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Biomedical subjects

Michio Hirano

Publications and source records attributed to Michio Hirano.

At least 55 records · Page 3Linked to original sources
PubMed2004

MRI of five patients with mitochondrial neurogastrointestinal encephalomyopathy.

OBJECTIVE: The purpose of this study was to retrospectively review MR images of the brain in five patients diagnosed with mitochondrial neurogastrointestinal encephalomyopathy. CONCLUSION: Our research supports previously reported findings of confluent abnormal cerebral white matter in patients with mitochondrial neurogastrointestinal encephalomyopathy. In contrast to prior studies, our cohort of five patients showed that involvement of the corpus callosum as well as the capsular white matter, basal ganglia, thalami, midbrain, pons, and cerebellar white matter is not rare and does not preclude the diagnosis of mitochondrial neurogastrointestinal encephalomyopathy.

Adult↗
PubMed2003

Definitive diagnosis of mitochondrial neurogastrointestinal encephalomyopathy by biochemical assays.

BACKGROUND: Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by mutations in the gene encoding thymidine phosphorylase (TP). The clinical manifestations of MNGIE are recognizable and homogeneous, but in the early stages, the disease is often misdiagnosed. This study assesses the reliability of biochemical assays to diagnose MNGIE. METHODS: We studied 180 patients with clinical features suggestive of MNGIE, 14 asymptomatic TP mutation carriers, and 20 controls. TP enzyme activity in the buffy coat was determined by a fixed-time method, and the plasma nucleosides thymidine (dThd) and deoxyuridine (dUrd) were assessed by a gradient-elution reversed phase HPLC method. TP was sequenced through standard procedures in patients who met the clinical criteria for MNGIE. RESULTS: Twenty-five of the 180 patients fulfilled the clinical criteria for MNGIE and had homozygous or compound heterozygous TP mutations. All had drastically decreased TP activity [mean (SD), 10 (15) nmol thymine formed. h(-1). (mg protein)(-1) vs 634 (217) nmol thymine formed. h(-1). (mg protein)(-1) for the controls]. Relative to the control mean, TP activities were reduced to 35% in mutation carriers and 65% in MNGIE-like patients. All 25 MNGIE patients had detectable plasma dThd [8.6 (3.4) micromol/L] and dUrd [14.2 (4.4) micromol/L]. Controls, carriers, and MNGIE-like patients showed no detectable plasma dThd and dUrd. CONCLUSIONS: We propose a diagnostic algorithm based on the determination of plasma dThd and dUrd, TP activity in buffy coat, or both to make a definitive diagnosis of MNGIE. Increased concentrations of dThd (>3 micromol/L) and dUrd (>5 micromol/L) in plasma or a decrease in buffy coat TP activity to </=8% relative to controls is sufficient to diagnose MNGIE.

Chromatography, High Pressure Liquid↗
PubMed2003

ND5 is a hot-spot for multiple atypical mitochondrial DNA deletions in mitochondrial neurogastrointestinal encephalomyopathy.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive multisystem disorder associated with depletion, multiple deletions and site-specific point mutations of mitochondrial DNA (mtDNA). MNGIE is caused by loss-of-function mutations in the gene encoding thymidine phosphorylase (TP; endothelial cell growth factor 1). Deficiency of TP leads to dramatically elevated levels of circulating thymidine and deoxyuridine. The alterations of pyrimidine nucleoside metabolism are hypothesized to cause imbalances of mitochondrial nucleotide pools that, in turn, may cause somatic alterations of mtDNA. We have now identified five major forms of mtDNA deletions in the skeletal muscle of MNGIE patients. While direct repeats and imperfectly homologous sequences appear to mediate the formation of mtDNA deletions, the nicotinamide adenine dinucleotide dehydrogenase 5 gene is a hot-spot for these rearrangements. A novel aspect of the mtDNA deletions in MNGIE is the presence of microdeletions at the imperfectly homologous breakpoints.

Base Sequence↗
PubMed2003

A homoplasmic mitochondrial transfer ribonucleic acid mutation as a cause of maternally inherited hypertrophic cardiomyopathy.

OBJECTIVES: The purpose of this study was to understand the clinical and molecular features of familial hypertrophic cardiomyopathy (HCM) in which a mitochondrial abnormality was strongly suspected. BACKGROUND: Defects of the mitochondrial genome are responsible for a heterogeneous group of clinical disorders, including cardiomyopathy. The majority of pathogenic mutations are heteroplasmic, with mutated and wild-type mitochondrial deoxyribonucleic acid (mtDNA) coexisting within the same cell. Homoplasmic mutations (present in every copy of the genome within the cell) present a difficult challenge in terms of diagnosis and assigning pathogenicity, as human mtDNA is highly polymorphic. METHODS: A detailed clinical, histochemical, biochemical, and molecular genetic analysis was performed on two families with HCM to investigate the underlying mitochondrial defect. RESULTS: Cardiac tissue from an affected child in the presenting family exhibited severe deficiencies of mitochondrial respiratory chain enzymes, whereas histochemical and biochemical studies of the skeletal muscle were normal. Mitochondrial DNA sequencing revealed an A4300G transition in the mitochondrial transfer ribonucleic acid (tRNA)(Ile) gene, which was shown to be homoplasmic by polymerase chain reaction/restriction fragment length polymorphism analysis in all samples from affected individuals and other maternal relatives. In a second family, previously reported as heteroplasmic for this base substitution, the mutation has subsequently been shown to be homoplasmic. The pathogenic role for this mutation was confirmed by high-resolution Northern blot analysis of heart tissue from both families, revealing very low steady-state levels of the mature mitochondrial tRNA(Ile). CONCLUSIONS: This report documents, for the first time, that a homoplasmic mitochondrial tRNA mutation may cause maternally inherited HCM. It highlights the significant contribution that homoplasmic mitochondrial tRNA substitutions may play in the development of cardiac disease. A restriction of the biochemical defect to the affected tissue has important implications for the screening of patients with cardiomyopathy for mitochondrial disease.

Adolescent↗
PubMed2003

Elevated plasma deoxyuridine in patients with thymidine phosphorylase deficiency.

Mutations in the nuclear gene encoding thymidine phosphorylase (TP) cause mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), an autosomal recessive disease with mitochondrial dysfunction and mitochondrial DNA abnormalities. We have demonstrated alterations of thymidine (dThd) metabolism in MNGIE patients. Here, we report the accumulation of another substrate of TP, deoxyuridine (dUrd), whose circulating levels ranged from 5.5 to 24.4 microM (average 14.2) in MNGIE and were undetectable (<0.05 microM) in both TP mutation carriers and controls. The dramatic accumulation of dUrd may contribute to nucleotide pool imbalances and, together with the increased levels of dThd, is likely to contribute to the pathogenesis of MNGIE.

Base Sequence↗
PubMed2003

Mitochondrial myopathy of childhood associated with mitochondrial DNA depletion and a homozygous mutation (T77M) in the TK2 gene.

BACKGROUND: The mitochondrial DNA depletion syndrome is an autosomal recessive disorder of infancy or childhood characterized by decreased mitochondrial DNA copy number in affected tissues. Mutations in 2 genes involved in deoxyribonucleotide metabolism, the deoxyguanosine kinase gene (DGK) and the thymidine kinase 2 gene (TK2), have been related to this syndrome. OBJECTIVE: To describe 3 siblings with the myopathic form of mitochondrial DNA depletion syndrome and a homozygous mutation in the TK2 gene. PATIENTS AND METHODS: These children developed normally until 12 to 16 months of age, when they started showing difficulty walking, which rapidly progressed to severe limb weakness. They died of respiratory failure between the ages of 23 and 40 months. Histochemical and biochemical studies of respiratory chain complexes were performed in muscle biopsy specimens. The whole coding region of the TK2 gene was sequenced. RESULTS: Muscle biopsy showed ragged-red cytochrome-c oxidase-negative fibers. All affected siblings had markedly decreased activities of respiratory chain complexes. Southern blot analysis showed severe reduction of the mitochondrial DNA-nuclear DNA ratio in muscle biopsy specimens from all patients, indicating 80% to 90% mitochondrial DNA depletion. Sequencing of the TK2 gene showed a homozygous C-->T transition at nucleotide 228 in exon 5, which changes a threonine to a methionine at position 77 (T77M). CONCLUSIONS: These results document the importance of screening the TK2 gene in patients with myopathic mitochondrial DNA depletion syndrome and confirm that exon 5 is a "hot spot" for TK2 mutations.

Blotting, Southern↗
PubMed2003

Clinical and genetic heterogeneity in progressive external ophthalmoplegia due to mutations in polymerase gamma.

BACKGROUND: The mendelian forms of progressive external ophthalmoplegia (PEO) associated with multiple mitochondrial DNA deletions are clinically heterogeneous disorders transmitted as dominant or recessive traits. Autosomal dominant PEO is caused by mutations in at least 3 genes: adenine nucleotide translocator-1 (ANT1), encoding the muscle-specific adenine nucleotide translocator; chromosome 10 open reading frame 2 (C10orf2), encoding Twinkle helicase; and polymerase gamma (POLG), encoding the alpha subunit of polymerase gamma. Mutations in POLG can also cause autosomal recessive PEO, which is often associated with multisystemic disorders. OBJECTIVE AND METHODS: To further investigate the frequency and genotype-phenotype correlations of mutations in the POLG gene, we used single-stranded conformational polymorphism analysis and direct sequencing to screen 30 patients with familial or sporadic PEO and multiple mitochondrial DNA deletions in muscle but without mutations in ANT1 and C10orf2. RESULTS: Four unrelated patients had novel POLG mutations. A woman with PEO and mental retardation had a heterozygous Gly1076Val mutation. Two patients, one with PEO, exercise intolerance, and gastrointestinal dysmotility and the other with PEO, neuropathy, deafness, and hypogonadism, both had a Pro587Leu change. The fourth patient, who was compound heterozygous for Ala889Thr and Arg579Trp mutations, had PEO, gastrointestinal dysmotility, and neuropathy. These mutations were not detected in 120 healthy control alleles. CONCLUSIONS: Our results demonstrate that POLG mutations account for a substantial proportion of patients (13%) with PEO and multiple mitochondrial DNA deletions and cause both clinically and genetically heterogeneous disorders.

Adult↗
PubMed2003

Lack of paternal inheritance of muscle mitochondrial DNA in sporadic mitochondrial myopathies.

In 2002, paternal inheritance of muscle mitochondrial DNA (mtDNA) was reported in a patient with exercise intolerance and a mitochondrial DNA (mtDNA) mutation restricted to skeletal muscle. To evaluate whether paternal inheritance is a common phenomenon, we studied 10 sporadic patients with skeletal muscle-restricted mtDNA mutations: five harbored mtDNA point mutations in protein-coding genes and five had single mtDNA deletions. We performed haplotype analysis and direct sequencing of the hypervariable regions 1 and 2 of the D-loop in muscle and blood from the patients and, when available, in blood from their parents. We did not observe paternal inheritance in any of our patients.

DNA Mutational Analysis↗
PubMed2003

Primary coenzyme Q10 deficiency and the brain.

Our findings in 19 new patients with cerebellar ataxia establish the existence of an ataxic syndrome due to primary CoQ10 deficiency and responsive to CoQ10 therapy. As all patients presented cerebellar ataxia and cerebellar atrophy, this suggests a selective vulnerability of the cerebellum to CoQ10 deficiency. We investigated the regional distribution of coenzyme Q10 in the brain of adult rats and in the brain of one human subject. We also evaluated the levels of coenzyme Q9 (CoQ9) and CoQ10 in different brain regions and in visceral tissues of rats before and after oral administration of CoQ10. Our results show that in rats, amongst the seven brain regions studied, cerebellum contains the lowest level of CoQ. However, the relative proportion of CoQ10 was the same (about 30% of total CoQ) in all regions studied. The level of CoQ10 is much higher in brain than in blood or visceral tissue, such as liver, heart, or kidney. Daily oral administration of CoQ10 led to substantial increases of CoQ10 concentrations only in blood and liver. Of the four regions of one human brain studied, cerebellum again had the lowest CoQ10y concentration.

Animals↗
PubMed2003

A novel mitochondrial tRNA(Leu(UUR)) mutation in a patient with features of MERRF and Kearns-Sayre syndrome.

In a patient with clinical features of both myoclonus epilepsy ragged-red fibers (MERRF) and Kearns-Sayre syndrome (KSS), we identified a novel guanine-to-adenine mitochondrial DNA (mtDNA) mutation at nucleotide 3255 (G3255A) of the tRNA(Leu(UUR)) gene. Approximately 5% of the skeletal muscle fibers had excessive mitochondria by succinate dehydrogenase histochemistry while a smaller proportion showed cytochrome c oxidase (COX) deficiency. In skeletal muscle, activities of mitochondrial respiratory chain complexes I, I + III, II + III, and IV were reduced. The G3255A transition was heteroplasmic in all tissues tested: muscle (53%), urine sediment (67%), peripheral leukocytes (22%), and cultured skin fibroblasts (< 2%). The mutation was absent in 50 control DNA samples. Single-fiber analysis revealed a higher proportion of mutation in COX-deficient RRF (94% +/- 5, n = 25) compared to COX-positive non-RRF (18% +/- 9, n = 21). The identification of yet another tRNA(Leu(UUR)) mutation reinforces the concept that this gene is a hot-spot for pathogenic mtDNA mutations.

Adenine↗
PubMed2003

Characterization of Danon disease in a male patient and his affected mother.

Danon disease, primary lysosome-associated membrane protein-2 (LAMP-2) deficiency, is histologically characterized by unusual vacuoles bound by membranes with sarcolemmal features in skeletal muscle. We studied skeletal muscle specimens from a male patient with genetically confirmed Danon disease who had two muscle biopsies, at age 20 months and 16 years, and from his mother with cardiomyopathy but without clinically apparent skeletal myopathy. In the patient, the number of vacuoles increased over the 14-year interval between biopsies, suggesting that the number of vacuolated fibers increases with age, and correlates with the development of muscle symptoms. In contrast, in the muscle biopsy from the mother there were no vacuoles even though she had decreased LAMP-2.

Adolescent↗
PubMed2003

Site-specific somatic mitochondrial DNA point mutations in patients with thymidine phosphorylase deficiency.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder caused by loss-of-function mutations in the gene encoding thymidine phosphorylase (TP). This deficiency of TP leads to increased circulating levels of thymidine (deoxythymidine, dThd) and deoxyuridine (dUrd) and has been associated with multiple deletions and depletion of mitochondrial DNA (mtDNA). Here we describe 36 point mutations in mtDNA of tissues and cultured cells from MNGIE patients. Thirty-one mtDNA point mutations (86%) were T-to-C transitions, and of these, 25 were preceded by 5'-AA sequences. In addition, we identified a single base-pair mtDNA deletion and a TT-to-AA mutation. Next-nucleotide effects and dislocation mutagenesis may contribute to the formation of these mutations. These results provide the first demonstration that alterations of nucleoside metabolism can induce multiple sequence-specific point mutations in humans. We hypothesize that, in patients with TP deficiency, increased levels of dThd and dUrd cause mitochondrial nucleotide pool imbalances, which, in turn, lead to mtDNA abnormalities including site-specific point mutations.

Base Sequence↗
PubMed2003

Alteration of nucleotide metabolism: a new mechanism for mitochondrial disorders.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease caused by loss-of-function mutations in the gene encoding thymidine phosphorylase (TP). TP deficiency alters the metabolism of the nucleosides thymidine and deoxyuridine, which, in turn, produces abnormalities of mitochondrial DNA (mtDNA) including depletion, deletions, and point mutations. MNGIE is the best characterized of the expanding number of mitochondrial disorders caused by alterations in the metabolism of nucleosides/nucleotides. Because mitochondria contain their own machinery for nucleoside and nucleotide metabolism and have physically separate nucleotide pools, it is not surprising that disorders of these pathways cause human diseases. Other diseases in this group include mtDNA depletion syndromes caused by mutations on the nuclear genes encoding the mitochondrial thymidine kinase and deoxyguanosine kinase; autosomal dominant progressive external ophthalmoplegia with multiple deletions of mtDNA due to mutations in the genes encoding the muscle-isoform of mitochondrial ADP/ATP translocator; and mitochondrial DNA depletion due to toxicities of nucleoside analogues. Mutations in the deoxynucleotide carrier, a transporter of deoxynucleoside diphosphates, have been identified as a cause of congenital microcephaly. However, alterations of mtDNA have not yet been established in this disorder. Future studies are likely to reveal additional diseases and provide further insight into this new subject.

DNA, Mitochondrial↗
PubMed2002

Identical mitochondrial DNA deletion in a woman with ocular myopathy and in her son with pearson syndrome.

Single deletions of mitochondrial DNA (mtDNA) are associated with three major clinical conditions: Kearns-Sayre syndrome, a multisystem disorder; Pearson syndrome (PS), a disorder of the hematopoietic system; and progressive external ophthalmoplegia (PEO), primarily affecting the ocular muscles. Typically, single mtDNA deletions are sporadic events, since the mothers, siblings, and offspring of affected individuals are unaffected. We studied a woman who presented with PEO, ptosis, and weakness of pharyngeal, facial, neck, and limb muscles. She had two unaffected children, but another of her children, an infant son, had sideroblastic anemia, was diagnosed with PS, and died at age 1 year. Morphological analysis of a muscle biopsy sample from the mother showed cytochrome c oxidase-negative ragged-red fibers-a typical pattern in patients with mtDNA deletions. Southern blot analysis using multiple restriction endonucleases and probed with multiple mtDNA fragments showed that both the mother and her infant son harbored an identical 5,355-bp single deletion in mtDNA, without flanking direct repeats. The deletion was the only abnormal species of mtDNA identified in both patients, and there was no evidence for duplications. We conclude that, although the vast majority of single large-scale deletions in mtDNA are sporadic, in rare cases, single deletions can be transmitted through the germline.

Adolescent↗