Mutant mitochondrial helicase Twinkle causes multiple mtDNA deletions and a late-onset mitochondrial disease in mice

Mutations in the nuclear POLG1 gene compromise the integrity of mitochondrial DNA and show great allelic and clinical heterogeneity. Among adult POLG1-associated mitochondrial disease, the main clinical feature is chronic progressive external ophthalmoplegia. Other related clinical manifestations are sensory or cerebellar ataxia, peripheral neuropathy, myopathy or extrapyramidal symptoms. We report the case of a 72-year-old man who presented with a late onset sensory neuronopathy, chronic progressive external ophthalmoplegia, gait ataxia and parkinsonism. Genetic studies showed a compound heterozygosity of known pathogenic mutations in the POLG1 gene (variant T252I/P587 L in cis configuration in allele 1 and variant R807C in allele 2). Late life presentation highlights that mitochondrial disorders should be considered regardless of age of onset of symptoms.

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Clinicopathologic and molecular spectrum of RNASEH1-related mitochondrial disease

Neurology Genetics ◽

10.1212/nxg.0000000000000149 ◽

2017 ◽

Vol 3 (3) ◽

pp. e149 ◽

Cited By ~ 10

Author(s):

Enrico Bugiardini ◽

Olivia V. Poole ◽

Andreea Manole ◽

Alan M. Pittman ◽

Alejandro Horga ◽

...

Keyword(s):

Genetic Analysis ◽

Mitochondrial Disease ◽

Haplotype Analysis ◽

Progressive External Ophthalmoplegia ◽

Mtdna Deletions ◽

Clinical Presentations ◽

Human Rnase ◽

Disease Haplotype ◽

Founder Event ◽

Pathophysiologic Mechanisms

Objective:Pathologic ribonuclease H1 (RNase H1) causes aberrant mitochondrial DNA (mtDNA) segregation and is associated with multiple mtDNA deletions. We aimed to determine the prevalence of RNase H1 gene (RNASEH1) mutations among patients with mitochondrial disease and establish clinically meaningful genotype-phenotype correlations.Methods:RNASEH1 was analyzed in patients with (1) multiple deletions/depletion of muscle mtDNA and (2) mendelian progressive external ophthalmoplegia (PEO) with neuropathologic evidence of mitochondrial dysfunction, but no detectable multiple deletions/depletion of muscle mtDNA. Clinicopathologic and molecular evaluation of the newly identified and previously reported patients harboring RNASEH1 mutations was subsequently undertaken.Results:Pathogenic c.424G>A p.Val142Ile RNASEH1 mutations were detected in 3 pedigrees among the 74 probands screened. Given that all 3 families had Indian ancestry, RNASEH1 genetic analysis was undertaken in 50 additional Indian probands with variable clinical presentations associated with multiple mtDNA deletions, but no further RNASEH1 mutations were confirmed. RNASEH1-related mitochondrial disease was characterized by PEO (100%), cerebellar ataxia (57%), and dysphagia (50%). The ataxia neuropathy spectrum phenotype was observed in 1 patient. Although the c.424G>A p.Val142Ile mutation underpins all reported RNASEH1-related mitochondrial disease, haplotype analysis suggested an independent origin, rather than a founder event, for the variant in our families.Conclusions:In our cohort, RNASEH1 mutations represent the fourth most common cause of adult mendelian PEO associated with multiple mtDNA deletions, following mutations in POLG, RRM2B, and TWNK. RNASEH1 genetic analysis should also be considered in all patients with POLG-negative ataxia neuropathy spectrum. The pathophysiologic mechanisms by which the c.424G>A p.Val142Ile mutation impairs human RNase H1 warrant further investigation.

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Hybrid gel electrophoresis using skin fibroblasts to aid in diagnosing mitochondrial disease

Neurology Genetics ◽

10.1212/nxg.0000000000000336 ◽

2019 ◽

Vol 5 (3) ◽

pp. e336 ◽

Cited By ~ 1

Author(s):

Christopher Newell ◽

Aneal Khan ◽

David Sinasac ◽

John Shoffner ◽

Marisa W. Friederich ◽

...

Keyword(s):

Skeletal Muscle ◽

Muscle Biopsy ◽

Mitochondrial Disease ◽

Gel Electrophoresis ◽

Polyacrylamide Gel Electrophoresis ◽

Skin Fibroblasts ◽

Mtdna Deletions ◽

Transport Chain ◽

Long Range Pcr ◽

Blue Native

ObjectiveWe developed a novel, hybrid method combining both blue-native (BN-PAGE) and clear-native (CN-PAGE) polyacrylamide gel electrophoresis, termed BCN-PAGE, to perform in-gel activity stains on the mitochondrial electron transport chain (ETC) complexes in skin fibroblasts.MethodsFour patients aged 46–65 years were seen in the Metabolic Clinic at Alberta Children's Hospital and investigated for mitochondrial disease and had BN-PAGE or CN-PAGE on skeletal muscle that showed incomplete assembly of complex V (CV) in each patient. Long-range PCR performed on muscle-extracted DNA identified 4 unique mitochondrial DNA (mtDNA) deletions spanning the ATP6 gene of CV. We developed a BCN-PAGE method in skin fibroblasts taken from the patients at the same time and compared the findings with those in skeletal muscle.ResultsIn all 4 cases, BCN-PAGE in skin fibroblasts confirmed the abnormal CV activity found from muscle biopsy, suggesting that the mtDNA deletions involving ATP6 were most likely germline mutations that are associated with a clinical phenotype of mitochondrial disease.ConclusionsThe BCN-PAGE method in skin fibroblasts has a potential to be a less-invasive tool compared with muscle biopsy to screen patients for abnormalities in CV and other mitochondrial ETC complexes.

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

Acta Neuropathologica ◽

10.1007/s00401-011-0818-y ◽

2011 ◽

Vol 121 (6) ◽

pp. 775-783 ◽

Cited By ~ 20

Author(s):

Yusuke Sakiyama ◽

Yuji Okamoto ◽

Itsuro Higuchi ◽

Yukie Inamori ◽

Yoko Sangatsuda ◽

...

Keyword(s):

Mitochondrial Disease ◽

Late Onset

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Sporadic Inclusion Body Myositis: An Acquired Mitochondrial Disease with Extras

Biomolecules ◽

10.3390/biom9010015 ◽

2019 ◽

Vol 9 (1) ◽

pp. 15 ◽

Cited By ~ 3

Author(s):

Boel De Paepe

Keyword(s):

Inclusion Body ◽

Mitochondrial Disease ◽

Inclusion Body Myositis ◽

Late Onset ◽

Mitochondrial Dynamics ◽

Muscle Disorders ◽

Morphological Alterations ◽

Mitochondrial Alterations ◽

Sporadic Inclusion Body Myositis ◽

Mitochondrial Abnormality

The sporadic form of inclusion body myositis (IBM) is the most common late-onset myopathy. Its complex pathogenesis includes degenerative, inflammatory and mitochondrial aspects. However, which of those mechanisms are cause and which effect, as well as their interrelations, remain partly obscured to this day. In this review the nature of the mitochondrial dysregulation in IBM muscle is explored and comparison is made with other muscle disorders. Mitochondrial alterations in IBM are evidenced by histological and serum biomarkers. Muscular mitochondrial dynamics is disturbed, with deregulated organelle fusion leading to subsequent morphological alterations and muscle displays abnormal mitophagy. The tissue increases mitochondrial content in an attempt to compensate dysfunction, yet mitochondrial DNA (mtDNA) alterations and mild mtDNA depletion are also present. Oxidative phosphorylation defects have repeatedly been shown, most notably a reduction in complex IV activities and levels of mitokines and regulatory RNAs are perturbed. Based on the cumulating evidence of mitochondrial abnormality as a disease contributor, it is therefore warranted to regard IBM as a mitochondrial disease, offering a feasible therapeutic target to be developed for this yet untreatable condition.

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Late-onset respiratory failure due to TK2 mutations causing multiple mtDNA deletions

Neurology ◽

10.1212/01.wnl.0000436931.94291.e6 ◽

2013 ◽

Vol 81 (23) ◽

pp. 2051-2053 ◽

Cited By ~ 16

Author(s):

C. L. Alston ◽

A. M. Schaefer ◽

P. Raman ◽

N. Solaroli ◽

K. J. Krishnan ◽

...

Keyword(s):

Respiratory Failure ◽

Late Onset ◽

Mtdna Deletions

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Ultrasensitive deletion detection links mitochondrial DNA replication, disease, and aging

Genome Biology ◽

10.1186/s13059-020-02138-5 ◽

2020 ◽

Vol 21 (1) ◽

Cited By ~ 3

Author(s):

Scott A. Lujan ◽

Matthew J. Longley ◽

Margaret H. Humble ◽

Christopher A. Lavender ◽

Adam Burkholder ◽

...

Keyword(s):

Skeletal Muscle ◽

Mitochondrial Dna ◽

Dna Polymerase ◽

Late Onset ◽

Nuclear Gene ◽

Purifying Selection ◽

Pathogenic Variants ◽

Mtdna Deletions ◽

Fork Stalling ◽

Dna Polymerase Γ

Abstract Background Acquired human mitochondrial genome (mtDNA) deletions are symptoms and drivers of focal mitochondrial respiratory deficiency, a pathological hallmark of aging and late-onset mitochondrial disease. Results To decipher connections between these processes, we create LostArc, an ultrasensitive method for quantifying deletions in circular mtDNA molecules. LostArc reveals 35 million deletions (~ 470,000 unique spans) in skeletal muscle from 22 individuals with and 19 individuals without pathogenic variants in POLG. This nuclear gene encodes the catalytic subunit of replicative mitochondrial DNA polymerase γ. Ablation, the deleted mtDNA fraction, suffices to explain skeletal muscle phenotypes of aging and POLG-derived disease. Unsupervised bioinformatic analyses reveal distinct age- and disease-correlated deletion patterns. Conclusions These patterns implicate replication by DNA polymerase γ as the deletion driver and suggest little purifying selection against mtDNA deletions by mitophagy in postmitotic muscle fibers. Observed deletion patterns are best modeled as mtDNA deletions initiated by replication fork stalling during strand displacement mtDNA synthesis.

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