Mitochondrial DNA Point Mutations Research Articles

Executive and visuospatial deficits in patients with chronic progressive external ophthalmoplegia and Kearns-Sayre syndrome.

Although neuropsychological deficits have been reported in mitochondrial cytopathies, patients with chronic progressive external ophthalmoplegia (CPEO) or Kearns-Sayre syndrome (KSS) have not been studied systematically using a comprehensive test battery. The aim of our study was to assess the range and extent of putative cognitive dysfunction in 22 patients with CPEO or KSS, and to compare cognitive performance of patients with healthy control subjects matched for age, sex and years of education. Genetic analysis of skeletal muscle tissue from 22 patients with CPEO or KSS included screening for mitochondrial DNA (mtDNA) point mutations (3243/8344) and mtDNA deletions. All patients were examined by a neuropsychological test battery covering verbal skills, verbal and visual memory, visuo-spatial perception, visual construction, attention, abstraction and flexibility, and Quality of Life. Molecular genetic analysis of mtDNA revealed single large-scale deletions in 15 out of 22 patients and the tRNA (Leu) A3243G point mutation in two out of 22 patients. In five out of 22 patients none of the frequently encountered mtDNA mutations could be detected. Neuropsychological testing did not reveal general intellectual deterioration, but specific cognitive deficits, particularly in visual construction, attention and abstraction/flexibility. Subgroup analysis of 15 patients with mtDNA deletions showed similar results when compared with the full group. In our series of patients with CPEO or KSS neuropsychological testing did not reveal signs that would suggest general intellectual decline or dementia, but provided evidence of specific focal neuropsychological deficits, suggesting particular impairment of visuospatial perception associated to parieto-occipital lobes and executive deficits associated to the prefrontal cortex.

Accumulation of point mutations in mitochondrial DNA of aging mice

Mitochondrial DNA (mtDNA) exists in a highly genotoxic environment created by exposure to reactive oxygen species, somewhat deficient DNA repair, and the relatively low fidelity of polymerase gamma. Given the severity of the environment, it was anticipated that mutation accumulation in the mtDNA of aging animals should exceed that of nuclear genes by several orders of magnitude. We have analyzed fragments amplified from the D-loop region of mtDNA from 2 to 22-month-old mice. The amplified 432 bp fragments were cloned into plasmid vectors, and plasmid DNAs from individual clones were purified and sequenced. None of 110 fragments from young mice contained a mutation, while 9 of 87 clones originating from old animals contained base substitutions (chi square = 11.9, P<0.001). The estimated mutation frequency in mtDNA from old mice was 11.6±2.7 or 25.4±7.8 per 10 5 nucleotides (depending on assumptions of clonality), which exceeds existing estimates for mutation frequencies for nuclear genes by approximately 1000-fold. Our data suggest that at 22 months of age, which roughly corresponds to 3/4 of the mouse natural life span, most mtDNA molecules carry multiple point mutations.

Marin-Garcia et al: Striated Muscle Mitochondrial Phenotype: Probing striated muscle mitochondrial phenotype in neuromuscular disorders

Multisystemic disorders with predominantly neurologic manifestations often present with mitochondrial abnormalities in striated muscle biopsies. Decreased respiratory complex activities and abnormalities in mitochondrial structure and DNA constitute the spectrum of mitochondrial changes used as diagnostic and prognostic indicators in patients with neuromuscular disorders. This study assessed mitochondrial defects present in a cohort of 154 young patients to determine diagnostic efficiency and probe the relationship of mitochondrial to clinical phenotype. Striated muscle biopsies were analyzed for mitochondrial structure and number, levels of enzyme activities of complex I-V and citrate synthase, mitochondrial DNA and specific mitochondrial DNA deletions, and presence of 15 pathogenic mitochondrial DNA point mutations. Reduced complex I, III, IV, and V activities were the most ubiquitous finding, with complex III most commonly affected. Mitochondrial structural defects (39%) included changes in mitochondria sizes/shapes and number and aberrant cristae formation. Mitochondrial DNA deletions were evident in 15 patients, three displayed mitochondrial DNA depletion, and only two harbored pathogenic point mutations. Reductions in specific enzyme activities may be the most sensitive diagnostic indicator, whereas defects in ultrastructure and mitochondrial DNA integrity were frequently accompanied by the full spectrum of mitochondrial abnormalities. Some phenotypes displayed specific mitochondrial abnormalities; however, most clinical phenotypes displayed little specificity with regard to mitochondrial phenotype.

A novel mtDNA C11777A mutation in Leigh syndrome

A novel mitochondrial DNA point mutation, a C-to-A mutation at nucleotide position (np) 11,777, was identified in two unrelated patients out of 100 with Leigh syndrome. This mutation converted a highly evolutionary conserved arginine to a serine at codon 340 in ND4 gene. This codon was also converted by a G-to-A mutation at np 11,778, the most common mutation associated with Leber's hereditary optic neuropathy (LHON), but the amino acid replacement was different (R340S vs. R340H). Cybrid study revealed that the percentage of heteroplasmy was correlated with complex I function and that the novel mutation caused a much more deleterious effect than the np 11,778 LHON mutation in complex I activity.

The oxidative damage theory of aging

The oxidative stress theory of aging postulates that age-associated reductions in physiologic functions are caused by a slow steady accumulation of oxidative damage to macromolecules, which increases with age and which is associated with life expectancy of organisms. A corollary is that the rate of aging should be retarded by attenuation of oxidative damage. A large body of evidence has accumulated in support of this hypothesis. Increases in oxidative damage to DNA, proteins, and lipids have all been found with normal aging. Genetic manipulation of oxidative damage can increase life expectancy in animals. Overexpression of Cu/Zn superoxide dismutase or manganese superoxide dismutase appears to extend life span. Overexpression of methionine sulfoxide reductase in Drosophila resulted in a 70% increase in survival, and a 50% reduction in methionine sulfoxide reductase in mice resulted in a 30% reduction in life span. Caloric restriction, which extends life span, also reduces oxidative stress. Manipulation of gene expression in Drosophila with phenylbutyrate significantly increases lifespan, and is associated with a 50-fold increase in expression of manganese superoxide dismutase. We recently further examined the mitochondrial DNA theory of aging, which proposes that mitochondrial DNA accumulates mutations with age and that these contribute to the physiological decline in aging. Using a PCR-cloning-sequencing strategy, we found a significant increase in aggregate burden of mitochondrial DNA point mutations in brain in elderly subjects compared to younger subjects. The average aggregate mutational burden in elderly subjects was 2×10 −4 mutations per base. The bulk of these mutations were individually rare point mutations, and 60% changed an amino acid. Cytochrome oxidase activity correlated negatively with increased mutational burden. These findings bolster the possibility that oxidative damage to mitochondrial DNA may play a significant role in normal aging.

Expression pattern of mitochondrial respiratory chain enzymes in skeletal muscle of patients harboring the A3243G point mutation or large-scale deletions of mitochondrial DNA.

To assess the detailed expression pattern of mitochondrial-encoded proteins in skeletal muscle of patients with mitochondrial diseases we performed determinations of cytochrome content and enzyme activities of respiratory chain complexes of 12 patients harboring large-scale deletions and of 10 patients harboring the A3243G mutation. For large-scale deletions we observed a mutation gene dose-dependent linear decline of cytochrome aa3 content, cytochrome c oxidase (COX) activity, and complex I activity. The content of cytochromes b and the complex III activity was either not affected or only weakly affected by the deletion mutation and did not correlate to the degree of heteroplasmy. In contrast, in skeletal muscle harboring the A3243G mutation all investigated enzymes containing mitochondrial-encoded subunits were equally affected by the mutation, but we observed milder enzyme deficiencies at a comparable mutation gene dose. The results of single fiber analysis of selected biopsies supported these findings but revealed differences in the distribution of COX deficiency. Whereas predominantly type I fibers were affected in A3243G and deletion CPEO biopsies, we observed in MELAS and KSS biopsies higher quantities of COX-deficient type 2 fibers. Our findings indicate different pathomechanisms of deletion and A3243G mutations.

A practical approach to the diagnosis and management of MELAS: case report and review.

Mitochondrial encephalomyopathy, lactic acidosis with stroke-like episodes (MELAS) is a mitochondrial disorder and an important diagnostic consideration in the young patient with nonhemorrhagic stroke. Its presentation is varied and diagnosis is based on early recognition of the clinical features and correct interpretation of laboratory and radiologic studies. In this article, we report a patient with MELAS and review the clinical, laboratory, and neuroradiologic features of the condition. In the young patient with multiple stroke-like episodes in different vascular territories and neuroradiologic features of transient abnormalities in varying regions, laboratory testing for MELAS must be performed. The presence of ragged red fibers in skeletal muscle and biochemical demonstration of defects in mitochondrial respiratory enzymes strongly support the diagnosis. Molecular genetic testing for abnormalities in mitochondrial DNA will confirm the diagnosis. The importance of a thorough assessment of family history is also emphasized. The basic principles of mitochondrial genetics and the common point mutations and rearrangements of mitochondrial DNA associated with MELAS are reviewed. Although treatment options are limited, several therapeutic agents have been studied. The diagnosis of MELAS should be considered in the young patient with stroke, especially when accompanied by other clinical features such as seizures, encephalopathy, and muscle weakness. Laboratory evaluation can provide an accurate diagnosis, especially when the appropriate mitochondrial DNA studies are performed. Genetic counseling should be provided to patients with MELAS associated with mitochondrial DNA point mutations. Better understanding of the molecular basis of the condition may result in the development of effective treatment strategies.

Induction of a large deletion in mitochondrial genome of mouse cells by X-ray irradiation

Large deletions and point mutations of mitochondrial DNA (mtDNA) is causally associated with mitochondrial diseases, and accumulates with age in human tissues. In order to find out the role of oxidative stress in the generation of large mtDNA deletions, using normal Balb and severe combined immunodeficiency (SCID) mouse cells, we assessed whether X-ray irradiation induces large mtDNA deletions. Cultured cells were irradiated with X-rays and assayed for a large mtDNA deletion using a PCR technique with a specific pair of primers. X-ray doses as low as 1 Gy were effective for the induction of the large mtDNA deletion (5823 bp long), which corresponds to the human 4977 bp common deletion. The breakpoints were flanked by the 5-bp long tandem repeats, 5′-TACCC-3′. A dose-dependent induction of the large mtDNA deletion was observed, the yield being higher in normal cells than in SCID cells. The fraction of large mtDNA deletion increased in the normal cells but decreased in the SCID cells within 7 days after X-ray irradiation. As the SCID cells carry a mutation in the gene encoding DNA–PKcs, the key enzyme in DNA double-strand break repair, it can be concluded that repair of DNA strand breaks may be involved in the formation of X-ray induced large mtDNA deletions.

Go Forth and Multiply: Mutations in mitochondrial DNA take over (Mitochondria)

A few rabble-rousers can undermine a whole country if they patiently bring others to their side. Similarly, minority mitochondrial DNAs can apparently swamp other kinds to dominate a cell, according to new work. Although preliminary, the results bolster the theory that changes to the mitochondrial genome underlie aging. Mitochondria produce energy for cells, but in the process they churn out toxic molecules called reactive oxygen species (ROS) (see "The Two Faces of Oxygen" ). Mitochondria carry their own genome, and, because of its proximity to the source of ROS, mitochondrial DNA is especially vulnerable to attack. Accumulation of mutations from such assaults could underlie aging, scientists have speculated. The theory has a flaw, however: Because each cell contains multiple mitochondria, a normal gene in one mitochondrion could compensate for a mutated gene in another, effectively canceling out the mutation. As a result, buildup of random mutations shouldn't cripple a cell. In contrast, buildup of the same mutation in different mitochondria could cause trouble, and previous work suggests that such events can occur. The same point mutation--a change to a single DNA base--can amass in different mitochondria of cultured human cells. Nekhaeva and colleagues wondered whether one type of mitochondrial genome could overwhelm other versions in individual cells. They isolated mitochondrial DNA from single cells obtained from 13 human subjects who ranged in age from a few months to more than 100 years, and then they used the polymerase chain reaction to amplify the DNA. The researchers sequenced a portion of the genome and looked for changes in its sequence by comparing it to the average sequence of many cells from the same individual. In single cells from older people, the majority of mitochondrial genomes carried a mutation at the same position, suggesting that one mitochondrion can proliferate until it dominates. Cells from younger people rarely contained such propagated mutations, hinting that the alterations crop up with age rather than being present throughout life. How this "clonal expansion" of mitochondrial mutations occurs isn't clear, but study author Konstantin Khrapko of Harvard Medical School in Boston offers two possibilities. The random redistribution of mitochondria during cell division could, over many divisions, result in cells dominated by a single version of a mitochondrial genome. Alternatively, a mutation that offers an advantage, such as increasing the number of times the organelle duplicates, could help a mitochondrial genome rise to the top. "But this is just speculation," says Krhapko. "The main point is that these clonal expansions exist." The study rebuts a criticism of the mitochondrial theory of aging, says biochemist Simon Melov of the Buck Institute for Age Research in Novato, California. "There was a consensus that mitochondrial DNA point mutations weren't relevant to aging" because they didn't accumulate in large numbers, he says. The work doesn't address whether the mutations alter mitochondrial and cellular functions, but "the levels [of mutations] reported here are consistent with those found in human diseases." Melov cautions that the study examined a few individuals and a limited region of the mitochondrial genome. Nevertheless, it hints that point mutations are more subversive than previously thought. --R. John Davenport E. Nekhaeva, N. D. Bodyak, Y. Kraytsberg, S. B. McGrath, N. J. Van Orsouw, A. Pluzhnikov, J. Y. Wei, J. Vijg, K. Khrapko, Clonally expanded mtDNA point mutations are abundant in individual cells of human tissues. Proc. Natl. Acad. Sci. U.S.A. , 9 April 2002 [e-pub ahead of print]. [Abstract] [Full Text]

Sideroblastic anaemias.

Sideroblastic anaemias.

Ageing muscle: clonal expansions of mitochondrial DNA point mutations and deletions cause focal impairment of mitochondrial function

Although mitochondrial DNA deletions have been shown to accumulate in cytochrome c oxidase deficient muscle fibres of ageing muscle, this has not been demonstrated for point mutations. In this study, we investigated the occurrence of mitochondrial DNA alterations (point mutations and deletions) in cytochrome c oxidase deficient muscle fibres from 14 individuals, without muscle disease, aged 69–82 years. Immunohistochemical investigation showed that the majority of the cytochrome c oxidase deficient muscle fibres expressed reduced levels of subunit II of cytochrome c oxidase, which is encoded by mitochondrial DNA, whereas there was normal or increased expression of subunit IV of cytochrome c oxidase, which is encoded by nuclear DNA. This pattern is typical for mitochondrial DNA mutations causing impaired mitochondrial translation. Single muscle fibres (109 cytochrome c oxidase deficient and 109 normal fibres) were dissected and their DNA extracted. Mitochondrial DNA point mutations were searched for in five tRNA genes by denaturing gradient gel electrophoresis while deletions were looked for by polymerase chain reaction amplification. High levels of clonally expanded point mutations were identified in eight cytochrome c oxidase deficient fibres but in none of the normal ones. They included the previously described pathogenic tRNA Leu(UUR)A3243G and tRNA LysA8344G mutations and three original mutations: tRNA MetT4460C, tRNA MetG4421A, and a 3-bp deletion in the tRNA Leu(UUR) gene. Four different large-scale mitochondrial DNA deletions were identified in seven cytochrome c oxidase deficient fibres and in one of the normal ones. There was no evidence of depletion of mitochondrial DNA by in situ hybridisation experiments. Our data show that mitochondrial DNA point mutations, as well as large-scale deletions, are associated with cytochrome c oxidase deficient muscle fibre segments in ageing. Their focal accumulation causes significant impairment of mitochondrial function in individual cells in spite of low overall levels of mitochondrial DNA mutations in muscle.

Identifying allogeneic platelets by resolution of point mutations in mitochondrial DNA using single-stranded conformational polymorphism PCR.

The purpose of this study was to evaluate single-stranded conformational polymorphism (SSCP)-PCR utilizing two different regions of mitochondrial DNA (mtDNA) as a method to discriminate between donor platelets and recipient cells. Twenty-eight mixtures of platelets (1:1 ratio) were prepared from eight randomly selected persons to simulate donor-recipient combinations after allogeneic platelet transfusion. The mtDNA was extracted from each donor and each prepared mixture. Four primer pairs were designed to amplify two regions of mtDNA, hypervariable region (HVR) 1 and 2. An SSCP-PCR method was developed to analyze the four different amplicons. In addition, the amplified DNA samples containing HVR1 and HVR2 mtDNA of the eight persons were sequenced by using dye-terminator cycle sequencing to determine mtDNA polymorphisms. With four different primer pairs and SSCP-PCR, it was possible to discriminate between donor and recipient DNA in all 28 combinations. DNA sequencing confirmed that the suspected differences were localized within the amplicons examined by SSCP-PCR. SSCP-PCR analysis targeting the HVR1 and HVR2 mtDNA is a promising new method to potentially identify donor cells on the basis of mtDNA polymorphisms. The method does not require prior knowledge of sequence differences between donor and recipient and can be optimized to quantify the amount of residual transfused allogeneic platelets.

Molecular analysis of diabetes mellitus-associated A3243G mitochondrial DNA mutation in Taiwanese cases

Investigation of the clinical manifestations of MELAS-specific A3243G mitochondrial DNA (mtDNA) point mutation has suggested that the A3243G mutation of mtDNA can cause certain subtypes of diabetes mellitus (DM) and contributes about 0.15% of the overall incidence of diabetes. However, a relationship between the diabetic syndrome and the proportion of mutant mtDNA in affected tissues remains unclear. In this article, we report the results of our investigation of 14 diabetic and 23 non-diabetic patients who had the A3243G mutant mtDNA. The proportions of mutant mtDNA in different tissues were noted to change variably and neither heteroplasmy of mutant mtDNA in various tissues nor the proportion of mutated mtDNA in a specific tissue showed a correlation with the clinical phenotype of DM. Generation of a diabetic syndrome was not predictable from either the content of mutant mtDNA in leukocytes, hair follicles, or in muscle tissues. Further study showed that muscle tissue has the highest proportion of mutant mtDNA followed by hair follicles and by blood cells. Moreover, we observed that as the patient's age increased, all tissue showed a declining proportion of mutant mtDNA. These findings suggest that age may play a role in the manifestation of diabetes in patients with A3243G mutation of mtDNA.

Mitochondrial DNA point mutation in the COI gene in a patient with McArdle's disease

We studied a 57-year-old female patient with clinical and biochemical evidences of McArdle's disease. Her muscle biopsy also revealed signs of mitochondrial proliferation, scattered RRF, and a deficit in complex I of the respiratory chain. Molecular genetic analysis showed that the patient was heterozygous for the most common mutation at codon 49 in the myophosphorylase gene. Mitochondrial DNA analysis of muscle tissue revealed an additional G-to-A transition at nucleotide position 7444 in the cytochrome c oxidase subunit I (COI) gene.

A suspected case of proximal diabetic neuropathy predominantly presenting with scapulohumeral muscle weakness and deep aching pain

A 48-year-old man with a 14-year history of type 2 diabetes with proliferative diabetic retinopathy and distal symmetrical diabetic polyneuropathy visited our hospital. Eight months later, he subacutely developed difficulty in both shoulder movement and trouble standing up from a squatting position. This was accompanied by severe bilateral shoulder and thigh pain. Magnetic resonance imaging of the brain, cervical and lumbar spine, computed tomography of the shoulder and X-ray films of the cervical spine and shoulder revealed no abnormality. Cerebrospinal fluid showed a mild elevation of protein (0.93 g/l) without cell infiltration. Antiganglioside antibodies and point mutation of mitochondrial DNA at position 3243 were not found. Neuropathology of the sural nerve showed a moderate myelinated fiber loss, active axonal degeneration, but onion-bulb formation, endoneurial or epineurial vasculitis were not observed. Electromyography revealed neurogenic changes in the proximal upper limb muscles. Nerve conduction studies revealed mild bilateral slowing in nerve conduction velocity in both of the upper and lower limbs. The diagnosis of this patients was suspected to be a proximal diabetic neuropathy (diabetic amyotrophy). The pain and muscle weakness had persisted more severely in the shoulder than in the thigh throughout the clinical course. His unbearable symptoms could be partially alleviated by an administration of a selective serotonin reuptake inhibitor, fluvoxamine maleate. Proximal diabetic neuropathy is a rare disabling type of neuropathy, which is characterized with subacute bilateral muscle weakness and wasting in the proximal part of the lower limbs. The involvement of the scapulohumeral region observed in this case is very unusual in proximal diabetic neuropathy.

The determination of complete human mitochondrial DNA sequences in single cells: implications for the study of somatic mitochondrial DNA point mutations.

Studies of single cells have previously shown intracellular clonal expansion of mitochondrial DNA (mtDNA) mutations to levels that can cause a focal cytochrome c oxidase (COX) defect. Whilst techniques are available to study mtDNA rearrangements at the level of the single cell, recent interest has focused on the possible role of somatic mtDNA point mutations in ageing, neurodegenerative disease and cancer. We have therefore developed a method that permits the reliable determination of the entire mtDNA sequence from single cells without amplifying contaminating, nuclear-embedded pseudogenes. Sequencing and PCR-RFLP analyses of individual COX-negative muscle fibres from a patient with a previously described heteroplasmic COX II (T7587C) mutation indicate that mutant loads as low as 30% can be reliably detected by sequencing. This technique will be particularly useful in identifying the mtDNA mutational spectra in age-related COX-negative cells and will increase our understanding of the pathogenetic mechanisms by which they occur.

Epileptic phenotypes associated with mitochondrial disorders.

To define the clinical and EEG features of the epileptic syndromes occurring in adult and infantile mitochondrial encephalopathies (ME). Thirty-one patients with recurrent and apparently unprovoked seizures associated with primary ME were included in the study. Diagnosis of ME was based on the recognition of a morphologic, biochemical, or molecular defect. Epileptic seizures were the first recognized symptom in 53% of the patients. Many adults (43%) and most infants (70%) had nontypical ME phenotypes. Partial seizures, mainly with elementary motor symptoms, and focal or multifocal EEG epileptiform activities characterized the epileptic presentation in 71% of the patients. Generalized myoclonic seizures were an early and consistent symptom only in the five patients with an A8344G mitochondrial DNA point mutation with classic myoclonus epilepsy with ragged red fibers (MERRF) syndrome or "overlapping" characteristics. Photoparoxysmal EEG responses were observed not only in patients with typical MERRF, but also in adult patients with ME with lactic acidosis and strokelike episodes (MELAS), or overlapping phenotypes, and in one child with Leigh syndrome. Epilepsy is an important sign in the early presentation of ME and may be the most apparent neurologic sign of nontypical ME, often leading to the diagnostic workup. Except for those with an A8344G mitochondrial DNA point mutation, most of our patients had partial seizures or EEG signs indicating a focal origin.

Human mitochondrial DNA diseases

The mitochondrial encephalomyopathies are a genetically heterogeneous group of disorders associated with impaired oxidative phosphorylation. Patients may exhibit a wide range of clinical symptoms and experience significant morbidity and mortality. There is currently no curative treatment. At present the majority of genetically defined mitochondrial encephalomyopathies are caused by mutations in mitochondrial DNA. The underlying molecular mechanisms and the complex relationship between genotype and phenotype in these mitochondrial DNA diseases remain only partially understood. We describe the key features of mitochondrial DNA genetics and outline some of the common disease phenotypes associated with mtDNA defects. A classification of pathogenic mitochondrial DNA point mutations which may have therapeutic implications is outlined.

The incidence of mitochondrial encephalomyopathies in childhood: Clinical features and morphological, biochemical, and DNA abnormalities

In this study we present incidence, point prevalence, and mortality figures of mitochondrial encephalomyopathies in a population-based study of children from western Sweden. Through the screening of registers and review of medical records, we identified 32 patients under 16 years of age from the study population who were diagnosed between January 1, 1984, and December 31, 1998. The incidence of mitochondrial encephalomyopathies in preschool children (<6 years of age) was 1 out of 11,000. The preschool incidence of Leigh's syndrome was 1 out of 32,000, and the preschool incidences of both Alper's syndrome and infantile mitochondrial myopathy with cytochrome C oxidase deficiency were 1 out of 51,000. The point prevalence January 1, 1999) of mitochondrial encephalomyopathies in children under 16 years of age was 1 out of 21,000. The median survival for patients with infantile onset was until 12 years of age. We identified 4 cases with mitochondrial DNA point mutations, 2 cases with mitochondrial DNA deletions, and 2 cases with nuclear mutations in the SURF1 gene. We conclude that mitochondrial encephalomyopathies are relatively common neurometabolic disorders in childhood.

Two point mutations in mitochondrial DNA of cytochrome c oxidase coexist with normal mtDNA in a patient with Alzheimer’s disease

The mitochondrial cytochrome c oxidase (CO) gene sequence was determined on a patient with Alzheimer’s disease (AD). Compared to the standard Cambridge sequence to identify base changes,two missense mutations were found in the patient with AD. The mutations were a G to T transition at np 8206 and an A to T transition at np 8224. The np 8206 mutation changed a Met to an Ile and np 8224 mutation changed a Leu to a Phe. The normal bases and the mutations of mitochondrial DNA (mtDNA) coexist in the patient. Further studies will be required to demonstrate the role of the point mutations of mitochondrial DNA in the pathogenisis of Alzheimer’s disease.