Yu-ichi Goto

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke‐like episodes (MELAS): A correlative study of the clinical features and mitochondrial DNA mutation

We studied 40 MELAS patients (21 male and 19 female) to characterize the clinical features and biochemical and muscle biopsy findings related to the mtDNA mutation at the nucleotide position of 3,243, the most common genetic defect in MELAS. The most frequent symptom was episodic sudden headache with vomiting and convulsions, which commonly affected patients aged 5 to 15 years (80%). Biochemical defects in the muscle were variable; 13 patients had complex I, seven complex IV, and four complexes I+IV deficiencies. In four muscle biopsies without ragged-red fibers or any enzyme defect, we based the diagnosis on the identification of strongly SDH-reactive blood vessels, which occurred in 87.5% of the biopsies. The mtDNA mutation was present in 32 of 40 patients (80%). We conclude that there are no clinical and pathologic differences between the patients with and without this mtDNA mutation.

Chronic progressive external ophthalmoplegia: A correlative study of mitochondrial DNA deletions and their phenotypic expression in muscle biopsies

Deleted mitochondrial DNA (mtDNA) has been shown to coexist with normal mtDNA (heteroplasmy) in muscles from chronic progressive external ophthalmoplegia, including Kearns-Sayre syndrome. In this study, we correlated heteroplasmic mtDNA abnormality with clinical, biochemical and histological findings with the following results: (1) large deletions ranging from 1.8 to 8.8 kb in 22 muscle specimens from 28 patients who had ophthalmoplegia clinically and focal cytochrome c oxidase (CCO) deficiency by histochemistry, (2) no difference in clinical and biochemical findings between patients with and without mtDNA deletions, (3) no relationship between the size, site or populations of deleted mtDNA and respiratory chain enzyme activities in muscles, (4) positive correlation between the number of CCO-deficient fibers and the populations of deleted mtDNA, and (5) higher incidence of CCO-negative fibers in patients with deleted mtDNA than in those with no deletion of mtDNA. These results suggest that deleted mtDNA is, at least in part, responsible for focal CCO deficiency as a phenotypic expression and that the investigation on pathogenetic mechanism of focal CCO deficiency may provide a clue to understanding the underlying pathophysiology in this disorder.

A novel D104G mutation in the adenine nucleotide translocator 1 gene in autosomal dominant progressive external ophthalmoplegia patients with mitochondrial DNA with multiple deletions

Autosomal dominant progressive external ophthalmoplegia is a mitochondrial disorder characterized by multiple large deletions of mitochondrial DNA. A recent study showed pathogenic heterozygous missense mutations in the heart/skeletal muscle isoform of the adenine nucleotide translocator 1 gene in autosomal dominant progressive external ophthalmoplegia patients. In one Japanese autosomal dominant progressive external ophthalmoplegia family, we found a novel A‐to‐G heterozygous mutation at nucleotide 311 of the adenine nucleotide translocator 1 gene, which segregated with affected individuals and could not be detected in the genomic DNA sequence of 120 normal controls. This mutation converted a highly conserved aspartic acid into a glycine at codon 104. Polymerase chain reaction analysis of single muscle fibers showed the presence of one type of deletion in each fiber, suggesting clonal expansion of mitochondrial DNA with deletions. These findings support the pathogenesis of the adenine nucleotide translocator 1 gene mutation in human disease.

Mitochondrial DNA mutations in Leigh syndrome and their phylogenetic implications

AbstractOf 100 patients with the clinical diagnosis of Leigh syndrome, 21 were found to have specific enzyme defects: 15 involving cytochrome c oxidase (COX); 4, pyruvate dehydrogenase complex (PDHC); one, complex I (reduced nicotinamide adenine dinucleotide [NADH]-coenzyme Q reductase) and one, complex II (succinate-ubiquinone reductase) deficiencies. In addition to the most common form of COX deficiency, mtDNA mutations in the adenosine triphosphatase (ATPase) 6 coding region were also commonly seen. Eighteen patients (18%) had mtDNA mutations at nucleotide position (np) 8993 or 9176. The mutated DNAs were present in a heteroplasmic state, comprising more than 90% of the DNA in muscle and/or blood samples from all patients. Patients with the T-to-G mutation at np 8993 usually had early onset of the disease with rapid progression, showing the typical clinical features of Leigh syndrome. On the other hand, those with the T-to-C 8993 mutation showed a milder and more chronic course. Patients with the mutation at np 9176 showed variable courses. Phylogenetic analysis of mtDNA D-loop sequences for the patients with the ATPase 6 mutations and normal Japanese subjects revealed that a T-to-G/C mutation at np 8993 and a T-to-C mutation at np 9176 occurred many times independently in the Japanese population.

Apoptosis is suspended in muscle of mitochondrial encephalomyopathies

Abstract. Over the past few years, many studies have been done on the apoptotic involvement in muscle fiber degeneration in various myopathies, but the occurrence of apoptosis in muscles of mitochondrial encephalomyopathies is still controversial. To confirm whether apoptotic processes are truly related to muscle fiber degeneration in mitochondrial encephalomyopathies, we performed the TUNEL method not only at the light microscopic (LM) but also at the electron microscopic (EM) level for muscles of five MELAS, five CPEO and five MERRF patients and five control muscles. Immunohistochemical studies of Bcl-2, Bax, cytochrome c, Apaf-1, activated caspase-3 and human inhibitor of apoptosis protein XIAP, and immunoblotting of Apaf-1 and XIAP were also carried out. In LM-TUNEL, MELAS, CPEO and MERRF patients had only very small numbers of TUNEL-positive myonuclei: 0.13±0.10%, 0.15±0.14% and 0.04±0.09%, respectively. Almost all of them were seen in ragged-red fibers (RRFs). EM-TUNEL showed no significant increase of DNA fragmentation in RRFs despite mild peripheral chromatin condensation. However, Bax and Apaf-1 expression and cytochrome c release from mitochondria were seen in RRFs. Caspase-3 activation was confirmed in 9.0±3.7%, 12.0±4.4% and 12.4±3.8% of RRFs in MELAS, CPEO and MERRF, respectively, but not in control muscles. Almost all RRFs showed sarcoplasmic expression of XIAP. Thus, there is a possibility that, although apoptotic reactions started in muscles of mitochondrial encephalomyopathies, their execution is rarely completed. Sarcoplasmic expression of XIAP probably leads to the suspension of the apoptotic process in mitochondrial encephalomyopathies.

Two pathogenic point mutations exist in the authentic mitochondrial genome, not in the nuclear pseudogene

AbstractTechnical advancements in molecular genetics have shown various mitochondrial DNA (mtDNA) abnormalities in patients with mitochondrial myopathies. Recently, it has been revealed that, in these patients, the nuclear DNA carries sequences similar to those of the mtDNA (nuclear pseudogene) and it has several point mutations previously reported to be pathogenic. We verified the existence of the T3250C and T3291C mutations, which we have found in patients with mitochondrial myopathy, in the authentic mitochondrial genome. A long polymerase chain reaction provides a powerful tool for avoiding nuclear pseudogene amplification and for ruling out ambiguity in the detection of the mutation for diagnosis.

Adult Leigh syndrome with mitochondrial DNA mutation at 8993

Abstract Adult onset Leigh syndrome with a nucleotide (nt) 8993 mutation in mitochondrial (mt) DNA is reported. A 43-year-old woman with a 6-year-history of insulin-resistant diabetes mellitus developed muscular weakness, intractable nausea and vomiting, and anemia. These were followed vertigo, blindness, and deafness with nystagmus. Magnetic resonance imaging (MRI) revealed abnormal high intensities in the bilateral medial regions of the thalamus and periaqueductal gray matters. Autopsy disclosed well-demarcated necrotizing lesions with prominent capillaries in the areas detected by MRI, which were sufficiently diagnostic for Leigh syndrome. MtDNA analysis performed on DNAs extracted from formalin-fixed tissues including liver, heart, brain, muscle, kidney and pancreas showed a T→G mutation at nt 8993. This is the first case of adult Leigh syndrome demonstrating on mtDNA mutations.

Psychosis and progressing dementia: Presenting features of a mitochondriopathy

We report a patient with a C-to-T substitution at nucleotide position 3256 in mitochondrial tRNA-Leu(UUR) gene (C3256T), who showed progressive psychosis and dementia with mild and slowly progressive myopathy. The patient was born in 1952 as the first son of unrelated healthy parents. The medical histories of his mother, sister, and grandmother were unremarkable. He was healthy until age 29, when he showed occasional psychiatric symptoms such as delusion and confusion. He was diagnosed with mitochondrial encephalomyopathy at age 36 based on generalized muscle atrophy and findings of a biopsy sample from the right biceps brachii.1 Over subsequent years, the patient showed periodic psychiatric symptoms, progressive dementia, myoclonus, generalized seizures, ataxia, ophthalmoplegia, and paralytic ileus. However, his myopathy was mild and only slowly progressive; he was able to climb stairs without difficulty at age 45. Lactate and …

A case of MERRF associated with chronic pancreatitis

We report the first case to our knowledge of chronic pancreatitis associated with mitochondrial encephalopathy with the A8344G mitochondrial DNA (mtDNA) mutation. This 10-year-old-girl had suffered from recurrent abdominal pain with elevated serum amylase and lipase since the age of 6, and easy fatigability, tremor and astatic seizures since the age of 8. A biopsy of quadriceps muscle revealed ragged-red-fibers and cytochrome c oxidase deficiency. Analysis of mtDNA in peripheral blood identified an A8344G mutation in the mitochondrial tRNA(Lys) gene. Taken together with physical signs of myoclonic seizures and cerebellar dysfunction, we diagnosed her as myoclonic epilepsy with ragged-red fibers associated with chronic pancreatitis. Although no association between mitochondrial disease and pancreatitis has yet been established, this case suggests it is necessary to consider the participation of mitochondrial abnormality in the pathogenesis of recurrent pancreatitis.

A point mutation of mitochondrial ATPase 6 gene in Leigh syndrome

A T-to-G transition at nucleotide 9176 (T9176G) in the mitochondrial adenosine triphosphate 6 gene (MTATP6) was detected in two siblings with Leigh syndrome. Heteroplasmy was observed in the mothers leukocytes. The T9176G mutation changes a highly conserved leucine residue to an arginine in subunit 6 of ATPase and is maternally inherited like mutations in the other mitochondrial genes. Another mutation in the same codon (T9176C) has been previously reported in Leigh syndrome. This gives strong support to the relevance of MTATP6 dysfunction in Leigh syndrome and the importance of leucine at that position.