Large-scale Mitochondrial DNA Deletions Research Articles

Disease progression in patients with single, large-scale mitochondrial DNA deletions

Single, large-scale deletions of mitochondrial DNA are a common cause of mitochondrial disease and cause a broad phenotypic spectrum ranging from mild myopathy to devastating multi-system syndromes such as Kearns-Sayre syndrome. Studies to date have been inconsistent on the value of putative predictors of clinical phenotype and disease progression such as mutation load and the size or location of the deletion. Using a cohort of 87 patients with single, large-scale mitochondrial DNA deletions we demonstrate that a variety of outcome measures such as COX-deficient fibre density, age-at-onset of symptoms and progression of disease burden, as measured by the Newcastle Mitochondrial Disease Adult Scale, are significantly (P < 0.05) correlated with the size of the deletion, the deletion heteroplasmy level in skeletal muscle, and the location of the deletion within the genome. We validate these findings with re-analysis of 256 cases from published data and clarify the previously conflicting information of the value of these predictors, identifying that multiple regression analysis is necessary to understand the effect of these interrelated predictors. Furthermore, we have used mixed modelling techniques to model the progression of disease according to these predictors, allowing a better understanding of the progression over time of this strikingly variable disease. In this way we have developed a new paradigm in clinical mitochondrial disease assessment and management that sidesteps the perennial difficulty of ascribing a discrete clinical phenotype to a broad multi-dimensional and progressive spectrum of disease, establishing a framework to allow better understanding of disease progression.

Extraocular Muscle Atrophy and Central Nervous System Involvement in Chronic Progressive External Ophthalmoplegia

BackgroundChronic progressive external ophthalmoplegia (CPEO) is a classical mitochondrial ocular disorder characterised by bilateral progressive ptosis and ophthalmoplegia. These ocular features can develop either in isolation or in association with other prominent neurological deficits (CPEO+). Molecularly, CPEO can be classified into two distinct genetic subgroups depending on whether patients harbour single, large-scale mitochondrial DNA (mtDNA) deletions or multiple mtDNA deletions secondary to a nuclear mutation disrupting mtDNA replication or repair. The aim of this magnetic resonance imaging (MRI) study was to investigate whether the ophthalmoplegia in CPEO is primarily myopathic in origin or whether there is evidence of contributory supranuclear pathway dysfunction.MethodsTen age-matched normal controls and twenty patients with CPEO were recruited nine patients with single, large-scale mtDNA deletions and eleven patients with multiple mtDNA deletions secondary to mutations in POLG, PEO1, OPA1, and RRM2B. All subjects underwent a standardised brain and orbital MRI protocol, together with proton magnetic resonance spectroscopy in two voxels located within the parietal white matter and the brainstem.ResultsThere was evidence of significant extraocular muscle atrophy in patients with single or multiple mtDNA deletions compared with controls. There was no significant difference in metabolite concentrations between the patient and control groups in both the parietal white matter and brainstem voxels. Volumetric brain measurements revealed marked cortical and cerebellar atrophy among patients with CPEO+ phenotypes.ConclusionThe results of this study support a primary myopathic aetiology for the progressive limitation of eye movements that develops in CPEO.

Retraction Note to: Kearns Sayre Syndrome - Case Report with Review of Literature

Kearns-Sayre Syndrome is form of rare mitochondrial cytopathy, first described by Thomas P. Kearns and George Pomeroy Sayre in 1958 and is characterized by progressive external opthalmoplegia, cardiac conduction block, pigmentary retinal degeneration, variable number of red ragged fibers on muscle biopsy. It presents before the child reaches the age of twenty. Kearns-Sayre syndrome may affect many organ systems and additional features may include myopathy, dystonia, bulbar symptoms in the form of dysarthria and nasal regurgitation and bilateral facial weakness. Endocrine abnormalities (e.g., diabetes, growth retardation/short stature, and hypoparathyroidism), bilateral sensorineural deafness, dementia, cataracts, and proximal renal tubular acidosis, skeletal muscle weakness (proximal more than distal) and exercise intolerance are additional features. Kearns Sayre Syndrome occurs as a result of large-scale single deletions (or rearrangements) of mitochondrial DNA (mtDNA), which is usually not inherited but occurs spontaneously, probably at the germ-cell level or very early in embryonic development. No disease-modifying therapy is available for Kearns-Sayre syndrome (KSS). Management is supportive vigilance for detection of associated problems. In the future, potential treatment in patients with Kearns-Sayre syndrome may attempt to inhibit mutant mtDNA replication or encourage replication of wild-type mtDNA.

Chronic progressive external ophthalmoplegia coexistent with motor neuron disease in a patient with a novel large-scale mitochondrial DNA deletion

Chronic progressive external ophthalmoplegia coexistent with motor neuron disease in a patient with a novel large-scale mitochondrial DNA deletion

Natural History of Conduction Abnormalities in a Patient with Kearns-Sayre Syndrome

Kearns-Sayre syndrome is a rare mitochondrial disorder characterized by large-scale deletion or rearrangement of mitochondrial DNA, which is usually not inherited but occur spontaneously probably at the germ cell level or very early in embryonic development by Mehndiratta et al. (Neurol India 50:162-167, 2002). Neuromuscular and cardiac conduction abnormalities are most commonly involved in these patients, which may have subtle presenting signs.

Progressive External Ophthalmoplegia in Southwestern Finland: A Clinical and Genetic Study

Background: Progressive external ophthalmoplegia (PEO) is a common phenotype of mitochondrial disease. Molecu- lar etiologies include sporadic, large-scale deletions in mitochondrial DNA (mtDNA), multiple mtDNA deletions secondary to autosomal dominant or recessive mutations and mtDNA point mutations. Methods: We studied the prevalence and clinical and genetic characteristics of PEO in a defined population in southwestern Finland. A total of 620 patients were first identified from the patient registry at the Turku University Hospital over an 18-year period. The medical records of these patients were scrutinized, and those with clinical features compatible with PEO were ascertained. Results: We identified 10 patients with possible PEO. The patients were examined clinically, and DNA was analyzed for mtDNA deletions and for the m.3243A>G and m.8344A>G mtDNA point mutations. The ANT1, PEO1, POLG1 and POLG2 genes were sequenced. We confirmed the clinical diagnosis of PEO in 6 patients. Large-scale mtDNA deletions were detected in 3 out of 6 PEO patients and mutations in the POLG1 gene in 1 out of 6. We did not find any mutations in the ANT1, PEO1 or POLG2 genes. Conclusions: Our results suggest that molecular investigation of patients with PEO, either sporadic or familial, should start with an analysis for mtDNA deletions, followed by an analysis of the POLG1 gene.

RETRACTED ARTICLE: Kearns Sayre Syndrome—Case Report with Review of Literature

Kearns-Sayre Syndrome is form of rare mitochondrial cytopathy, first described by Thomas P. Kearns and George Pomeroy Sayre in 1958 and is characterized by progressive external opthalmoplegia, cardiac conduction block, pigmentary retinal degeneration, variable number of red ragged fibers on muscle biopsy. It presents before the child reaches the age of twenty. Kearns-Sayre syndrome may affect many organ systems and additional features may include myopathy, dystonia, bulbar symptoms in the form of dysarthria and nasal regurgitation and bilateral facial weakness. Endocrine abnormalities (e.g., diabetes, growth retardation/short stature, and hypoparathyroidism), bilateral sensorineural deafness, dementia, cataracts, and proximal renal tubular acidosis, skeletal muscle weakness (proximal more than distal) and exercise intolerance are additional features. Kearns Sayre Syndrome occurs as a result of large-scale single deletions (or rearrangements) of mitochondrial DNA (mtDNA), which is usually not inherited but occurs spontaneously, probably at the germ-cell level or very early in embryonic development. No disease-modifying therapy is available for Kearns-Sayre syndrome (KSS). Management is supportive vigilance for detection of associated problems. In the future, potential treatment in patients with Kearns-Sayre syndrome may attempt to inhibit mutant mtDNA replication or encourage replication of wild-type mtDNA.

The generation of mitochondrial DNA large-scale deletions in human cells

Large-scale deletions of human mitochondrial DNA (mtDNA) are a common cause of mitochondrial diseases. In order to prevent and treat these mitochondrial diseases, it is important and necessary to understand the mechanisms behind the generation of these deletions. Generally, there exist three kinds of large-scale deletions: deletions almost occur within two direct repeats with identical sequences (class I deletions), deletions are flanked by imperfect repeats (class II deletions) and by no direct repeats (class III deletions). Two major hypotheses are suggested to generate these deletions: replication for class I/II deletions through slipped mispairing between two repeats, and repair mainly for class II/III deletions mediated by mtDNA double-strand breaks. It seems possible that these two mechanisms work together as a powerful and complementary system to compensate for their defects in the generation of all these deletions, not respectively.

Large-scale mitochondrial DNA deletions in weak goslings

1. Evidence has accumulated in mammals to support the idea that mitochondrial DNA (mtDNA) deletions and mutations might contribute to ageing and reproductive failure. White Roman geese were monitored to evaluate the effect of large-scale deletions of mtDNA in an avian species. 2. A total of 340 samples from 114 dead embryos, 111 weak goslings, and 115 normal goslings were used in this experiment. The regions of these two large-scale mtDNA deletions, ΔmtDNA6829 and ΔmtDNA6992, were between the COI and ND5 genes. A 3·6% (4 out of 111) positive sample was detected in the weak goslings. In contrast, no large-scale mitochondrial DNA deletions were detected in either the dead embryos (0 out of 114) or the normal goslings (0 out of 115). 3. Large-scale mtDNA deletions may be a factor causing weak goslings.

Detection of single large-scale mitochondrial DNA deletions by MLPA technique

Detection of single large-scale mitochondrial DNA deletions by MLPA technique

Older mothers are not at risk of having grandchildren with sporadic mtDNA deletions

PurposeSingle large-scale mitochondrial DNA deletions account for a quarter of mitochondrial disease cases and occur sporadically with unknown risk factors. Mitochondrial DNA deletions accumulate with age in many tissues. Primordial germ cells, the precursors of oocytes are made by our grandmothers, therefore we wanted to determine whether age of maternal grandmother is a risk factor for sporadic mitochondrial DNA deletions. MethodsTwenty-nine patients with sporadic single mitochondrial DNA deletions from the Newcastle UK cohort provided dates of birth for mothers and maternal grandmothers plus father and paternal grandmother (healthy controls). ResultsMean age for grandmothers at birth of a mother of an affected patient was 28.5 years (SD ± 6.9) for single mitochondrial DNA deletions maternal grandmothers and 28.2 years (SD ± 6.1) for healthy control paternal grandmothers. ConclusionMaternal grandmother age is not a risk factor for sporadic mitochondrial DNA deletions, an important observation in a population where many women are delaying reproduction.

Sensory ataxic neuropathy with dysarthria and ophthalmoparesis (SANDO) in late life due to compound heterozygous POLG mutations

Missense mutations in the gene for polymerase gamma 1 (POLG1) cause a number of phenotypically heterogeneous mitochondrial diseases, most commonly progressive external ophthalmoplegia, and are characterized by the accumulation of multiple, large-scale deletions of mitochondrial DNA. The triad of sensory ataxic neuropathy, dysarthria, and ophthalmoparesis (SANDO) has been demonstrated in a small subset of patients with POLG1 mutations. We report a sporadic case of an 80-year-old compound heterozygote man who presented with SANDO and was found to have three known pathogenic mutations in the POLG1 gene (p.T251I/p.P587L/p.G848S). To our knowledge, none of these mutations have been demonstrated previously in SANDO. This patient's late presentation illustrates that a mitochondrial disorder should be considered regardless of age if the clinical symptoms warrant.

Resistance training in patients with single, large-scale deletions of mitochondrial DNA

Dramatic tissue variation in mitochondrial heteroplasmy has been found to exist in patients with sporadic mitochondrial DNA (mtDNA) mutations. Despite high abundance in mature skeletal muscle, levels of the causative mutation are low or undetectable in satellite cells. The activation of these typically quiescent mitotic cells and subsequent shifting of wild-type mtDNA templates to mature muscle have been proposed as a means of restoring a more normal mitochondrial genotype and function in these patients. Because resistance exercise is known to serve as a stimulus for satellite cell induction within active skeletal muscle, this study sought to assess the therapeutic potential of resistance training in eight patients with single, large-scale mtDNA deletions by assessing: physiological determinants of peak muscle strength and oxidative capacity and muscle biopsy-derived measures of damage, mtDNA mutation load, level of oxidative impairment and satellite cell numbers. Our results show that 12 weeks of progressive overload leg resistance training led to: (i) increased muscle strength; (ii) myofibre damage and regeneration; (iii) increased proportion of neural cell adhesion molecule (NCAM)-positive satellite cells; (iv) improved muscle oxidative capacity. Taken together, we believe these findings support the hypothesis of resistance exercise-induced mitochondrial gene-shifting in muscle containing satellite cells which have low or absent levels of deleted mtDNA. Further investigation is warranted to refine parameters of the exercise training protocol in order to maximize the training effect on mitochondrial genotype and treatment potential for patients with selected, sporadic mutations of mtDNA in skeletal muscle.

Genotype and phenotype analyses in 136 patients with single large-scale mitochondrial DNA deletions

We examined 136 patients with mitochondrial DNA (mtDNA) deletion. Clinical diagnoses included chronic progressive external ophthalmoplegia (94 patients); Kearns-Sayre syndrome (KSS; 33 patients); Pearson's marrow-pancreas syndrome (six patients); and Leigh syndrome, Reye-like syndrome, and mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (one patient). The length and location of deletion were highly variable. Only one patient had deletion within the so-called shorter arc between the two origins of mtDNA replication. The length of deletion and the number of deleted transfer ribonucleic acid (tRNAs) showed a significant relationship with age at onset. Furthermore, KSS patients had longer and larger numbers of deleted tRNAs, which could be risk factors for the systemic involvement of single mtDNA deletion diseases. We found 81 patterns of deletion. Direct repeats of 4 bp or longer flanking the breakpoints were found in 96 patients (70.5%) and those of 10 bp or longer in 49 patients (36.0%). We found two other common deletions besides the most common deletion (34 patients: 25.0%): the 2,310-bp deletion from nt 12113 to nt 14421 (11 patients: 8.0%) and the 7,664-bp deletion from nt 6330 to nt 13993 (ten patients: 7.3%). These deletions had incomplete direct repeats longer than 13 bp with one base mismatch.

Detection of mitochondrial DNA deletions in the cochlea and its structural elements from archival human temporal bone tissue

Large-scale deletions of mitochondrial DNA (mtDNA) have been associated with aging and disease in post-mitotic tissues. These post-mitotic tissues, including skeletal muscle, heart and brain, are heavily dependent on intact functional mitochondria. The cochlear tissues are known to contain an abundance of mitochondria. This observation stimulated a search for mtDNA deletions in the cochlea and its elements using a sensitive nested PCR methodology and long range PCR to explain the functional deficits observed in age-related hearing loss. The presence of the so-called “common” deletion (CD) was detected in cochlear tissue from two individuals with age-related hearing loss, 73 and 78 years of age. Three additional deletions, that to our knowledge have not been previously reported, were also identified in these two individuals, including a 5354bp deletion flanked with a 3bp repeat, a 9682bp deletion flanked by a 10bp repeat and a 5142bp deletion without a flanking repeat. The 9682 and 5142bp deletions were also detected in an individual 39 years of age with normal hearing, however, these two deletions were not detected in a normal hearing individual 9 years of age. In contrast, the 5354bp deletion was detected in all four of the individuals studied. To localize the deletions within the cochlea, the cochlear elements were removed by laser capture microdissection (LCM) and the mtDNA from these tissues was studied. The 5142 and 5354bp deletions were detected in the organ of corti, spiral ligament, and ganglion cells, but not in the stria vascularis. These findings correlate with the reduction in the number of spiral ganglion cells and outer hair cells, and the normal stria vascularis volume observed in this individual. All four of these deletions involve the cytochrome c oxidase (COX) subunit III gene, encoded by mtDNA. These observations suggest that multiple mtDNA deletions may contribute to a deficit in mitochondrial function in the cochlea and result in hearing loss if a level of physiological significance is reached.

439: Detection of large-scale deletions in mitochondrial DNA using DNA extracted from salivary samples

s / Journal of Clinical Neuroscience 15 (2008) 337–369 355 Results: Two of 35 (6%) patients had peri-operative strokes. Sixteen of 32 (50%) with post-operative imaging had new ischemic lesions including 5 of 6 with combined cardiac valve and CABG surgery. There were a range of 1–17 lesions, each <1 cm diameter except in 3 patients with large confluent areas of ischemia. Twenty of 29 (69%) patients with post-operative testing had significant cognitive declines in at least one domain (range 1–4), including all those with new ischemic lesions (p = 0.005). Conclusion: Brain injury is common following cardiac valve surgery: 6% have new neurological deficit and just over two thirds have measurable cognitive decline. Half of the patients had new post-operative ischemic lesions on DWI and these appeared embolic in nature. To our knowledge, this is the first study to link cognitive decline and cerebral ischemia. Cardiac surgery may be a useful model of human stroke in late phase IIB trials of putative neuroprotective therapies. doi:10.1016/j.jocn.2007.07.049 439: Detection of large-scale deletions in mitochondrial DNA using DNA extracted from salivary samples Himesha Vandebona , Con Yiannikas , Carolyn M. Sue ; Department of Neurogenetics, Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, Australia; Department of Neurology, Concord

Kearns-Sayre Syndrome Presenting as Complete Heart Block

Kearns-Sayre syndrome (KSS) is a rare mitochondrial disorder characterized by large-scale deletions of mitochondrial DNA. Neuromuscular and cardiac conduction systems are most commonly involved in these patients. Here, we discuss a 10-year-old patient with diabetes mellitus who presented in complete heart block leading to the diagnosis of KSS. The cardiovascular complications of this syndrome are reviewed and discussed.

The role of mitochondrial DNA large deletion for the development of presbycusis in Fischer 344 rats

Age-related hearing loss, or presbycusis, has been associated with large-scale mitochondrial DNA (mtDNA) deletion in previous studies. However, the role of this mtDNA damage in presbycusis is still not clear because the deletion in inner ears has not been measured quantitatively and analyzed in parallel with the time course of presbycusis. In the present study, the deletion was quantified using quantitative real-time PCR (qRT-PCR) in male Fischer 344 rats of different ages. It was found that the deletion increased quickly during young adulthood and reached over 60% at 6 months of age. However, a significant hearing loss was not seen until after 12 months of age. The results suggest that the existence of the deletion per se does not necessarily imply cochlear damage, but rather a critical level of the accumulated deletion seems to precede the hearing loss. The long delay may indicate the involvement of mechanisms other than mtDNA deletion in the development of presbycusis.

Differential diagnosis in ptosis and ophthalmoplegia: mitochondrial disease or myasthenia?

Sirs: One of the commonest phenotypes of mitochondrial disease is generalised fatigue with ptosis and a chronic progressive external ophthalmoplegia. The main differential diagnosis in these patients is with myasthenia gravis (MG). Ocular symptoms are the most common presentation of MG [1] and in up to 48% of patients are the only clinical manifestation [2]. Correct diagnosis is vital both to provide the best treatments and to avoid side effects from inappropriate ones [3]. We reviewed the records of 430 patients with proven mitochondrial disease on the basis of muscle histochemistry or mitochondrial DNA analysis to determine how many had originally been diagnosed with MG. Eighty-one of our patients had first presented with ptosis or ophthalmoplegia. Of these, a relatively small number, 15, had been investigated for possible MG as part of their diagnostic workup, and 5 (6.2%) had been given a primary diagnosis of MG. Table 1 shows the extra-ocular clinical features of the patients both at the time of diagnosis with MG and at subsequent diagnosis with mitochondrial disease. The average time between the initial diagnosis of MG and the subsequent diagnosis of mitochondrial disease was 3.6 years (range 1–9). Three of these patients had a single largescale deletion of mitochondrial DNA, and in two multiple deletions of the mitochondrial genome were found. All of the five patients initially diagnosed with MG had negative anti-acetylcholine receptor antibodies Table 2. Three patients were reported as having had a positive response to tensilon, although in one patient a repeat test was negative. Only three patients had undergone the more sensitive test of single fibre electromyography of orbicularis oculi. In one patient the initial result was reported as being consistent with myasthenia gravis on the basis of increased jitter (but with no blocking); this was subsequently repeated and reported as normal. All five patients had been treated with oral anticholinesterases. In one, an initial but shortlived symptomatic improvement was recorded. Three patients had received prolonged courses of oral steroids because of poor response to anticholinesterase treatment and one patient had undergone thymectomy. The differential diagnosis between mitochondrial disease presenting as ptosis and external ophthalmoplegia and myasthenia gravis can be difficult. The presenting clinical features of all the patients were entirely compatible with MG. Indeed, the majority reported variability in symptoms, often regarded as a hallmark of MG. Even those symptoms, which became apparent years later, such as proximal weakness and dysphagia, are common in MG. The investigations performed were similarly ambiguous; although all patients had negative anti-acetylcholine receptor antibodies, these are negative in up to 50% of ocular MG. Three had a positive tensilon test and one a suggestive single fibre EMG. Whilst all of these were probably false positives, an intriguing possibility is that these patients had disturbed neuromuscular transmission as a direct result of their mitochondrial disease. Blocking mitochondrial function in vitro leads to reduced phasic acetyl choline vesicle release [4] and changes in neuromuscular transmission similar to antibody mediated MG. Families with proven mitochondrial disease show minor but definite abnormalities on single fibre electromyography [5–7]. There are also anecdotal reports of symptomatic improvement in patients with mitochondrial disease given anticholinesterases [8], including one patient in this study. Although these drugs are as likely as any other to produce a placebo effect, these remain interesting observations. Our study emphasises the need to consider mitochondrial disease in the differential diagnosis of ocular MG, especially in those patients in whom symptoms do not respond well to treatment. R. G. Whittaker (&) AE A. M. Schaefer R. W. Taylor AE D. M. Turnbull Mitochondrial Research Group School of Neurology Neurobiology and Psychiatry University of Newcastle upon Tyne Newcastle upon Tyne NE2 4HH, UK Tel.: +1-91-2228334 Fax: +1-91-2228553 E-Mail: r.whittaker@ncl.ac.uk LETTER TO THE EDITORS J Neurol (2007) 254:1138– 1139 DOI 10.1007/s00415-006-0484-5

Mitochondrial DNA Deletion in a Child With Mitochondrial Encephalomyopathy, Growth Hormone Deficiency, and Hypoparathyroidism

We report an 11-year-old boy with short stature, bilateral ptosis, sensorineural hearing loss, muscle weakness, and endocrine abnormalities. Brain magnetic resonance imaging (MRI) showed a bilateral abnormal signal in the globus pallidus and in the midbrain tegment. Muscle biopsy specimens showed ragged red and cytochrome c oxidase negative fibers, and biochemical analysis of muscle homogenate showed a partial defect of complex I and IV activities of the respiratory chain enzymes. Analysis of mitochondrial DNA by a polymerase chain reaction screening procedure and Southern blot revealed a novel heteroplasmic single mitochondrial DNA deletion of 7.8 kb in different tissues. This deletion was absent in the blood DNA of his mother and brother. This case further expands and confirms the wide clinical spectrum of mitochondrial disorders associated with single large-scale mitochondrial DNA deletions.