A novel mitochondrial tRNA(Phe) mutation inhibiting anticodon stem formation associated with a muscle disease

Acute Respiratory Failure Is the Initial Manifestation in the Adult-Onset A3243G tRNALeu mtDNA Mutation: A Case Report and the Literature Review

Isolated mitochondrial myopathy refers to the condition of mitochondrial disorders that primarily affect the skeletal muscle system. Here we report on a case of a patient who presented with acute respiratory failure as the initial and predominant clinical manifestation after using anesthetic drugs. The diagnosis of mitochondrial myopathy was made by histochemical findings of ragged red fibers with a modified Gomori trichrome Stain in the skeletal muscle biopsy and the genetic detection of an A3243G point mutation in the tRNA^Leu (UUR) gene of mitochondrial DNA (mtDNA) in a peripheral blood specimen. The patient revealed a benign clinical outcome with ventilator assistance and a cocktail treatment. Further, we performed a literature review on patients with respiratory failure as the early and predominant manifestation in adult-onset isolated mitochondrial myopathy. Eleven cases in nine studies (including our case) have been reported, and five of whom underwent DNA analysis all harbored the A3243G mutation in the tRNA^Leu gene of the mtDNA. Use of sedative drugs tends to induce acute respiratory failure in such cases.

Mitochondrial G8292A and C8794T mutations in patients with Niemann-Pick disease type C

Niemann-Pick disease type C (NP-C) is a neurovisceral lipid storage disorder. At the cellular level, the disorder is characterized by accumulation of unesterified cholesterol and glycolipids in the lysosomal/late endosomal system. NP-C is transmitted in an autosomal recessive manner and is caused by mutations in either the NPC1 (95% of families) or NPC2 gene. The estimated disease incidence is 1 in 120,000 live births, but this likely represents an underestimate, as the disease may be under-diagnosed due to its highly heterogeneous presentation. Variants of adenosine triphosphatase (ATPase) subunit 6 and ATPase subunit 8 (ATPase6/8) in mitochondrial DNA (mtDNA) have been reported in different types of genetic diseases including NP-C. In the present study, the blood samples of 22 Iranian patients with NP-C and 150 healthy subjects as a control group were analyzed. The DNA of the blood samples was extracted by the salting out method and analyzed for ATPase6/8 mutations using polymerase chain reaction sequencing. Sequence variations in mitochondrial genome samples were determined via the Mitomap database. Analysis of sequencing data confirmed the existence of 11 different single nucleotide polymorphisms (SNPs) in patients with NP-C1. One of the most prevalent polymorphisms was the A8860G variant, which was observed in both affected and non-affected groups and determined to have no significant association with NP-C incidence. Amongst the 11 polymorphisms, only one was identified in the ATPase8 gene, while 9 including A8860G were observed in the ATPase6 gene. Furthermore, two SNPs, G8292A and C8792A, located in the non-coding region of mtDNA and the ATPase6 gene, respectively, exhibited significantly higher prevalence rates in NP-C1 patients compared with the control group (P<0.01). The present study suggests that there may be an association between mitochondrial ATPase6/8 mutations and the incidence of NP-C disease. In addition, the mitochondrial SNPs identified maybe pathogenic mutations involved in the development and prevalence of NP-C. Furthermore, these results suggest a higher occurrence of mutations in ATPase6 than in ATPase8 in NP-C patients.

Novel mitochondrial tRNA(Ile) m.4282A>G gene mutation leads to chronic progressive external ophthalmoplegia plus phenotype

BACKGROUND/AIM

To investigate the underlying pathomechanism in a 33-year-old female Caucasian patient presenting with chronic progressive external ophthalmoplegia (CPEO) plus symptoms.

METHODS

Histochemical analysis of skeletal muscle and biochemical measurements of individual oxidative phosphorylation (OXPHOS) complexes. Genetic analysis of mitochondrial DNA in various tissues with subsequent investigation of single muscle fibres for correlation of mutational load.

RESULTS

The patient's skeletal muscle showed 20% of cytochrome c oxidase-negative fibres and 8% ragged-red fibres. Genetic analysis of the mitochondrial DNA revealed a novel point mutation in the mitochondrial tRNA(Ile) (MTTI) gene at position m.4282G>A. The heteroplasmy was determined in blood, buccal cells and muscle by restriction fragment length polymorphism (RFLP) combined with a last fluorescent cycle. The total mutational load was 38% in skeletal muscle, but was not detectable in blood or buccal cells of the patient. The phenotype segregated with the mutational load as determined by analysis of single cytochrome c oxidase-negative/positive fibres by laser capture microdissection and subsequent LFC-RFLP.

CONCLUSIONS

We describe a novel MTTI transition mutation at nucleotide position m.4282G>A associated with a CPEO plus phenotype. The novel variant at position m.4282G>A disrupts the middle bond of the D-stem of the tRNA(Ile) and is highly conserved. The conservation and phenotype-genotype segregation strongly suggest pathogenicity and is in good agreement with the MTTI gene being frequently associated with CPEO. This novel variant broadens the spectrum of MTTI mutations causing CPEO.

Mitochondrial myopathy associated with a novel 5522G>A mutation in the mitochondrial tRNA(Trp) gene

We report a novel pathogenic mutation of the mitochondrial transfer RNA (tRNA) gene for tryptophan in a patient with isolated myopathy and persistently elevated creatine kinase. Muscle studies revealed ragged red fibres and decreased activity of respiratory chain complex I and cytochrome c oxidase (COX). Sequencing of the 22 mitochondrial tRNA genes revealed a mutation m.5522G>A, which alters a conserved base pairing in the D-stem of the tRNA for tryptophan. The mutation was heteroplasmic with a mutational load between 88 and 99% in COX-negative fibres. This case contributes to the genetic heterogeneity of mitochondrial diseases caused by mutations in mitochondrial tRNA genes.

A comparative analysis approach to determining the pathogenicity of mitochondrial tRNA mutations

Distinguishing pathogenic from polymorphic changes poses significant problems for geneticists and despite 30 years of postgenomic experience this remains the case in mitochondrial genetics. Base substitutions in mitochondrial tRNA (mt-tRNA) genes are particularly difficult, but important, because they are common causes of pathology and associated with high rates of transmission. Providing accurate genetic advice to patients and their families is of paramount importance in disease prevention, and brings into sharp focus the factors used to distinguish pathogenic from polymorphic variants. We have reevaluated our pathogenicity scoring system for mt-tRNA mutations following a considerable increase in the number reported since the system was devised in 2004. This allowed us to address notable issues including the underestimation of "definitely pathogenic" mutations resulting from insufficient data collection. We illustrate the robustness of our revised scoring system using novel pathogenic and previously reported polymorphic changes and conclude that while clear evidence from single-fiber and/or trans-mitochondrial cybrid studies remains the gold standard for assigning pathogenicity, our scoring system is valuable for deciding which mt-tRNA mutations to investigate further using these labor-intensive techniques.

Successful cochlear implantation in a patient with mitochondrial hearing loss and m.625G>A transition

OBJECTIVE

We present a patient with mitochondrial hearing loss and a novel mitochondrial DNA transition, who underwent successful cochlear implantation.

CASE REPORT

An 11-year-old girl showed epilepsy and progressive hearing loss. Despite the use of hearing aids, she gradually lost her remaining hearing ability. Laboratory data revealed elevated lactate levels, indicating mitochondrial dysfunction. Magnetic resonance imaging showed diffuse, mild brain atrophy. Cochlear implantation was performed, and the patient's hearing ability was markedly improved. Whole mitochondrial DNA genome analysis revealed a novel heteroplasmic mitochondrial 625G>A transition in the transfer RNA gene for phenylalanine. This transition was not detected in blood DNA from the patient's mother and healthy controls. Mitochondrial respiratory chain activities in muscle were predominantly decreased in complex III.

CONCLUSION

This case indicates that cochlear implantation can be a valuable therapeutic option for patients with mitochondrial syndromic hearing loss.

A new phenotype of mitochondrial disease characterized by familial late-onset predominant axial myopathy and encephalopathy

Axial myopathy is a rare neuromuscular disease that is characterized by paraspinal muscle atrophy and abnormal posture, most notably camptocormia (also known as bent spine). The genetic cause of familial axial myopathy is unknown. Described here are the clinical features and cause of late-onset predominant axial myopathy and encephalopathy. A 73-year-old woman presented with a 10-year history of severe paraspinal muscle atrophy and cerebellar ataxia. Her 84-year-old sister also developed late-onset paraspinal muscle atrophy and generalized seizures with encephalopathy. Computed tomography showed severe atrophy and fatty degeneration of their paraspinal muscles. Their mother and maternal aunt also developed bent spines. The existence of many ragged-red fibers and cytochrome c oxidase-negative fibers in the biceps brachii muscle of the proband indicated a mitochondrial abnormality. No significant abnormalities were observed in the respiratory chain enzyme activities; however, the activities of complexes I and IV were relatively low compared with the activities of other complexes. Sequence analysis of the mitochondrial DNA from the muscle revealed a novel heteroplasmic mutation (m.602C>T) in the mitochondrial tRNA^Phe gene. This familial case of late-onset predominant axial myopathy and encephalopathy may represent a new clinical phenotype of a mitochondrial disease.

Impairment of mitochondrial tRNAIle processing by a novel mutation associated with chronic progressive external ophthalmoplegia

We report a sporadic case of chronic progressive external ophthalmoplegia associated with ragged red fibers. The patient presented with enlarged mitochondria with deranged internal architecture and crystalline inclusions. Biochemical studies showed reduced activities of complex I, III and IV in skeletal muscle. Molecular genetic analysis of all mitochondrial tRNAs revealed a G to A transition at nt 4308; the G is a highly conserved nucleotide that participates in a GC base-pair in the T-stem of mammalian mitochondrial tRNA(Ile). The mutation was detected at a high level (approx. 50%) in muscle but not in blood. The mutation co-segregated with the phenotype, as the mutation was absent from blood and muscle in the patient's healthy mother. Functional characterization of the mutation revealed a six-fold reduced rate of tRNA(Ile) precursor 3' end maturation in vitro by tRNAse Z. Furthermore, the mutated tRNA(Ile) displays local structural differences from wild-type. These results suggest that structural perturbations reduce efficiency of tRNA(Ile) precursor 3' end processing and contribute to the molecular pathomechanism of this mutation.

Progressive carotid artery stenosis with a novel tRNA phenylalanine mitochondrial DNA mutation

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) is a distinct clinical syndrome caused by mutations in the mitochondrial DNA. The pathogenesis of stroke-like episodes remains unknown but major vessels stenosis is not a cause of stroke-like episodes. We describe a novel heteroplasmic G617A transition in the mitochondrial transfer RNA phenylalanine gene in a patient with encephalomyopathy who presented with recurrent embolic ischemic strokes accompanied by transient occlusion of middle cerebral, anterior cerebral and internal carotid arteries. These ischemic strokes were presumed to be artery-to artery embolisms associated with carotid artery stenosis. Single muscle fiber analysis revealed the pathogenicity of the mutation although its causative role on carotid artery stenosis remains to be elucidated. This case expands phenotypic spectrum of mitochondrial disorders in terms of macroangiopathy, but macroangiopathy-related ischemic strokes should be distinguished from classic stroke-like episodes of MELAS that are speculated to be microangioapthy-related or non-ischemic neurovascular events.

Identification of novel mutations in five patients with mitochondrial encephalomyopathy

MELAS, MERRF, LHON and NARP, are well-established mitochondrial syndromes associated with specific point mutations of mitochondrial DNA (mtDNA). However, these recurrent mtDNA mutations account for only a minority of mitochondrial disease cases. To evaluate the impact of novel mtDNA mutations, we performed mtDNA sequence analysis in muscle and other tissues of 240 patients with different mitochondrial neuromuscular syndromes. We identified a total of 33 subjects with novel, private or uncommon mutations. Among these, five novel mutations were found in both paediatric and adult cases. We here report on the clinical description of these patients, as well as the biochemical and molecular genetic characterization of the corresponding mutations. Patients 1 and 2 showed changes in ND genes, patient 3 carried a heteroplasmic deletion in the COI gene, patients 4 and 5 carried heteroplasmic mutations in tRNA(Trp) and tRNA(Phe), respectively. Altogether, these data indicate that mtDNA analysis must become part of the routine screening for mitochondrial disorders.

Human mitochondrial transfer RNAs: role of pathogenic mutation in disease

The human mitochondrial genome encodes 13 proteins. All are subunits of the respiratory chain complexes involved in energy metabolism. These proteins are translated by a set of 22 mitochondrial transfer RNAs (tRNAs) that are required for codon reading. Human mitochondrial tRNA genes are hotspots for pathogenic mutations and have attracted interest over the last two decades with the rapid discovery of point mutations associated with a vast array of neuromuscular disorders and diverse clinical phenotypes. In this review, we use a scoring system to determine the pathogenicity of the mutations and summarize the current knowledge of structure-function relationships of these mutant tRNAs. We also provide readers with an overview of a large variety of mechanisms by which mutations may affect the mitochondrial translation machinery and cause disease.

Pathogenic mechanism of a human mitochondrial tRNAPhe mutation associated with myoclonic epilepsy with ragged red fibers syndrome

Human mitochondrial tRNA (hmt-tRNA) mutations are associated with a variety of diseases including mitochondrial myopathies, diabetes, encephalopathies, and deafness. Because the current understanding of the precise molecular mechanisms of these mutations is limited, there is no efficient method to treat their associated mitochondrial diseases. Here, we use a variety of known mutations in hmt-tRNA(Phe) to investigate the mechanisms that lead to malfunctions. We tested the impact of hmt-tRNA(Phe) mutations on aminoacylation, structure, and translation elongation-factor binding. The majority of the mutants were pleiotropic, exhibiting defects in aminoacylation, global structure, and elongation-factor binding. One notable exception was the G34A anticodon mutation of hmt-tRNA(Phe) (mitochondrial DNA mutation G611A), which is associated with MERRF (myoclonic epilepsy with ragged red fibers). In vitro, the G34A mutation decreases aminoacylation activity by 100-fold, but does not affect global folding or recognition by elongation factor. Furthermore, G34A hmt-tRNA(Phe) does not undergo adenosine-to-inosine (A-to-I) editing, ruling out miscoding as a possible mechanism for mitochondrial malfunction. To improve the aminoacylation state of the mutant tRNA, we modified the tRNA binding domain of the nucleus-encoded human mitochondrial phenylalanyl-tRNA synthetase, which aminoacylates hmt-tRNA(Phe) with cognate phenylalanine. This variant enzyme displayed significantly improved aminoacylation efficiency for the G34A mutant, suggesting a general strategy to treat certain classes of mitochondrial diseases by modification of the corresponding nuclear gene.

Mitochondrial myopathy with exercise intolerance and retinal dystrophy in a sporadic patient with a G583A mutation in the mt tRNA(phe) gene

We describe a second patient with the 583G>A mutation in the tRNA(phe) gene of mitochondrial DNA (mtDNA). This 17-year-old girl had a mitochondrial myopathy with exercise intolerance and an asymptomatic retinopathy. Muscle investigations showed occasional ragged red fibers, 30% cytochrome c oxidase (COX)-negative fibers, and reduced activities of complex I+IV in the respiratory chain. The mutation was heteroplasmic (79%) in muscle but undetectable in other tissues. Analysis of single muscle fibers revealed a significantly higher level of mutated mtDNA in COX-negative fibers. Our study indicates that the 583G>A mutation is pathogenic and expands the clinical spectrum of this mutation.

Mutations in mtDNA: are we scraping the bottom of the barrel?

The small, maternally inherited mtDNA has turned out to be a Pandora's box of pathogenic mutations: 12 years into the era of "mitochondrial medicine," about 100 pathogenic point mutations and innumerable rearrangements have been associated with a bewildering variety of multisystemic as well as tissue-specific human diseases. After reviewing the principles of mitochondrial genetics, we compare and contrast the clinical and pathological features of disorders due to mutations in genes affecting mitochondrial protein synthesis with those of mutations in protein-coding genes. In contrast to the striking progress in our understanding of etiology, pathogenesis is only partially explained by the rules of mitochondrial genetics and remains largely terra incognita. We review recent progress in prenatal diagnosis and epidemiology. Therapy is still woefully inadequate, but a number of promising approaches are being developed.

Point mutation tRNA(Ser(UCN)) in a child with hearing loss and myoclonus epilepsy

We report on a family with a 12-year-old boy who suffered from a maternally inherited syndrome characterized by a combination of sensorineural hearing loss, myoclonus epilepsy, ataxia, severe psychomotor retardation, short stature, and diabetes mellitus. First, he showed a muscular hypotonia with hearing loss; later, he developed a myoclonus epilepsy, growth failure, and severe psychomotor retardation. At the age of 10 years, he developed diabetes mellitus. After initiation of combined ubiquinone and vitamin C treatment, we observed a progression in psychomotor development. Lactate and pyruvate levels in blood and cerebrospinal fluid were normal. No ragged red fibers or ultrastructural abnormalities were seen in a skeletal muscle biopsy. Biochemical assays of respiratory chain complex activities revealed decreased activity of complexes I and IV. By sequence analysis of mitochondrial DNA encoding transfer ribonucleic acids (RNAs), a homoplasmic T to C substitution at nucleotide position 7512 was found affecting a highly conserved base pair in the tRNA(ser(UCN)) acceptor stem. Asymptomatic family members of the maternal line were heteroplasmic for the mutation in blood samples. Analysis of mitochondrial DNA in patients with hearing loss and myoclonus epilepsy is recommended, even in the absence of laboratory findings. Therapeutically, ubiquinone and antioxidants can be beneficial.

A novel mutation in the mitochondrial tRNAPhe gene associated with mitochondrial myopathy

We report a novel heteroplasmic T-->C mutation at nt position 582 within the mitochondrial tRNA(Phe) gene of a 70-year-old woman with mitochondrial myopathy. No other family members were affected, suggesting that our patient was a sporadic case. The muscle showed frequent ragged red fibers and 43% cytochrome c oxidase deficient fibers. The mutation alters a conserved base pairing in the aminoacyl acceptor stem. The mutation load was 70% in muscle homogenate and varied from 0 to 95% in individual muscle fiber segments. Cytochrome c oxidase-negative fibers showed significantly higher levels of mutated mtDNA (>75%) than Cytochrome c oxidase-positive fibers (<55%). This mutation adds to the previously described four pathogenic mutations in the tRNA(Phe) gene.

Mitochondrial myopathy and respiratory failure associated with a new mutation in the mitochondrial transfer ribonucleic acid glutamic acid gene

We report a novel T14687C mutation in the mitochondrial transfer ribonucleic acid glutamic acid gene in a 16-year-old boy with myopathy and lactic acidosis, retinopathy, and progressive respiratory failure leading to death. A muscle biopsy showed cytochrome c oxidase-negative ragged-red fibers, and biochemical analysis of the respiratory chain enzymes in muscle homogenate revealed complex I and complex IV deficiencies. The mutation, which affects the trinucleotide (TpsiC) loop, was nearly homoplasmic in the muscle DNA of the proband, but it was absent in his blood and in the blood from the asymptomatic mother, suggesting that it may have been a spontaneous somatic mutation in muscle.

Genotyping of alcohol dehydrogenase type 2 and 3 using a two-buffer polyacrylamide gel electrophoresis system

Genetic polymorphisms in the alcohol dehydrogenase genes, ADH2 and ADH3, have been shown to affect individual susceptibility to diseases such as alcoholism and oesophageal cancer. Although several PCR-based methods for genotyping these enzymes have been previously developed, the two-buffer polyacrylamide gel electrophoresis system has the ability to rapidly resolve all classes of point mutations within 2-3 hours instead of the conventional overnight separation. The success of this technique is partly attributable to a discontinuous two-phase buffer system and horizontal flatbed gel electrophoresis rather than conventional vertical gels. Using a modification of this system, we were able to detect all of the known polymorphisms within ADH2 exons 3 and 9 and ADH3 exon 8, as well as a rare variant within ADH2 exon 9. This method is rapid, cost-effective, and is ideal for large scale screening programmes.

Exercise intolerance, muscle pain and lactic acidaemia associated with a 7497G>A mutation in the tRNASer(UCN) gene

A 13-year-old girl with non-familial exercise intolerance, muscle pain and lactic acidaemia underwent a muscle biopsy for suspected mitochondrial disease. Muscle morphology showed 25% ragged-red fibres and 80% COX-negative staining. Enzymatic activities of mitochondrially co-encoded respiratory chain enzymes (complexes I, III, and IV) were decreased in muscle but normal in cultured skin fibroblasts. mtDNA analysis revealed the presence of the 7497G>A mutation in the tRNASer(UCN) gene, homoplasmic in skeletal muscle and 90% in leukocytes. Analysis of the mother's mtDNA showed 10% heteroplasmy in blood. It may be concluded that the 7497G>A mutation is associated with a muscle-only disease presentation for which high levels of mutated mtDNA are required. Exercise intolerance and muscle pain in otherwise normal children warrants further mitochondrial evaluation.

Mitochondriopathy mimicking amyotrophic lateral sclerosis

BACKGROUND

Mitochondriopathy has been rarely reported to imitate motor neuron disease.

REVIEW SUMMARY

A 57-year-old, 157-cm-tall woman with clinical and electrophysiological features of motor neuron disease since 1993 is reported. She also had increased liver function parameters, hypothyroidism, and sinus tachycardia. Because her mother and sister had both died from assumed amyotrophic lateral sclerosis, familial ALS was diagnosed. On reevaluation, screening for superoxide-dismutase gene mutations was negative, but lactate stress testing was abnormal and muscle biopsy revealed patchy COX deficiency and abnormal mitochondria. Analysis of the muscle mtDNA revealed substitutions in the isoleucine tRNA, in the ATPase-6, and in the cytochrome-b gene, respectively. Based on these data, the diagnosis of ALS was changed to mitochondriopathy.

CONCLUSIONS

Mitochondriopathy may mimic ALS, phenotypically and electrophysiologically. In patients with an ALS phenotype, slow progression, and multisystem involvement, mitochondriopathy should be considered a diagnostic possibility.

Mitochondrial DNA mutations in human disease

The small, maternally inherited mitochondrial DNA (mtDNA) has turned out to be a Pandora's box of pathogenic mutations: 13 years into the era of "molecular mitochondrial medicine," more than 100 pathogenic point mutations and innumerable rearrangements have been associated with a striking variety of multisystemic as well as tissue-specific human diseases. After reviewing the principles of mitochondrial genetics, we consider disorders due to mutations in genes affecting mitochondrial protein synthesis and disorders due to mutations in protein-coding genes. In contrast to the remarkable progress in our understanding of etiology, pathogenesis is only partially explained by the rules of mitochondrial genetics and remains largely unclear. We review recent progress in prenatal diagnosis, epidemiology, and in the development of animal models harboring mtDNA mutations.

Frequency of mitochondrial transfer RNA mutations and deletions in 225 patients presenting with respiratory chain deficiencies

OBJECTIVE

To evaluate the frequency of pathogenic mtDNA transfer RNA mutations and deletions in biochemically demonstrable respiratory chain (RC) deficiencies in paediatric and adult patients.

METHODS

We screened for deletions and sequenced mitochondrial transfer RNA genes in skeletal muscle DNA from 225 index patients with clinical symptoms suggestive of a mitochondrial disorder and with biochemically demonstrable RC deficiency in skeletal muscle.

RESULTS

We found pathogenic mitochondrial DNA mutations in 29% of the patients. The detection rate was significantly higher in adults (48%) than in the paediatric group (18%). Only one pathogenic mutation was detected in the neonatal group. In addition, we describe seven novel transfer RNA sequence variations with unknown pathogenic relevance (six homoplasmic and one heteroplasmic) and 13 homoplasmic polymorphisms. One heteroplasmic transfer RNA(Leu(UUR)) A>G mutation at position 3274 is associated with a distinct neurological syndrome.

CONCLUSIONS

We provide an estimation of the frequency of mitochondrial transfer RNA mutations and deletions in paediatric and adult patients with respiratory chain deficiencies.

Tubulointerstitial nephritis associated with a novel mitochondrial point mutation

BACKGROUND

Nephropathy caused by mitochondrial disorders is a relatively newly recognized disease. Only a few cases have been reported in the literature, and most of them are proximal tubulopathy-presenting Fanconi syndrome. Here we report on a novel mutation in two familial cases of tubulointerstitial nephropathy associated with concentrating defect.

METHODS

Renal biopsy specimens were examined by light microscopy and electron microscopy. Mitochondrial genomic DNA isolated from renal biopsy specimens was amplified by polymerase chain reaction (PCR) and sequenced in its entirety. The DNA sequences were analyzed by (1) comparing with the Anderson et al's mitochondrial sequences; (2) comparing with DNA sequences obtained from 97 human controls, including both healthy individuals and patients with renal diseases; and (3) comparing with the counterparts in 90 different species.

RESULTS

Dismorphic mitochondria with occasional intramitochondrial inclusions were found in the renal tubular epithelial cells. A novel mitochondrial point mutation was identified at the position 608, that is, the distal end of the anticodon stem of the tRNA(Phe) molecule. The A to G substitution at this position was not observed in 97 human controls and was found to be highly conserved in evolution.

CONCLUSIONS

We have identified an A608G mutation of mitochondrial genome in two cases whose presentation include tubulointerstitial nephritis and stroke.