 11 patients. Biochemical analysis showed decreased activities of NADH dehydrogenase, rotenone-sensitive NADH-cytochrome c reductase, succinate-cytochrome c reductase, and cytochrome c oxidase, four enzymes of the mitochondrial respiratory chain containing subunits encoded by mitochondrial DNA. We conclude that deletions of muscle mitochondrial DNA are associated with ophthalmoplegia and may result in impaired mitochondrial function. However, the precise relation between clinical and biochemical phenotypes and deletions remains to be defined.

Duchenne muscular dystrophy: deficiency of dystrophin at the muscle cell surface

Dystrophin is the altered gene product in Duchenne muscular dystrophy (DMD). We used polyclonal antibodies against dystrophin to immunohistochemically localize the protein in human muscle. In normal individuals and in patients with myopathies other than DMD, dystrophin was localized to the sarcolemma of the fibers. The protein was absent or markedly deficient in DMD. The sarcolemmal localization of dystrophin is consistent with other evidence that there are structural and functional abnormalities of muscle surface membranes in DMD.

Action of cytochalasin D on cells of established lines. I. Early events

HeLa, Vero, L, HEp2, and MDBK cells respond immediately to 0.2-0.5 microg/ml cytochalasin D (CD) with sustained contraction (contracture), loss of microvilli, expression of endoplasmic contents (zeiosis), nuclear protrusion, and extension of cytoplasmic processes. The development of these changes is depicted, and the dose-response patterns in these cell lines are described. MDBK is generally most resistant and HeLa most sensitive to these effects of CD. Cells in G(1) are most sensitive to CD; responsiveness decreases progressively during early S and is least in mid S through G(2). CD inhibits transport of [(14)C]deoxyglucose in HeLa by about 45% but has no significant effect on hexose uptake in Vero and MDBK; sugar transport is thus apparently unrelated to any morphologic effect of CD. Although spreading and attachment are impeded, CD does not decrease and may even enhance the adhesiveness of established monolayers. Contraction appears to be a primary early effect of CD, upon which other visible changes follow. It is prevented by some inhibitors of energy metabolism (deoxyglucose and dinitrophenol) and does not occur in glycerinated models without ATP. The possible bases of the contractile response to CD are discussed. Although direct or indirect action of CD on some microfilaments may occur, a generalized structural disruption of contractile filaments by CD is considered unlikely.

Mitochondrial encephalomyopathy with coenzyme Q10 deficiency

Coenzyme Q10 (CoQ10) transfers electrons from complexes I and II of the mitochondrial respiratory chain to complex III. There is one published report of human CoQ10 deficiency describing two sisters with encephalopathy, proximal weakness, myoglobinuria, and lactic acidosis. We report a patient who had delayed motor milestones, proximal weakness, premature exertional fatigue, and episodes of exercise-induced pigmenturia. She also developed partial-complex seizures. Serum creatine kinase was approximately four times the upper limit of normal and venous lactate was mildly elevated. Skeletal muscle biopsy revealed many ragged-red fibers, cytochrome c oxidase-deficient fibers, and excess lipid. In isolated muscle mitochondria, impaired oxygen consumption was corrected by the addition of decylubiquinone. During standardized exercise, ventilatory and circulatory responses were compatible with a defect of oxidation-phosphorylation, which was confirmed by near-infrared spectroscopy analysis. Biochemical analysis of muscle extracts revealed decreased activities of complexes I+II and I+III, while CoQ10 concentration was less than 25% of normal. With a brief course of CoQ10 (150 mg daily), the patient reported subjective improvement. The triad of CNS involvement, recurrent myoglobinuria, and ragged-red fibers should alert clinicians to the possibility of CoQ10 deficiency.

Action of cytochalasin D on cells of established lines. II. Cortex and microfilaments

Cells in culture exposed to cytochalasin D (CD) rapidly undergo a long-sustained tonic contraction. Coincident with this contracture the thin microfilaments of the cortex become compacted into feltlike masses. The ravelled filaments of these masses remain actinlike and bind heavy meromyosin; they are not disrupted or disaggregated, but rather, appear to represent a contracted state of the microfilament apparatus of the cell cortex. On continued exposure to CD, 'myoid' bundles, containing thick, dense filaments, and larger fusiform or ribbonlike, putatively myosinoid, aggregates may appear. These appearances are interpreted as consequences of a state of hypercontraction without relaxation induced by CD. They do not occur in CD-treated cells prevented from contracting by inhibitors of energy metabolism, and are readily reversible on withdrawal of CD. Extensive ordered arrays of thin microfilaments develop in cells which are reextending during early recovery.

Widespread tissue distribution of mitochondrial DNA deletions in Kearns-Sayre syndrome

We performed Southern analysis of mitochondrial DNA (mtDNA) in 6 tissues from a patient with Kearns-Sayre syndrome and found a single deletion of 4.9 kb in all tissues. The percentage of deleted mtDNAs varied widely between tissues, from only 4% in smooth muscle to approximately 50% in skeletal muscle. Samples of DNA obtained from 3 different skeletal muscles and from separate areas of individual tissues showed little variation in percentage of deleted mtDNA. Biochemical analysis showed no clear correlation between mitochondrial enzyme activity and deleted mtDNAs.

Extracellular creatine regulates creatine transport in rat and human muscle cells

Muscle cells do not synthesize creatine; they take up exogenous creatine by specific Na+-dependent plasma membrane transporters. We found that extracellular creatine regulates the level of expression of these creatine transporters in L6 rat muscle cells. L6 myoblasts maintained for 24 hr in medium containing 1 mM creatine exhibited 1/3rd of the creatine transport activity of cells maintained for 24 hr in medium without creatine. Down-regulation of creatine transport was partially reversed when creatine-fed L6 cells were incubated for 24 hr in medium lacking creatine. Down-regulation of creatine transport occurred independently of amino acid and glucose transport. Furthermore, the down-regulation of creatine transporters by extracellular creatine was slowed by inhibitors of protein synthesis. These results suggest that creatine induces the expression of a protein that functionally inactivates the creatine transporters. Regulation of creatine transport by extracellular creatine also was observed in L6 myotubes and in cultures of human myoblasts and myotubes. Hence, the activity of creatine transport represents another site for the regulation of creatine homeostasis.

Action of cytochalasin D on cells of established lines. III. Zeiosis and movements at the cell surface

The projection of knobby protuberances at the cell surface (zeiosis) is a general cellular response to cytochalasin D (CD), resulting from herniation of endoplasm through undefended places of the cortex during cell contractions and displacement of microfilaments induced by CD. Zeiosis is prevented by agents that interfere with the contractile response to CD, such as inhibitors of energy metabolism or cyclic AMP. The developed protrusions, which remain relatively stable in the presence of CD, contain chiefly mono- or subribosomes, and occasionally other organelles normally resident in endoplasm; compact microfilament felt occupies their bases and extends into their proximal stalks. Protein synthesis in the knobs is less than half of that in the polyribosome-containing endoplasm residual in the main body of the cell. Knobs first protrude singly near the margin of the contracting cells and rapidly cluster into small groups in the periphery even at lower temperature. The clusters then migrate centripetally and coalesce into a large aggregate near the apex of the immobilized and retracted cell: this movement is energy- and temperature-dependent. Aggregation is more prominent and stable in cell lines of epithelial derivation than in fibroblastic or other lines in which nuclear extrusion occurs more readily. The latter is regarded as a special manifestation of zeiosis. Macromarkers, such as latex spherules, migrate like the zeiotic knobs on the cell surfaces in the presence of CD. The aggregated knobs, although persistent for days in the presence of CD, are rapidly recessed after withdrawal of the agent as ruffling is resumed and the cells spread. These movements are discussed in terms of current concepts of mobility of the cell membrane.

Isolation of a cDNA clone encoding subunit IV of human cytochrome c oxidase

We have isolated a full-length human liver cDNA clone specifying the nuclear-encoded subunit IV of the human mitochondrial respiratory chain enzyme, cytochrome c oxidase (COX; EC 1.9.3.1). The human cDNA clone is highly homologous to its bovine counterpart in the coding regions for both the mature polypeptide and the presequence, and the gene is evolving more slowly than that of any of the three mitochondrially encoded COX subunit genes. We find no preliminary evidence for tissue-specific isoforms of COX subunit IV, as Northern analysis of muscle, liver, and HeLa cell RNA shows an identically sized transcript in each cell type.

Co-cultivation of fungal and microalgal cells as an efficient system for harvesting microalgal cells, lipid production and wastewater treatment

The challenges which the large scale microalgal industry is facing are associated with the high cost of key operations such as harvesting, nutrient supply and oil extraction. The high-energy input for harvesting makes current commercial microalgal biodiesel production economically unfeasible and can account for up to 50% of the total cost of biofuel production. Co-cultivation of fungal and microalgal cells is getting increasing attention because of high efficiency of bio-flocculation of microalgal cells with no requirement for added chemicals and low energy inputs. Moreover, some fungal and microalgal strains are well known for their exceptional ability to purify wastewater, generating biomass that represents a renewable and sustainable feedstock for biofuel production. We have screened the flocculation efficiency of the filamentous fungus A. fumigatus against 11 microalgae representing freshwater, marine, small (5 µm), large (over 300 µm), heterotrophic, photoautotrophic, motile and non-motile strains. Some of the strains are commercially used for biofuel production. Lipid production and composition were analysed in fungal-algal pellets grown on media containing alternative carbon, nitrogen and phosphorus sources contained in wheat straw and swine wastewater, respectively. Co-cultivation of algae and A. fumigatus cells showed additive and synergistic effects on biomass production, lipid yield and wastewater bioremediation efficiency. Analysis of fungal-algal pellet's fatty acids composition suggested that it can be tailored and optimised through co-cultivating different algae and fungi without the need for genetic modification.

Protection against quinolinic acid-mediated excitotoxicity in nigrostriatal dopaminergic neurons by endogenous kynurenic acid

Endogenous excitotoxins have been implicated in the degeneration of dopaminergic neurons in the substantia nigra compacta of patients with Parkinson's disease. One such agent quinolinic acid is an endogenous excitatory amino acid receptor agonist. This study examined whether an increased level of endogenous kynurenic acid, an excitatory amino acid receptor antagonist, can protect nigrostriatal dopamine neurons against quinolinic acid-induced excitotoxic damage. Nigral infusion of quinolinic acid (60 nmoles) or N-methyl-D- aspartate (15 nmoles) produced a significant depletion in striatal tyrosine hydroxylase activity, a biochemical marker for dopaminergic neurons. Three hours following the intraventricular infusion of nicotinylalanine (5.6 nmoles), an agent that inhibits kynureninase and kynurenine hydroxylase activity, when combined with kynurenine (450 mg/kg i.p.), the precursor of kynurenic acid, and probenecid (200 mg/kg i.p.), an inhibitor of organic acid transport, the kynurenic acid in the whole brain and substantia nigra was increased 3.3-fold and 1.5-fold respectively when compared to rats that received saline, probenecid and kynurenine. This elevation in endogenous kynurenic acid prevented the quinolinic acid-induced reduction in striatal tyrosine hydroxylase. However, 9 h following the administration of nicotinylalanine with kynurenine and probenecid, a time when whole brain kynurenic acid levels had decreased 12-fold, quinolinic acid injections produced a significant depletion in striatal tyrosine hydroxylase. Intranigral infusion of quinolinic acid in rats that received saline with kynurenine and probenecid resulted in a significant depletion of ipsilateral striatal tyrosine hydroxylase. Administration of nicotinylalanine in combination with kynurenine and probenecid also blocked N-methyl-D-aspartate-induced depletion of tyrosine hydroxylase. Tyrosine hydroxylase immunohistochemical assessment of the substantia nigra confirmed quinolinic acid-induced neuronal cell loss and the ability of nicotinylalanine in combination with kynurenine and probenecid to protect neurons from quinolinic acid-induced toxicity. The present study demonstrates that increases in endogenous kynurenic acid can prevent the loss of nigrostriatal dopaminergic neurons resulting from a focal infusion of quinolinic acid or N-methyl-D-aspartate. The strategy of neuronal protection by increasing the brain kynurenic acid may be useful in retarding cell loss in Parkinson's disease and other neurodegenerative diseases where excitotoxic mechanisms have been implicated.

Human muscle phosphoglycerate mutase deficiency: newly discovered metabolic myopathy

Muscle phosphoglycerate mutase activity was decreased (5.7 percent of the lowest control value) in a 52-year-old man with intolerance for strenuous exercise and recurrent pigmenturia since adolescence. All of the other enzymes of glycolysis had normal activities, and glycogen concentration was normal. Electrophoretic, heat lability, and mercury inhibition studies showed that the small residual activity in the patient's muscle was represented by the brain (BB) isoenzyme of phosphoglycerate mutase, suggesting a genetic defect of the M subunit which predominates in normal muscle. The prevalence of the BB isoenzyme in other tissues, including muscle culture, may explain why symptoms were confined to muscle.

Cytochrome c oxidase deficiency

Cytochrome c oxidase (COX) is a complex enzyme composed of 13 subunits, three of which are encoded by the mitochondrial DNA (mtDNA). The other 10 subunits are encoded by the nuclear DNA, synthesized in the cytoplasm, and transported into the mitochondria. The complexity of the enzyme and its dual genetic control explain the heterogeneity of clinical phenotypes associated with COX deficiency. There are two major syndromes, one characterized by muscle involvement (fatal infantile or benign infantile myopathy), the other dominated by brain disease (Leigh syndrome, myoclonic epilepsy with ragged red fibers, Menkes' disease). Partial defects of COX have been shown in muscle of patients with progressive external ophthalmoplegia, either alone (ocular myopathy) or as part of Kearns-Sayre syndrome. Biochemical studies have documented either muscle-specific or generalized defects of COX; COX deficiency is reversible in the benign infantile myopathy. Immunologically detectable protein may be normal (benign myopathy) or variably decreased (fatal myopathy, Leigh syndrome). The subunit pattern of COX is normal by immunoblot in patients with fatal myopathy and Leigh syndrome; a disproportionate decrease of subunit II was seen in a patient with myoclonic epilepsy with ragged red fibers. Availability of the three mtDNA genes and of complementary DNA probes for eight of the 10 nuclear DNA-encoded subunits makes it possible to investigate the different diseases at the molecular level. Large deletions of mtDNA have been found in patients with ocular myopathy and Kearns-Sayre syndrome: the deleted mtDNA appear to be transcribed but not translated, thus explaining the partial COX deficiency.

Differential diagnosis of fatal and benign cytochrome c oxidase-deficient myopathies of infancy: an immunohistochemical approach

To differentiate the 2 major myopathies of infancy due to cytochrome c oxidase (COX) deficiency, we studied muscle biopsies from 4 patients with fatal myopathy and 4 with benign myopathy using biochemical, histochemical, and immunohistochemical techniques. Immunohistochemistry with antibodies directed against individual subunits of COX differentiated the 2 phenotypes: the fatal infantile myopathy was characterized by absence of the nuclear DNA (nDNA)-encoded subunit VIIa,b of COX, while in the benign myopathy both VIIa,b and the mitochondrial DNA (mtDNA)-encoded subunit II were absent. Early differential diagnosis between fatal and benign COX-deficient myopathies is of critical importance for prognosis and management of these infants, because the benign form is initially life-threatening but ultimately reversible.

Decreased antioxidant defence in individuals infected by the human immunodeficiency virus

BACKGROUND

The oxidative stress associated with HIV infection may be important for the progression of the disease because reactive oxygen species activate the nuclear transcription factor NF-kappaB, which is obligatory for HIV replication.

PATIENTS AND METHODS

The activities of the antioxidant enzymes superoxide dismutase (SOD, EC 1.15.1.1) and glutathione peroxidase (GPx, EC 1.11.1.9) of blood plasma and peripheral blood mononuclear cells, as well as the plasma levels of ascorbate, alpha-tocopherol and beta-carotene, were measured in 75 subjects with HIV infection and in 26 controls. The HIV-infected patients were classified according to the Walter Reed Army Institute criteria.

RESULTS

The extracellular SOD (EC-SOD) of blood plasma activity was decreased in HIV-infected patients compared to controls, while the SOD activity of mononuclear cells decreased with the HIV-associated disease progression. GPx activities and alpha-tocopherol concentration of HIV-infected patients neither differed as compared to controls nor in relation to disease progression. Lower concentrations of ascorbate and beta-carotene were found in HIV-infected patients than in controls. A positive correlation between CD4 lymphocyte counts and the SOD activities of plasma and mononuclear cells was found.

CONCLUSION

These results suggest that abnormalities of antioxidant defence, mainly of SOD activity, are related to the progression of the HIV infection.

Modulation of striatal quinolinate neurotoxicity by elevation of endogenous brain kynurenic acid

1. Nicotinylalanine, an inhibitor of kynurenine metabolism, has been shown to elevate brain levels of endogenous kynurenic acid, an excitatory amino acid receptor antagonist. This study examined the potential of nicotinylalanine to influence excitotoxic damage to striatal NADPH diaphorase (NADPH-d) and gamma-aminobutyric acid (GABA)ergic neurones that are selectively lost in Huntington's disease. 2. A unilateral injection of the N-methyl-D-aspartate (NMDA) receptor agonist, quinolinic acid, into the rat striatum produced an 88% depletion of NADPH-d neurones. Intrastriatal infusion of quinolinic acid also produced a dose-dependent reduction in striatal GABA content. 3. Nicotinylalanine (2.3, 3.2, 4.6, 6.4 nmol 5 microl(-1), i.c.v.) administered with L-kynurenine (450 mg kg(-1)), a precursor of kynurenic acid, and probenecid (200 mg kg(-1)), an inhibitor of organic acid transport, 3 h before the injection of quinolinic acid (15 nmol) produced a dose-related attenuation of the quinolinic acid-induced loss of NADPH-d neurones. Nicotinylalanine (5.6 nmol 5 microl(-1)) in combination with L-kynurenine and probenecid also attenuated quinolinic acid-induced reductions in striatal GABA content. 4. Nicotinylalanine (4.6 nmol, i.c.v.), L-kynurenine alone or L-kynurenine administered with probenecid did not attenuate quinolinic acid-induced depletion of striatal NADPH-d neurones. However, combined administration of kynurenine and probenecid did prevent quinolinic acid-induced reductions in ipsilateral striatal GABA content. 5. Injection of nicotinylalanine, at doses (4.6 nmol and 5.6 nmol i.c.v.) which attenuated quinolinic acid-induced striatal neurotoxicity, when combined with L-kynurenine and probenecid produced increases in both whole brain and striatal kynurenic acid levels. Administration of L-kynurenine and probenecid without nicotinylalanine also elevated kynurenic acid, but to a lesser extent. 6. The results of this study demonstrate that nicotinylalanine has the potential to attenuate quinolinic acid-induced striatal neurotoxicity. It is suggested that nicotinylalanine exerts its effect by increasing levels of endogenous kynurenic acid in the brain. The results of this study suggest that agents which influence levels of endogenous excitatory amino acid antagonists such as kynurenic acid may be useful in preventing excitotoxic damage to neurones in the CNS.

Heteroplasmy of mitochondrial genomes in clonal cultures from patients with Kearns-Sayre syndrome

We have analyzed heteroplasmy of mitochondrial DNA in clonal cultures from two patients with Kearns-Sayre syndrome, and have found that individual muscle or fibroblast clones contained either a mixed (i.e. heteroplasmic) population of normal and deleted mitochondrial DNAs, or only normal mitochondrial DNAs (i.e. homoplasmic at a level of detection of less than 1% deleted genomes). The heteroplasmic clones grew significantly more slowly than did "homoplasmic" clones, probably due to defects of respiratory chain enzymes containing mtDNA-encoded polypeptides.

Phosphoglycerate kinase deficiency: another cause of recurrent myoglobinuria

A 14-year-old boy had myoglobinuria and renal failure after intense exercise; a year earlier he had experienced a milder episode. There was no consanguinity and no family history of neuromuscular diseases or hemolytic anemia. Strength was normal. Forearm ischemic exercise caused prolonged contracture with no rise of venous lactate. Muscle morphology showed only a mild increase of lipid droplets. Glycogen concentration was normal. Muscle phosphoglycerate kinase (PGK) activity was 5% of the normal mean, and all other glycolytic enzymes were normal. The residual PGK activity of muscle was heat stable but showed slower than normal electrophoretic mobility and decreased Michaelis constants for 3-phosphoglycerate and adenosine triphosphate. The enzyme defect was also expressed in erythrocytes and in fibroblast and muscle cultures. PGK activity was decreased in tissues from the patient's mother but normal in the father. PGK deficiency is an X-linked recessive trait usually associated with hemolytic anemia, mental retardation, and seizures; myopathy had not been recognized previously. Muscle PGK deficiency is now added to two other newly recognized glycolytic defects, phosphoglycerate mutase and lactate dehydrogenase deficiencies, as a cause of recurrent myoglobinuria.

Applications of microalgal biofilms for wastewater treatment and bioenergy production

BACKGROUND

Microalgae have shown clear advantages for the production of biofuels compared with energy crops. Apart from their high growth rates and substantial lipid/triacylglycerol yields, microalgae can grow in wastewaters (animal, municipal and mining wastewaters) efficiently removing their primary nutrients (C, N, and P), heavy metals and micropollutants, and they do not compete with crops for arable lands. However, fundamental barriers to the industrial application of microalgae for biofuel production still include high costs of removing the algae from the water and the water from the algae which can account for up to 30-40% of the total cost of biodiesel production. Algal biofilms are becoming increasingly popular as a strategy for the concentration of microalgae, making harvesting/dewatering easier and cheaper.

RESULTS

We have isolated and characterized a number of natural microalgal biofilms from freshwater, saline lakes and marine habitats. Structurally, these biofilms represent complex consortia of unicellular and multicellular, photosynthetic and heterotrophic inhabitants, such as cyanobacteria, microalgae, diatoms, bacteria, and fungi. Biofilm #52 was used as feedstock for bioenergy production. Dark fermentation of its biomass by Enterobacter cloacae DT-1 led to the production of 2.4 mol of H₂/mol of reduced sugar. The levels and compositions of saturated, monosaturated and polyunsaturated fatty acids in Biofilm #52 were target-wise modified through the promotion of the growth of selected individual photosynthetic inhabitants. Photosynthetic components isolated from different biofilms were used for tailoring of novel biofilms designed for (i) treatment of specific types of wastewaters, such as reverse osmosis concentrate, (ii) compositions of total fatty acids with a new degree of unsaturation and (iii) bio-flocculation and concentration of commercial microalgal cells. Treatment of different types of wastewaters with biofilms showed a reduction in the concentrations of key nutrients, such as phosphates, ammonia, nitrates, selenium and heavy metals.

CONCLUSIONS

This multidisciplinary study showed the new potential of natural biofilms, their individual photosynthetic inhabitants and assembled new algal/cyanobacterial biofilms as the next generation of bioenergy feedstocks which can grow using wastewaters as a cheap source of key nutrients.

Cytochrome c oxidase deficiency in Leigh's syndrome: genetic evidence for a nuclear DNA-encoded mutation

Although an apparently generalized defect of cytochrome c oxidase (COX) occurs in many patients with subacute necrotizing encephalomyelopathy (Leigh's syndrome), the mode of inheritance in this disorder is not known. We transformed COX-deficient fibroblasts from a child with Leigh's syndrome with simian virus 40 to obtain cells with an infinite life span. These cells were still COX-deficient, grew normally in HAT medium, and were ouabain-sensitive. We fused these cells with a HAT-sensitive, ouabain-resistant variant of HeLa cells (HeLacot) and isolated surviving hybrid clones in ouabain-containing HAT medium. Prolonged cultivation of the hybrids was accompanied by preferential loss of HeLacot mitochondrial DNA (mtDNA), as determined by mtDNA restriction patterns of parental and hybrid cell DNA with the restriction endonuclease HaeII. COX activity was normal or higher than normal in hybrids, including the progeny of cell clones that had lost almost all the HeLacot mtDNA. These data demonstrate that COX deficiency in this Leigh's syndrome patient's cells was corrected by a nuclear DNA-encoded factor from the HeLacot parent and ruled out an mtDNA mutation as the basis for COX deficiency. This system can be used to determine whether different generalized mitochondrial disorders are due to mutations of nuclear or mtDNA.

Multiple mtDNA deletions features in autosomal dominant and recessive diseases suggest distinct pathogeneses

Multiple mitochondrial DNA (mtDNA) deletions have been described in patients with autosomal dominant progressive external ophthalmoplegia (AD-PEO) and in autosomal recessive disorders including mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and autosomal recessive cardiomyopathy ophthalmoplegia (ARCO). The pathogenic bases of these disorders are unknown. We studied three patients with AD-PEO and three patients with autosomal recessive (AR)-PEO (two patients with MNGIE and one patient with ARCO). Histochemistry and Southern blot analyses of DNA were performed in skeletal muscle from the patients. Muscle mtDNA was used to characterize the pattern and amounts of the multiple mtDNA rearrangements; PCR analysis was performed to obtain finer maps of the deleted regions in both conditions. The patients with AD-PEO had myopathic features; the patients with AR-PEO had multisystem disorders. The percentage of ragged-red and cytochrome c oxidase-negative fibers tended to be higher in muscle from the patients with AD-PEO (19% +/- 13.9, 29.7 +/- 26.3) than in muscle from the patients with AR-PEO (1.4% +/- 1.4, 3.3% +/- 3.2; p < 0.10). The sizes of the multiple mtDNA deletions ranged from approximately 4.0 to 10.0 kilobases in muscle from both groups of patients, and in both groups, we identified only deleted and no duplicated mtDNA molecules. Patients with AD-PEO harbored a greater proportion of deleted mtDNA species in muscle (31% +/- 5.3) than did patients with AR-PEO (9.7% +/- 9.1; p < 0.05). In the patients with AD-PEO, we identified a deletion that included the mtDNA heavy strand promoter (HSP) region, which had been previously described as the HSP deletion. The HSP deletion was not present in the patients with AR-PEO. Our findings show the clinical, histologic, and molecular genetic heterogeneity of these complex disorders. In particular, the proportions of multiple mtDNA deletions were higher in muscle samples from patients with AD-PEO than in those from patients with AR-PEO.

Myoadenylate deaminase deficiency--muscle biopsy and muscle culture in a patient with gout

AMP deaminase activity was undetectable by a sensitive spectrophotometric assay in the muscle biopsy of a 37-year-old man with gout and exercise-related cramps and myalgia. Venous ammonia failed to rise after ischemic exercise, but the diagnostic value of this test is uncertain because changes of plasma ammonia after exercise varied greatly in different normal individuals. In the patient, AMP deaminase activity was normal not only in erythrocytes, leukocytes and cultured fibroblasts but also in muscle cultures. Presence of AMP deaminase in muscle cultures was probably due to the expression of a fetal isoenzyme under separate genetic control from adult muscle AMP deaminase.

Muscle phosphoglycerate mutase deficiency

A 52-year-old man complained since adolescence of cramps and pigmenturia after 15 to 30 minutes of intense exercise. There was no family history of neuromuscular diseases, and strength was normal. The rise of venous lactate after forearm ischemic exercise was abnormally low. Histochemical and ultrastructural studies of a muscle biopsy showed mild increase of glycogen, which was confirmed by biochemical analysis. Studies of anaerobic glycolysis in vitro showed decrease lactate formation with glycogen and with all hexosephosphate glycolytic intermediates, suggesting a defect below the phosphofructokinase reaction. Muscle phosphoglycerate mutase (PGAM) activity was 5.7% of the lowest control, while all other enzymes of glycolysis had normal activities. Electrophoretic, heat lability, and mercury inhibition studies showed that the small residual activity of PGAM in the patient's muscle was represented by the brain (BB) isoenzyme, suggesting a genetic defect of the M subunit that predominates in normal muscle. The prevalence of the BB isoenzyme in other tissues, including muscle culture, may explain why symptoms were confined to muscle.

Heterogeneity of the molecular lesions in inherited phosphofructokinase deficiency

Human phosphofructokinase (PFK; EC 2.7.1.11) exists in tetrameric isozymic forms. Muscle and liver contain the homotetramers M4 and L4, whereas erythrocytes contain five isozymes composed of M (muscle) and L (liver) subunits, i.e., M4, M3L, M2L2, ML3, and L4. Inherited defects of erythrocyte PFK are usually partial and are described in association with heterogeneous clinical syndromes. To define the molecular basis and pathogenesis of this enzymopathy, we investigated four unrelated individuals manifesting myopathy and hemolysis (glycogenosis type VII), isolated hemolysis, or no symptoms at all. The three symptomatic patients showed high-normal hemoglobin levels, despite hemolysis and early-onset hyperuricemia. They showed total lack of muscle-type PFK and suffered from exertional myopathy of varying severity. In the erythrocytes, a metabolic crossover was evident at the PFK step: the levels of hexose monophosphates were elevated and those of 2,3-diphosphoglycerate (2,3-DPG) were depressed, causing strikingly increased hemoglobin-oxygen affinity. In all cases, the residual erythrocyte PFK consisted exclusively of L4 isozyme, indicating homozygosity for the deficiency of the catalytically active M subunit. However, presence of immunoreactive M subunit was shown in cultured fibroblasts by indirect immunofluorescence with monoclonal anti-M antibody. The fourth individual was completely asymptomatic, had normal erythrocyte metabolism, and had no evidence of hemolysis. His residual erythrocyte PFK showed a striking decrease of the L4, ML3, and M2L2 isozymes, secondary to a mutant unstable L subunit. Identical alterations of erythrocyte PFK were found in his asymptomatic son, indicating heterozygosity for the mutant unstable L subunit in this kindred. These studies show that, except for the varying severity of the myopathic symptoms, glycogenosis type VII has highly uniform clinical and biochemical features and results from homozygosity for mutant inactive M subunit(s). The absence of anemia despite hemolysis may be explained by the low 2,3-DPG levels. The hyperuricemia may result from hyperactivity of the hexose monophosphate shunt. In contrast, the clinically silent carrier state results from heterozygosity for mutant M or L subunit. Of the two, the M subunit appears to be more critical for adequate glycolytic flux in the erythrocyte, since its absence is correlated with hemolysis.