Biomedical subjects

N G Larsson

Publications and source records attributed to N G Larsson.

At least 37 records · Page 2Linked to original sources

PubMed1995

Inheritance and expression of mitochondrial DNA point mutations.

An important feature of the mitochondrial genom is the occurrence of heteroplasmy and the possibility for transmission to the offspring of various proportions of wild-type and mutated mtDNA. We have investigated the proportion of the tRNALys A8344G mutation, the tRNALeu(UUR) A3243G mutation, and the ATPase 6 T8993G mutation in patients with MERRF, MELAS, and Leigh's syndrome and their maternal relatives. The level of mutated mtDNA in the offspring of carriers of the tRNALys mutation is correlated to the level in lymphocytes in the mother and seems to be transmitted by an essentially random mechanism where only a few mtDNA copies are founders of the mitochondrial genom in the offspring and the probability that the mutation is not transmitted to the offspring is high when the mothers carriers predominantly wild-type mtDNA. However, we found age-related differences in the distribution of mutated mtDNA in carriers of the tRNALys and tRNALeu mutations, which have to be considered before levels of mutated mtDNA are used for prediction of prognosis and transmission of a disorder.

Adolescent↗

PubMed1995

Pathogenetic aspects of the A8344G mutation of mitochondrial DNA associated with MERRF syndrome and multiple symmetric lipomas.

Myoclonus epilepsy and ragged-red fibers syndrome (MERRF) is caused by a heteroplasmic mutation at nucleotide 8344 (A8344G) of the tRNA(Lys) gene of mitochondrial DNA (mtDNA). This mutation impairs mitochondrial protein synthesis and causes a respiratory chain dysfunction. The risk for transmission of the A8344G mutation from mother to child is dependent on the levels of mutated mtDNA in the mother and above a threshold level of 35-40% the mutation is transmitted to all children. The progression of symptoms in MERRF can be explained by a gene dosage effect with accumulation over time of mutated mtDNA. High levels of mutated mtDNA, ultrastructurally abnormal mitochondria, and a clonal deletion on chromosome 6 are found in lipomas associated with MERRF. These findings indicate that there is a respiratory chain dysfunction in the lipomas and that lipomas may be a manifestation of the A8344G mutation.

Child↗

PubMed1995

De novo mutation in the mitochondrial ATP synthase subunit 6 gene (T8993G) with rapid segregation resulting in Leigh syndrome in the offspring.

The mutation in the mitochondrial ATP synthase subunit 6 gene (ATP6 T8993G) was identified in a male infant who died at age 15 months of Leigh syndrome. He had 94% mutated mitochondrial DNA (mtDNA) in muscle and 92% in lymphocytes. His mother was healthy but had 37% mutated mtDNA in muscle and 38% in lymphocytes. The proband's brother, who was also healthy, had 44% mutated mtDNA in lymphocytes. No mutated mtDNA was detected in muscle and lymphocytes from the maternal grandmother of the proband or in lymphocytes from 15 other maternal relatives, showing that the first carrier of the ATP6 T8993G mutation in this family was the mother of the proband. This study shows that this point mutation may occur at substantial levels in a carrier of a de novo mutation and rapid segregation with high levels of mutated mtDNA causing neurodegenerative disease may occur in the second generation.

2,4-Dinitrophenol↗

PubMed1995

Tissue distribution and disease manifestations of the tRNA(Lys) A-->G(8344) mitochondrial DNA mutation in a case of myoclonus epilepsy and ragged red fibres.

This man with myoclonus epilepsy and ragged red fibres (MERRF) syndrome due to the tRNA(Lys) A-->G(8344) mutation of mitochondrial DNA (mtDNA) died of bronchopneumonia at 18 years of age. He had progressive clinical symptoms from 6 months of age manifesting as ataxia, myoclonic seizures, and muscle weakness. A post-mortem examination revealed 91-99% mutated mtDNA in all 32 examined tissue samples, including various organs and different brain regions. The brain appeared without macroscopic changes, but microscopic examination showed degeneration with loss of nerve cells and gliosis affecting the globus pallidus, substantia nigra, red nucleus, dentate nucleus, inferior olivary nucleus, cerebellar cortex, and the spinal cord. Skeletal muscle showed cytochrome c oxidase deficient muscle fibres with proliferation of mitochondria. In addition to pathological changes of muscle and brain there were few morphological changes that could be attributed to his mitochondrial disease. These data support the concept that in patients with the tRNA(Lys) A-->G(8344) mutation who are manifesting disease there are high levels of mutated mtDNA in all tissues, but only some tissues and brain regions are vulnerable.

Adolescent↗

PubMed1995

Atypical presentation of multisystem disorders in two girls with mitochondrial DNA deletions.

UNLABELLED: We describe two girls with atypical presentations of multisystem disorders due to deletions in mitochondrial DNA (mtDNA). One presented with painful carpopedal spasms due to hypoparathyroidism at the age of 4 years. The disease was rapidly progressive with development of truncal and limb ataxia, spastic paraparesis, muscle weakness and wasting, pigmentary retinal degeneration and sensorineural hearing loss. She had short stature and vitiligo patches, hirsutism, anaemia, diabetes mellitus and exocrine pancreatic dysfunction. The other girl presented at the age of 6 years with polydipsia, polyuria and fatigue due to renal tubular dysfunction. The disease was insidiously progressive with poor growth and development of sensorineural hearing loss, muscle weakness and truncal and limb ataxia. Morphological, enzyme histochemical and biochemical investigations indicated mitochondrial dysfunction of skeletal muscle, liver and kidney in one patient and of skeletal muscle and liver in the other. Both patients had large proportions of mtDNA molecules with deletion in liver, kidney, skeletal muscle and blood cells. CONCLUSION: It may be concluded that symptoms from several different organs may be the first manifestation of a mtDNA deletion disorder.

Blotting, Southern↗

PubMed1995

Mitochondrial DNA deletions in muscle fibers in inclusion body myositis.

Inclusion body myositis (IBM) is an autoimmune, inflammatory myopathy where morphological changes of muscle, including ragged red fibers, have indicated mitochondrial dysfunction in some muscle fibers. In this study enzyme histochemical analysis showed that cytochrome c oxidase (COX)-deficient muscle fibers were present at a frequency ranging from 0.5 to 5% of the muscle fibers in a series of 20 IBM patients. In age-matched controls, only occasional COX-deficient muscle fibers were present. Polymerase chain reaction (PCR) analysis of DNA extracted from muscle tissue of the IBM patients showed multiple mtDNA deletions. PCR analysis of isolated, single muscle fibers showed presence of mtDNA with only one type of deletion and deficiency of wild-type mtDNA in each COX-deficient muscle fiber. This finding was supported by results from in situ hybridization using different mtDNA probes on consecutive sections. A 5 kb deletion was identified in all 20 IBM patients. DNA sequencing of the breakpoint region showed that this deletion was the so-called "common deletion." Most but not all of the investigated deletion breakpoints were flanked by direct repeats. COX-deficient fibers were more frequent among fibers with positive immunostaining with antibodies directed toward a regeneration marker, the Leu-19 antigen, than in the entire fiber population. These results show that COX deficiency in muscle fiber segments in IBM is associated with deletions of mtDNA. Clonal expansion of mtDNA with deletions may take place in regenerating muscle fibers following segmental necrosis.

Adult↗

PubMed1995

Use of primary cultures and continuous cell lines to study effects on astrocytic regulatory functions.

1. Current opinions on the mechanisms for glutamate-mediated neurotoxicity are reviewed. The protective role of astrocytic high-affinity glutamate transport is also discussed. 2. Low-density seeding of primary astrocytes from rat hemispheres was found to result in the development of reactive-like astrocytes. Typical glial signs of amyotrophic lateral sclerosis (ALS) could not be induced in astrocyte cultures by serum from ALS-patients. 3. Glutamate (100 mumol/L) was found to induce an increase in respiratory activity in primary cultures of astrocytes. This stimulation appeared to be related to the co-transport of Na2+ with glutamate and a resulting activation of Na2+/K(+)-ATPase. Both basal respiration and glutamate-stimulated oxygen consumption was inhibited by organic solvents. 4. Preliminary results show that heavy metals cause an increase in the mitochondrial DNA content at concentrations that have no effect on growth rate or morphology in a glial cell line. This increase was accompanied by an inhibition of oxygen consumption and an increased production of lactate at unaltered ATP levels.

Amyotrophic Lateral Sclerosis↗

PubMed1995

Molecular genetic aspects of human mitochondrial disorders.

This review focuses on mutations of mitochondrial DNA (mtDNA) which are an important cause of mitochondrial disorders in humans and are also associated with common neurodegenerative disorders and aging. The high copy number of mtDNA and its maternal transmission make the inheritance of mtDNA mutations fundamentally different from the Mendelian inheritance of nuclear DNA mutations. There is often a mixture of wild-type and mutated mtDNAs (heteroplasmy), and heterogeneity in the distribution of mutated mtDNAs is one plausible explanation for the widely varying phenotypes in patients with mitochondrial disorders. The application of molecular genetics has led to significant progress in the studies of human mitochondrial disorders in the past decade. Future studies including the development of animal models are needed to advance our understanding of the pathogenesis of mitochondrial disorders to enable, in turn, the development of novel therapies and genetic rescue strategies for the treatment of human disease.

Animals↗

PubMed1994

Low levels of mitochondrial transcription factor A in mitochondrial DNA depletion.

Low levels of mitochondrial transcription factor A (mtTFA) were found in muscle fibers with mitochondrial DNA (mtDNA) depletion in a child with fatal mitochondrial myopathy and also in a human cell line lacking mtDNA. High levels of this transcriptional activator were found in muscle fibers with mtDNA accumulation in two patients with single mtDNA deletions. This is the first example of a nuclear gene product that varies with the levels of mtDNA in humans. Since transcription is required for the replication of mtDNA, it is possible that mtTFA may be involved in the regulation of mtDNA replication.

Child, Preschool↗

PubMed1994

Automatic sequencing of mitochondrial tRNA genes in patients with mitochondrial encephalomyopathy.

We have investigated nine children with infantile onset of mitochondrial myopathy and two adults with myoclonus epilepsy and ragged-red fibers (MERRF) and chronic progressive external ophthalmoplegia (CPEO), respectively. These patients lacked any of the previously known pathogenic tRNA mutations. Southern blot analysis of muscle mtDNA revealed no deletions. The tRNA genes of muscle mtDNA were sequenced. Restriction enzyme analysis of PCR fragments was performed to verify the presence of the mutations identified by automatic sequencing. Several tRNA mutations were found, but they were all homoplasmic. Furthermore, the mutations were either present in controls or did not change nucleotides conserved between species. This strongly suggests that none of the tRNA mutations identified in the 11 patients with mitochondrial encephalomyopathy was pathogenic. It can thus be concluded that mitochondrial tRNA mutations and mtDNA deletions probably are an infrequent cause of mitochondrial disorders in infants. Patients with MERRF and CPEO may lack both pathogenic point mutations of tRNA genes and deletions of mtDNA.

Adult↗

PubMed1993

Mitochondrial DNA deletions in inclusion body myositis.

Skeletal muscle specimens from three patients with inclusion body myositis, aged 39, 60 and 71 years, respectively, were investigated. Enzyme histochemical staining of cytochrome c oxidase (COX), succinate dehydrogenase and myofibrillar ATPase, and in situ hybridization of transcripts of mitochondrial DNA (mtDNA) were performed on consecutive sections. In all three cases a proportion of muscle fibres (2-5%) showed low or absent COX activity in spite of medium or high succinate dehydrogenase activity (COX deficient muscle fibres). Two probes detecting transcripts of different segments of mtDNA were used for the in situ hybridization. One of the probes (ND4 probe) detected transcripts of a segment of the NADH dehydrogenase subunit 4 gene, which is known to be affected in most cases of mitochondrial myopathy with large deletions of mtDNA. There was reduced hybridization of the ND4 probe in many COX deficient muscle fibres compared with adjacent normal fibres. The other probe (ND2 probe) detected transcripts of a segment of the NADH dehydrogenase subunit 2 gene, which usually is not included in mtDNA deletions. There was accumulation of transcripts corresponding to the ND2 probe in COX deficient fibres in all three cases. These findings demonstrate that deleted mtDNA had accumulated in COX deficient muscle fibres in patients with inclusion body myositis. Southern blot analysis of mtDNA in muscle revealed a 16.6 kb fragment corresponding to normal mtDNA in all three cases. In one case two additional less abundant fragments of smaller size, corresponding to deleted mtDNA, were detected. Ultrastructural investigation showed abnormal mitochondria in all three cases. Control muscle specimens were obtained from nine patients, aged 63-71 years, with muscle pain but without morphological evidence of muscle disease. Occasional COX deficient fibres (< 1%) were found in three of the control cases. The other six control cases showed no COX deficient fibres. Our results show that mtDNA deletions may be involved in the pathogenesis of inclusion body myositis and cause respiratory chain dysfunction in muscle fibre segments.

Adult↗

PubMed1993

Multiple symmetric lipomas with high levels of mtDNA with the tRNA(Lys) A-->G(8344) mutation as the only manifestation of disease in a carrier of myoclonus epilepsy and ragged-red fibers (MERRF) syndrome.

We have investigated the morphology, cytogenetics, and the fraction of mtDNA with the tRNA(Lys) A-->G(8344) mutation in three lipomas in a carrier of this mutation. The son of the patient had myoclonus epilepsy and ragged-red fibers syndrome. The fraction of mtDNA with the tRNA(Lys) mutation varied between 62% and 80% in cultured skin fibroblasts, lymphocytes, normal adipose tissue, and muscle. In the three lipomas the mean fraction of mutated mtDNA was 90%, 94%, and 94%. Ultrastructural examination of the lipomas revealed numerous mitochondria with changes such as electron-dense inclusions in some adipocytes. When considered cytogenetically, the lipomas were characterized by a mixture of karyotypically abnormal and normal cells. An identical del(6)(q24) was found in two tumors. The fraction of mutated mtDNA in cultured lipoma cells was the same as in the lipoma in situ, indicating that the cultured cells were representative of the primary tumor. These findings indicate that the lipomas have originated with a grossly normal stem line and subsequently have developed the 6q deletion. We conclude that the lipomas represent clonal growth of adipocytes with a high content of mtDNA with the tRNA(Lys) mutation. The tRNA(Lys) mutation may be either the direct or the indirect cause of pertubation of the maturation process of the adipocytes, leading to an increased risk of lipoma formation.

Adenine↗

PubMed1992

Multiple short direct repeats associated with single mtDNA deletions.

We have sequenced the breakpoints of deleted mtDNA in muscle from four children with mitochondrial myopathy and multisystem mitochondrial disorders. The deletions were 4884, 6067, 7663 and 7150 base pairs (bp) in size and affected several protein and transfer RNA genes. The sequences needed for transcription and replication of mtDNA were not affected in any case. The deletions were flanked by direct short repeats in all cases. Multiple repeats were found in case 1 and 4. Imperfect repeats were found in case 3 and 4 and this made it possible to distinguish the repeats 5' and 3' to the deletion. In both cases the 3' repeat was retained. The deletion of 7663 bp in case 3 has been reported in two other cases and may represent a second hotspot for mtDNA deletions in addition to the common deletion of 4977 bp found in one third of cases. A comparison of the breakpoint sequence of case 3 with the two other reported cases revealed that when a deletion is formed between the same repeats in different patients either the 5' or 3' repeat can be retained. This study shows that both single and multiple repeats can be associated with single mtDNA deletions and that both 5' and 3' repeated sequences can be retained. These findings are consistent with the slip-replication model for the generation of mtDNA deletions.

Base Sequence↗

PubMed1992

Mitochondrial DNA deletions and cytochrome c oxidase deficiency in muscle fibres.

We have studied cytochrome c oxidase (COX) deficient muscle fibre segments in 6 patients with mitochondrial myopathy and deletions of mitochondrial DNA (mtDNA). The distribution of transcripts of normal and mutated mtDNA in skeletal muscle sections was studied by in situ hybridization. The results were compared with the enzyme histochemical activity of COX and the immunohistochemical distribution of mtDNA encoded and nuclear DNA encoded subunits of COX. In all cases a proportion of the muscle fibres (less than 1-30% of the fibres in cross-sections) had low COX activity and high activity of succinate dehydrogenase (COX deficient muscle fibres). Transcripts of normal and deleted mtDNA showed the same distribution within the tissue as the corresponding mtDNA, indicating that the deleted mtDNA is transcribed. The COX deficient muscle fibres showed accumulation of transcripts of deleted mtDNA, which had a similar distribution as the accumulated mitochondria within these fibres. With few exceptions, there was a low level of transcripts of normal mtDNA in these COX deficient fibres. Immunohistochemical analysis revealed low levels of immunoreactive material using antiserum to the mtDNA encoded subunits II/III as well as the nuclear DNA encoded subunit IV of COX in all COX deficient muscle fibres. The fraction of deleted mtDNA in muscle ranged from 43 to 87%. There was no correlation between the proportion of COX deficient muscle fibres and the fraction of deleted mtDNA. In 2 cases the deletion did not involve any COX gene. One of these cases had 87% deleted mtDNA but less than 1% COX deficient muscle fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1992

Mitochondrial ATP-synthase deficiency in a child with 3-methylglutaconic aciduria.

We report the finding of mitochondrial ATP-synthase deficiency in a child with persistent 3-methylglutaconic aciduria. The child presented in the neonatal period with severe lactic acidosis, which was controlled by Na-HCO3 and glucose infusions. During the 1st y of life, there were several episodes of lactic acidosis precipitated by infections or prolonged intervals between meals. The excretion of lactate in urine was variable, but there was a persistent high excretion of 3-methylglutaconic acid. The activity of 3-methylglutaconyl-CoA hydratase in fibroblasts was normal. The child had a hypertrophic cardiomyopathy and magnetic resonance images revealed hypoplasia of corpus callosum. The gross motor and mental development was retarded, but there were no other neurologic signs. Investigation of muscle mitochondrial function at 1 y of age revealed a severe mitochondrial ATP-synthase deficiency (oligomycin-sensitive, dinitrophenol-stimulated Mg2+ ATPase activity: 27 nmol x min-1 x (mg protein)-1, control range 223-673 nmol x min-1 x (mg protein)-1. The mitochondrial respiratory rate was low and tightly coupled. The respiratory rate was normalized by the addition of an uncoupler. Low Mg2+ ATPase activity was also demonstrated by histochemical methods. Morphologic examination revealed ultrastructural abnormalities of mitochondria. There was no deletion of mitochondrial DNA. The sequences of the ATP synthase subunit genes of mitochondrial DNA were in accordance with published normal sequences.

Acidosis, Lactic↗

PubMed1992

Segregation and manifestations of the mtDNA tRNA(Lys) A-->G(8344) mutation of myoclonus epilepsy and ragged-red fibers (MERRF) syndrome.

We have studied the segregation and manifestations of the tRNA(Lys) A-->G(8344) mutation of mtDNA. Three unrelated patients with myoclonus epilepsy and ragged-red fibers (MERRF) syndrome were investigated, along with 30 of their maternal relatives. Mutated mtDNA was not always found in the offspring of women carrying the tRNA(Lys) mutation. Four women had 10%-33% of mutated mtDNA in lymphocytes, and no mutated mtDNA was found in 7 of their 14 investigated children. The presence of mutated mtDNA was excluded at a level of 3:1,000. Five women had a proportion of 43%-73% mutated mtDNA in lymphocytes, and mutated mtDNA was found in all their 12 investigated children. This suggests that the risk for transmission of mutated mtDNA to the offspring increases if high levels are present in the mother and that, above a threshold level of 35%-40%, it is very likely that transmission will occur to all children. The three patients with MERRF syndrome had, in muscle, both 94%-96% mutated mtDNA and biochemical and histochemical evidence of a respiratory-chain dysfunction. Four relatives had a proportion of 61%-92% mutated mtDNA in muscle, and biochemical measurements showed a normal respiratory-chain function in muscle in all cases. These findings suggest that > 92% of mtDNA with the tRNA(Lys) mutation in muscle is required to cause a respiratory-chain dysfunction that can be detected by biochemical methods. There was a positive correlation between the levels of mtDNA with the tRNA(Lys) mutation in lymphocytes and the levels in muscle, in all nine investigated cases. The levels of mutated mtDNA were higher in muscle than in lymphocytes in all cases. In two of the patients with MERRF syndrome, muscle specimens were obtained at different times. In both cases, biochemical measurements revealed a deteriorating respiratory-chain function, and in one case a progressive increase in the amount of cytochrome c oxidase-deficient muscle fibers was found.

Adult↗

PubMed1992

Lack of transmission of deleted mtDNA from a woman with Kearns-Sayre syndrome to her child.

We have investigated the daughter of a woman with Kearns-Sayre syndrome. The woman had a high percentage of deleted mtDNA in muscle, but no deleted mtDNA was detected in fibroblasts, bone marrow, and peripheral blood cells by Southern blot analysis. With PCR, analytical sensitivity was significantly increased, and deleted mtDNA was detected in all examined tissues from this patient. The patient had healthy parents and nine healthy siblings. No deleted mtDNA was detected in blood from the mother of the patient. The patient had an uneventful pregnancy and delivered at term. Deleted mtDNA could not be detected in placenta by Southern blot analysis. With PCR, deleted mtDNA was detected in the majority of placental specimens. This finding may, however, be due to contamination with maternal DNA. The patient's daughter was healthy at age 5 mo, and morphologic examination of muscle was normal. No transmission of deleted mtDNA to the daughter could be detected by Southern blot and PCR analysis of peripheral blood cells, bone marrow, fibroblasts, and muscle. The presence of deleted mtDNA was excluded at a fractional level of less than 1:100,000 in all examined tissues from the daughter.

Adolescent↗

PubMed1991

Leber's hereditary optic neuropathy and complex I deficiency in muscle.

We investigated a family with Leber's hereditary optic neuropathy in which affected individuals were homoplasmic for the point mutation of the NADH-dehydrogenase 4 gene of mitochondrial DNA, described by Wallace and colleagues in 1988. The proband had bilateral optic atrophy, tremor, dystonia, and sharply defined lesions in the putamen on magnetic resonance images. Optic atrophy was found in another 3 of 13 investigated relatives on the maternal side. Additional neurological signs were found but only in patients with optic neuropathy. The morphological appearance and the respiratory chain function of muscle tissue were investigated in the proband, his mother, and 3 siblings. Polarographic measurements revealed complex I deficiency in the 5 investigated subjects. Morphological changes of mitochondria were found in 4 of these subjects. There was no decrease in complex I activity measured as NADH ferricyanide reductase or rotenone-sensitive NADH cytochrome c reductase activities. In other cases with complex I deficiency, good agreement between polarographic and spectrophotometric measurements was found. This study showed that there is decreased activity of complex I of the respiratory chain in muscle and that cerebral striatal lesions occur in Leber's hereditary optic neuropathy with the NADH-dehydrogenase 4 gene point mutation.

Adolescent↗