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Abstract
Mutations in the nuclear gene DGUOK, encoding deoxyguanosine kinase, cause an infantile hepatocerebral type of mitochondrial depletion syndrome (MDS). We report 6 MDS patients harboring bi-allelic DGUOK mutations, of which 3 are novel, including a large intragenic Austrian founder deletion. One patient was diagnosed with hepatocellular carcinoma aged 6 months, supporting a link between mitochondrial DNA depletion and tumorigenesis; liver transplantation proved beneficial with regard to both tumor treatment and psychomotor development.
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Fang W, Song P, Xie X, Wang J, Lu Y, Li G, Abuduxikuer K. A fatal case of mitochondrial DNA depletion syndrome with novel compound heterozygous variants in the deoxyguanosine kinase gene. Oncotarget 2017; 8:84309-84319. [PMID: 29137425 PMCID: PMC5663597 DOI: 10.18632/oncotarget.20905] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 08/17/2017] [Indexed: 12/02/2022] Open
Abstract
The deoxyguanosine kinase (DGUOK) gene controls mitochondrial DNA (mtDNA) maintenance, and variation in the gene can alter or abolish the anabolism of mitochondrial deoxyribonucleotides. A Chinese female infant, whose symptoms included weight stagnation, jaundice, hypoglycemia, coagulation disorders, abnormal liver function, and multiple abnormal signals in the brain, died at about 10 months old. Genetic testing revealed a compound heterozygote of alleles c.128T>C (p.I43T) and c.313C>T (p.R105*) of the DGUOK gene. c.128T>C (p.I43T) is a novel variant located in exon 1 (NM_080916) in the first beta sheet of DGUOK. Her mother was an allele c.313C>T (p.R105*) heterozygote, which is located in DGUOK exon 2 (NM_080916) between the third and fourth alpha helixes. c.313C>T (p.R105*) is predicted to result in a 173 amino acid residue truncation at the C terminus of DGUOK. There are as many as 112 infantile mtDNA depletion syndrome (MDS) cases in the literature related to DGUOK gene variants. These variants include missense mutations, nucleotide deletion, nucleotide insertion, and nucleotide duplication. Integrated data showed that mutations affected both conserved and non-conserved DGUOK amino acids and are associated with patient deaths.
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Affiliation(s)
- Weiyuan Fang
- The Center for Pediatric Liver Disease, Children's Hospital of Fudan University, Shanghai 201102, China
| | - Peng Song
- Advanced Training Program, Children's Hospital of Fudan University, Shanghai 201102, China.,Department of Infectious Diseases, Tangshan Maternal and Children Health Hospital, Tangshan City, Hebei Province 063000, China
| | - Xinbao Xie
- The Center for Pediatric Liver Disease, Children's Hospital of Fudan University, Shanghai 201102, China
| | - Jianshe Wang
- The Center for Pediatric Liver Disease, Children's Hospital of Fudan University, Shanghai 201102, China
| | - Yi Lu
- The Center for Pediatric Liver Disease, Children's Hospital of Fudan University, Shanghai 201102, China
| | - Gang Li
- Institute of Pediatrics, Children's Hospital of Fudan University, Shanghai 201102, China
| | - Kuerbanjiang Abuduxikuer
- The Center for Pediatric Liver Disease, Children's Hospital of Fudan University, Shanghai 201102, China
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Scheibye-Knudsen M, Croteau DL, Bohr VA. Mitochondrial deficiency in Cockayne syndrome. Mech Ageing Dev 2013; 134:275-83. [PMID: 23435289 PMCID: PMC3663877 DOI: 10.1016/j.mad.2013.02.007] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Revised: 01/24/2013] [Accepted: 02/08/2013] [Indexed: 01/05/2023]
Abstract
Cockayne syndrome is a rare inherited disorder characterized by accelerated aging, cachectic dwarfism and many other features. Recent work has implicated mitochondrial dysfunction in the pathogenesis of this disease. This is particularly interesting since mitochondrial deficiencies are believed to be important in the aging process. In this review, we discuss recent findings of mitochondrial pathology in Cockayne syndrome and suggest possible mechanisms for the mitochondrial dysfunction.
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Affiliation(s)
| | - Deborah L. Croteau
- Laboratory of Molecular Gerontology, National Institute on Aging, NIH, USA
| | - Vilhelm A. Bohr
- Laboratory of Molecular Gerontology, National Institute on Aging, NIH, USA
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El-Hattab AW, Scaglia F. Mitochondrial DNA depletion syndromes: review and updates of genetic basis, manifestations, and therapeutic options. Neurotherapeutics 2013; 10:186-98. [PMID: 23385875 PMCID: PMC3625391 DOI: 10.1007/s13311-013-0177-6] [Citation(s) in RCA: 157] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Mitochondrial DNA (mtDNA) depletion syndromes (MDS) are a genetically and clinically heterogeneous group of autosomal recessive disorders that are characterized by a severe reduction in mtDNA content leading to impaired energy production in affected tissues and organs. MDS are due to defects in mtDNA maintenance caused by mutations in nuclear genes that function in either mitochondrial nucleotide synthesis (TK2, SUCLA2, SUCLG1, RRM2B, DGUOK, and TYMP) or mtDNA replication (POLG and C10orf2). MDS are phenotypically heterogeneous and usually classified as myopathic, encephalomyopathic, hepatocerebral or neurogastrointestinal. Myopathic MDS, caused by mutations in TK2, usually present before the age of 2 years with hypotonia and muscle weakness. Encephalomyopathic MDS, caused by mutations in SUCLA2, SUCLG1, or RRM2B, typically present during infancy with hypotonia and pronounced neurological features. Hepatocerebral MDS, caused by mutations in DGUOK, MPV17, POLG, or C10orf2, commonly have an early-onset liver dysfunction and neurological involvement. Finally, TYMP mutations have been associated with mitochondrial neurogastrointestinal encephalopathy (MNGIE) disease that typically presents before the age of 20 years with progressive gastrointestinal dysmotility and peripheral neuropathy. Overall, MDS are severe disorders with poor prognosis in the majority of affected individuals. No efficacious therapy is available for any of these disorders. Affected individuals should have a comprehensive evaluation to assess the degree of involvement of different systems. Treatment is directed mainly toward providing symptomatic management. Nutritional modulation and cofactor supplementation may be beneficial. Liver transplantation remains controversial. Finally, stem cell transplantation in MNGIE disease shows promising results.
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Affiliation(s)
- Ayman W. El-Hattab
- />Division of Medical Genetics, Department of Pediatrics, The Children’s Hospital, King Fahad Medical City and Faculty of Medicine, King Saud bin Abdulaziz University for Health Science, Riyadh, Kingdom of Saudi Arabia
| | - Fernando Scaglia
- />Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, MS BCM225, Houston, TX 77030 USA
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Müller-Höcker J, Horvath R, Schäfer S, Hessel H, Müller-Felber W, Kühr J, Copeland WC, Seibel P. Mitochondrial DNA depletion and fatal infantile hepatic failure due to mutations in the mitochondrial polymerase γ (POLG) gene: a combined morphological/enzyme histochemical and immunocytochemical/biochemical and molecular genetic study. J Cell Mol Med 2011; 15:445-56. [PMID: 19538466 PMCID: PMC3822808 DOI: 10.1111/j.1582-4934.2009.00819.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2008] [Accepted: 05/06/2009] [Indexed: 11/27/2022] Open
Abstract
Combined morphological, immunocytochemical, biochemical and molecular genetic studies were performed on skeletal muscle, heart muscle and liver tissue of a 16-months boy with fatal liver failure. The pathological characterization of the tissues revealed a severe depletion of mtDNA (mitochondrial DNA) that was most pronounced in liver, followed by a less severe, but still significant depletion in skeletal muscle and the heart. The primary cause of the disease was linked to compound heterozygous mutations in the polymerase γ (POLG) gene (DNA polymerase γ; A467T, K1191N). We present evidence, that compound heterozygous POLG mutations lead to tissue selective impairment of mtDNA replication and thus to a mosaic defect pattern even in the severely affected liver. A variable defect pattern was found in liver, muscle and heart tissue as revealed by biochemical, cytochemical, immunocytochemical and in situ hybridization analysis. Functionally, a severe deficiency of cytochrome-c-oxidase (cox) activity was seen in the liver. Although mtDNA depletion was detected in heart and skeletal muscle, there was no cox deficiency in these tissues. Depletion of mtDNA and microdissection of cox-positive or negative areas correlated with the histological pattern in the liver. Interestingly, the mosaic pattern detected for cox-activity and mtDNA copy number fully aligned with the immunohistologically revealed defect pattern using Pol γ, mtSSB- and mtTFA-antibodies, thus substantiating the hypothesis that nuclear encoded proteins located within mitochondria become unstable and are degraded when they are not actively bound to mtDNA. Their disappearance could also aggravate the mtDNA depletion and contribute to the non-homogenous defect pattern.
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Affiliation(s)
- J Müller-Höcker
- Pathologisches Institut der Ludwig-Maximilians-Universität, München, Germany.
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6
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Collated mutations in mitochondrial DNA (mtDNA) depletion syndrome (excluding the mitochondrial gamma polymerase, POLG1). Biochim Biophys Acta Mol Basis Dis 2009; 1792:1109-12. [DOI: 10.1016/j.bbadis.2009.08.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2009] [Accepted: 08/27/2009] [Indexed: 01/09/2023]
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Ji JQ, Dimmock D, Tang LY, Descartes M, Gomez R, Rutledge SL, Schmitt ES, Wong LJ. A novel c.592-4_c.592-3delTT mutation in DGUOK gene causes exon skipping. Mitochondrion 2009; 10:188-91. [PMID: 19900589 DOI: 10.1016/j.mito.2009.11.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2009] [Revised: 10/29/2009] [Accepted: 11/03/2009] [Indexed: 10/20/2022]
Abstract
Deoxyguanosine kinase (DGUOK) catalyzes the first step of the mitochondrial deoxypurine salvage pathway, the phosphorylation of purine deoxyribonucleosides. Mutations in the DGUOK gene have been linked to inherited mtDNA depletion syndromes, neonatal liver failure, nystagmus, and hypotonia. Previously, we reported the first case of a heterozygous unclassified c.592-4_c.592-3delTT alteration in a patient with DGUOK deficiency without the demonstration of its pathogenicity (Dimmock et al., 2008). This alteration was predicted to cause aberrant splicing based upon two computer algorithms. We now report a homozygous c.592-4_c.592-3delTT mutation found in two affected siblings of asymptomatic consanguineous parents. The proband presented with symptoms of idiopathic hepatitis, liver dysfunction, nystagmus, and retinal blindness. This individual died at 6months of age due to liver failure. This individual's affected sibling presented similarly and has remarkable elevations of tyrosine, methionine, and alanine. Many organic acids were elevated in urine, including lactic acid, Krebs cycle intermediates, and para-hydroxy compounds; ketone bodies were also present. RNA studies support aberrant splicing. Sequencing of cDNA detected exon 5 skipping in the two affected siblings, but not in the normal control. These results indicate that the homozygous c.592-4_c.592-3delTT is deleterious and responsible for the DGUOK deficiency. The parents were subsequently confirmed to be carriers of this mutation. In summary, we have demonstrated that c.592-4_c.592-3delTT is a pathogenic splice acceptor site mutation leading to DGUOK deficiency.
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Affiliation(s)
- Jack Q Ji
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
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Wu C, Yan L, Depre C, Dhar SK, Shen YT, Sadoshima J, Vatner SF, Vatner DE. Cytochrome c oxidase III as a mechanism for apoptosis in heart failure following myocardial infarction. Am J Physiol Cell Physiol 2009; 297:C928-34. [PMID: 19625613 DOI: 10.1152/ajpcell.00045.2009] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cytochrome c oxidase (COX) is composed of 13 subunits, of which COX I, II, and III are encoded by a mitochondrial gene. COX I and II function as the main catalytic components, but the function of COX III is unclear. Because myocardial ischemia affects mitochondrial oxidative metabolism, we hypothesized that COX activity and expression would be affected during postischemic cardiomyopathy. This hypothesis was tested in a monkey model following myocardial infarction (MI) and subsequent pacing-induced heart failure (HF). In this model, COX I protein expression was decreased threefold after MI and fourfold after HF (P < 0.05 vs. sham), whereas COX II expression remained unchanged. COX III protein expression increased 5-fold after MI and further increased 10-fold after HF compared with sham (P < 0.05 vs. sham). The physiological impact of COX III regulation was examined in vitro. Overexpression of COX III in mitochondria of HL-1 cells resulted in an 80% decrease in COX I, 60% decrease in global COX activity, 60% decrease in cell viability, and threefold increase in apoptosis (P < 0.05). Oxidative stress induced by H2O2 significantly (P < 0.05) increased COX III expression. H2O2 decreased cell viability by 47 +/- 3% upon overexpression of COX III, but only by 12 +/- 5% in control conditions (P < 0.05). We conclude that ischemic stress in vivo and oxidative stress in vitro lead to upregulation of COX III, followed by downregulation of COX I expression, impaired COX oxidative activity, and increased apoptosis. Therefore, upregulation of COX III may contribute to the increased susceptibility to apoptosis following MI and subsequent HF.
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Affiliation(s)
- Changgong Wu
- Department of Cell Biology and Molecular Medicine and Cardiovascular Research Institute, Univeristy of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103, USA
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Dimmock DP, Dunn JK, Feigenbaum A, Rupar A, Horvath R, Freisinger P, Mousson de Camaret B, Wong LJ, Scaglia F. Abnormal neurological features predict poor survival and should preclude liver transplantation in patients with deoxyguanosine kinase deficiency. Liver Transpl 2008; 14:1480-5. [PMID: 18825706 DOI: 10.1002/lt.21556] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Deoxyguanosine kinase (DGUOK) deficiency is the commonest type of mitochondrial DNA depletion associated with a hepatocerebral phenotype. In this article, we evaluate predictors of survival and therapeutic options in patients with DGUOK deficiency. A systematic search of MEDLINE, LILAC, and SCIELO was carried out to identify peer-reviewed clinical trials, randomized controlled trials, meta-analyses, and other studies with clinical pertinence. DGUOK deficiency was searched with the terms dGK, DGUOK, mitochondrial DNA depletion, mtDNA, and hepatocerebral. Bibliographies of identified articles were reviewed for additional references. Thirteen identified studies met the inclusion criteria and were used in this study. The analysis revealed that DGUOK deficiency is associated with a variable clinical phenotype. Long-term survival is best predicted by the absence of profound hypotonia, significant psychomotor retardation, or nystagmus. In the presence of these features, there is increased mortality, and liver transplantation does not confer increased survival. In summary, liver transplantation appears to be futile in the presence of specific neurological signs or symptoms in patients affected with DGUOK deficiency. Conversely, in the absence of these neurological features, liver transplantation may be considered a potential treatment.
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Affiliation(s)
- David P Dimmock
- Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
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Mousson de Camaret B, Taanman JW, Padet S, Chassagne M, Mayençon M, Clerc-Renaud P, Mandon G, Zabot MT, Lachaux A, Bozon D. Kinetic properties of mutant deoxyguanosine kinase in a case of reversible hepatic mtDNA depletion. Biochem J 2007; 402:377-85. [PMID: 17073823 PMCID: PMC1798436 DOI: 10.1042/bj20060705] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
DGUOK [dG (deoxyguanosine) kinase] is one of the two mitochondrial deoxynucleoside salvage pathway enzymes involved in precursor synthesis for mtDNA (mitochondrial DNA) replication. DGUOK is responsible for the initial rate-limiting phosphorylation of the purine deoxynucleosides, using a nucleoside triphosphate as phosphate donor. Mutations in the DGUOK gene are associated with the hepato-specific and hepatocerebral forms of MDS (mtDNA depletion syndrome). We identified two missense mutations (N46S and L266R) in the DGUOK gene of a previously reported child, now 10 years old, who presented with an unusual revertant phenotype of liver MDS. The kinetic properties of normal and mutant DGUOK were studied in mitochondrial preparations from cultured skin fibroblasts, using an optimized methodology. The N46S/L266R DGUOK showed 14 and 10% residual activity as compared with controls with dG and deoxyadenosine as phosphate acceptors respectively. Similar apparent negative co-operativity in the binding of the phosphate acceptors to the wild-type enzyme was found for the mutant. In contrast, abnormal bimodal kinetics were shown with ATP as the phosphate donor, suggesting an impairment of the ATP binding mode at the phosphate donor site. No kinetic behaviours were found for two other patients with splicing defects or premature stop codon. The present study represents the first characterization of the enzymatic kinetic properties of normal and mutant DGUOK in organello and our optimized protocol allowed us to demonstrate a residual activity in skin fibroblast mitochondria from a patient with a revertant phenotype of MDS. The residual DGUOK activity may play a crucial role in the phenotype reversal.
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Oldfors A, Tulinius M. Mitochondrial encephalomyopathies. HANDBOOK OF CLINICAL NEUROLOGY 2007; 86:125-165. [PMID: 18808998 DOI: 10.1016/s0072-9752(07)86006-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
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Alberio S, Mineri R, Tiranti V, Zeviani M. Depletion of mtDNA: syndromes and genes. Mitochondrion 2006; 7:6-12. [PMID: 17280874 DOI: 10.1016/j.mito.2006.11.010] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2006] [Accepted: 10/06/2006] [Indexed: 11/23/2022]
Abstract
Maintenance of mitochondrial DNA (mtDNA) requires the concerted activity of several nuclear-encoded factors that participate in its replication, being part of the mitochondrial replisome or ensuring the balanced supply of dNTPs to mitochondria. In the past decade, a growing number of syndromes associated with dysfunction due to tissue-specific depletion of mtDNA (MDS) have been reported. This article reviews the current knowledge of the genes responsible for these disorders, the impact of different mutations in the epidemiology of MDS and their role in the pathogenic mechanisms underlying the different clinical presentations.
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Affiliation(s)
- Simona Alberio
- Unit of Molecular Neurogenetics-Pierfranco and Luisa Mariani Center for the Study of Children's Mitochondrial Disorders, C. Besta Neurological Institute Foundation, IRCCS, Italy
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Carinci F, Piattelli A, Guida L, Perrotti V, Laino G, Oliva A, Annunziata M, Palmieri A, Pezzetti F. Effects of Emdogain on osteoblast gene expression. Oral Dis 2006; 12:329-42. [PMID: 16700745 DOI: 10.1111/j.1601-0825.2005.01204.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
OBJECTIVE Emdogain (EMD) is a protein extract purified from porcine enamel and has been introduced in clinical practice to obtain periodontal regeneration. EMD is composed mainly of amelogenins (90%), while the remaining 10% is composed of non-amelogenin enamel matrix proteins such as enamelins, tuftelin, amelin and ameloblastin. Enamel matrix proteins seem to be involved in root formation. EMD has been reported to promote proliferation, migration, adhesion and differentiation of cells associated with healing periodontal tissues in vivo. DESIGN How this protein acts on osteoblasts is poorly understood. We therefore attempted to address this question by using a microarray technique to identify genes that are differently regulated in osteoblasts exposed to enamel matrix proteins. RESULTS By using DNA microarrays containing 20,000 genes, we identified several upregulated and downregulated genes in the osteoblast-like cell line (MG-63) cultured with enamel matrix proteins (Emd). The differentially expressed genes cover a broad range of functional activities: (i) signaling transduction, (ii) transcription, (iii) translation, (iv) cell cycle regulation, proliferation and apoptosis, (v) immune system, (vi) vesicular transport and lysosome activity, and (vii) cytoskeleton, cell adhesion and extracellular matrix production. CONCLUSIONS The data reported are the first genome-wide scan of the effect of enamel matrix proteins on osteoblast-like cells. These results can contribute to our understanding of the molecular mechanisms of bone regeneration and as a model for comparing other materials with similar clinical effects.
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Affiliation(s)
- F Carinci
- Department of Maxillofacial Surgery, University of Ferrara, Ferrara, Italy
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Nguyen KV, Sharief FS, Chan SSL, Copeland WC, Naviaux RK. Molecular diagnosis of Alpers syndrome. J Hepatol 2006; 45:108-16. [PMID: 16545482 DOI: 10.1016/j.jhep.2005.12.026] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2005] [Revised: 12/01/2005] [Accepted: 12/02/2005] [Indexed: 01/18/2023]
Abstract
BACKGROUND/AIMS Alpers syndrome is a developmental mitochondrial DNA depletion syndrome leading to fatal brain and liver disease in children and young adults. Mutations in the gene for the mitochondrial DNA polymerase (POLG) have recently been shown to cause this disorder. METHODS The POLG locus was sequenced in 15 sequential probands diagnosed with Alpers syndrome. In addition, the POLG mutations found to cause Alpers syndrome in the 20 cases published to date were analyzed. RESULTS POLG DNA testing accurately diagnosed 87% (13/15=87%: 95% confidence interval=60-98%) of cases. Five new POLG amino acid substitutions (F749S, R852C, T914P, L966R, and L1173fsX) were found that were associated with Alpers syndrome in five unrelated kindreds, and 14 different allelic combinations of POLG mutations were found to cause Alpers syndrome in the 20 probands published to date. The most common Alpers-causing mutation was the A467T substitution, located in the linker region of the pol gamma protein, which accounted for about 40% of the alleles and was present in 65% of the patients. All patients with POLG mutations had either the A467T or the W748S substitution in the linker region. CONCLUSIONS Screening for A467T and W748S substitutions in POLG now constitutes the most rapid and sensitive test available for confirming the clinical diagnosis of Alpers syndrome.
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Affiliation(s)
- Khue V Nguyen
- Department of Medicine, University of California, San Diego School of Medicine, 214 Dickinson Street, Bldg. CTF, Rm. C-103, San Diego, CA 92103-8467, USA
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15
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Galbiati S, Bordoni A, Papadimitriou D, Toscano A, Rodolico C, Katsarou E, Sciacco M, Garufi A, Prelle A, Aguennouz M', Bonsignore M, Crimi M, Martinuzzi A, Bresolin N, Papadimitriou A, Comi GP. New mutations in TK2 gene associated with mitochondrial DNA depletion. Pediatr Neurol 2006; 34:177-85. [PMID: 16504786 DOI: 10.1016/j.pediatrneurol.2005.07.013] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Revised: 06/14/2005] [Accepted: 07/11/2005] [Indexed: 11/17/2022]
Abstract
Mitochondrial deoxyribonucleic acid depletion syndromes are autosomal recessive disorders characterized by a reduction of the amount of mitochondrial deoxyribonucleic acid, which impairs the synthesis of respiratory chain complexes. Mutations in the deoxyguanosine kinase and polymerase gamma genes have been identified in hepatocerebral forms, whereas thymidine kinase 2 gene mutations have been found in patients with isolated myopathy, encephalomyopathy, or spinal muscular atrophy. Mutations in the gene encoding the beta subunit of the adenosine diphosphate-forming succinyl-coenzyme A synthetase have also been reported in a family. In this report, the clinical, molecular, morphologic, and biochemical features of five children from two independent families with an infantile encephalomyopathy are characterized. The affected children manifested muscle mitochondrial deoxyribonucleic acid depletion and three novel thymidine kinase 2 gene mutations. They consist of a homozygous substitution resulting in Ala to Val change at the highly conserved position 181 of thymidine kinase in the first family, and two heterozygous substitutions in the second family: a Cys to Trp change at residue 108 and a Leu to Pro change at residue 257 of the enzyme. Common clinical features associated with these TK2 mutations are a normal early developmental phase followed by psychomotor regression, encephalopathy often with epileptic seizures, and myopathy with features of a progressive dystrophic process.
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Affiliation(s)
- Sara Galbiati
- Centro Dino Ferrari, Department of Neurological Sciences, University of Milan, I.R.C.C.S. Ospedale Maggiore Policlinico, Milano, Italy.
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Carrozzo R, Wittig I, Santorelli FM, Bertini E, Hofmann S, Brandt U, Schägger H. Subcomplexes of human ATP synthase mark mitochondrial biosynthesis disorders. Ann Neurol 2005; 59:265-75. [PMID: 16365880 DOI: 10.1002/ana.20729] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE METHODS We describe biochemically and clinically relevant aspects of mitochondrial ATP synthase, the enzyme that supplies most ATP for the cells energy demand. RESULTS Analyzing human Rho zero cells we could identify three subcomplexes of ATP synthase: F1 catalytic domain, F1 domain with bound natural IF1 inhibitor protein, and F1-c subcomplex, an assembly of F1 domain and a ring of F(O)-subunits c. Large amounts of F1 subcomplexes accumulated also in mitochondria of patients with specific mitochondrial disorders. By quantifying the F1 subcomplexes and other oxidative phosphorylation complexes in parallel, we were able to discriminate three classes of defects in mitochondrial biosynthesis, namely, mitochondrial DNA depletion, mitochondrial transfer RNA (tRNA) mutations, and mutations in the mitochondrial ATP6 gene. INTERPRETATION The relatively simple electrophoretic assay used here is a straightforward approach to differentiate between various types of genetic alterations affecting the biosynthesis of oxidative phosphorylation complexes and will be useful to guide molecular genetic diagnostics in the field of mitochondrial neuromuscular disorders.
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Affiliation(s)
- Rosalba Carrozzo
- Unit of Molecular Medicine, Bambino Gesù Hospital and Research Institute, Rome, Italy
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Slama A, Giurgea I, Debrey D, Bridoux D, de Lonlay P, Levy P, Chretien D, Brivet M, Legrand A, Rustin P, Munnich A, Rötig A. Deoxyguanosine kinase mutations and combined deficiencies of the mitochondrial respiratory chain in patients with hepatic involvement. Mol Genet Metab 2005; 86:462-5. [PMID: 16263314 DOI: 10.1016/j.ymgme.2005.09.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/14/2005] [Revised: 09/13/2005] [Accepted: 09/13/2005] [Indexed: 10/25/2022]
Abstract
The activity of deoxyguanosine kinase (DGUOK), a mitochondrial enzyme involved in the anabolism of mitochondrial (mt) deoxyribonucleotides, governs the maintenance of the mtDNA. Deleterious mutations of the DGUOK gene are thus associated with mtDNA depletion and result in combined deficiencies of mtDNA-encoded respiratory chain enzymes. With the aim to estimate the prevalence of DGUOK mutations in a cohort of 30 patients with hepatocerebral disease and combined respiratory chain deficiencies, we studied the DGUOK gene and identified previously unreported mutations in five families. Two patients and their affected sibs, born to non-consanguineous parents, were homozygous for a missense mutation (M1T, and L250S, respectively). One patient presented a homozygous 4 pb insertion (796 insTGAT) and two other patients, and their affected sibs, were compound heterozygous (E165V/L266R and E211G/L266R, respectively). These findings allowed us to propose prenatal diagnosis in two families. In conclusion, we observed a high prevalence of DGUOK mutations (17%) in patients with hepatic involvement and combined respiratory chain deficiencies with hepatic involvement.
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Affiliation(s)
- A Slama
- Laboratoire de Biochimie 1, APHP, hôpital de Bicêtre, Le Kremlin-Bicêtre, France.
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18
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Labarthe F, Dobbelaere D, Devisme L, De Muret A, Jardel C, Taanman JW, Gottrand F, Lombès A. Clinical, biochemical and morphological features of hepatocerebral syndrome with mitochondrial DNA depletion due to deoxyguanosine kinase deficiency. J Hepatol 2005; 43:333-41. [PMID: 15964659 DOI: 10.1016/j.jhep.2005.03.023] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Revised: 03/10/2005] [Accepted: 03/14/2005] [Indexed: 12/04/2022]
Abstract
BACKGROUND/AIMS The aim of this study was to delineate the specific clinical, biological and liver morphological alterations of the hepatocerebral syndrome due to alterations in the deoxyguanosine kinase gene, a rare and severe form of mitochondrial DNA depletion syndrome. METHODS We report seven cases from three unrelated families with the same mutation in the deoxyguanosine kinase gene. RESULTS All the patients presented in the first weeks of life with hepatomegaly and progressive liver failure that led to death few months later. Major psychomotor delay and multidirectional nystagmus were reported shortly after onset of the disease. Severe hyperlactacidaemia was constant. Histological examination of the liver disclosed a multifocal injury of hepatocytes with irregular foamy steatosis, cholestasis, and fibrosis, associated with different degrees of hepatosiderosis and glycogen depletion. Liver respiratory chain activities were abnormal in all analysed patients and the amount of liver mitochondrial DNA was severely decreased. An identical homozygous 4bp GATT duplication was identified in the deoxyguanosine kinase gene of all the cases. CONCLUSIONS These patients, together with patients reported in the literature, permit to delineate the specific features of the hepatocerebral form of mitochondrial DNA depletion syndrome and to differentiate them from other causes of neonatal liver failure.
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Affiliation(s)
- François Labarthe
- Groupement de Médecine Pédiatrique, Hôpital Clocheville, CHU Tours, France
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19
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Taanman JW, Llewelyn Williams S. The Human Mitochondrial Genome. OXIDATIVE STRESS AND DISEASE 2005. [DOI: 10.1201/9781420028843.ch3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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20
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Abstract
Mitochondrial DNA (mtDNA) depends on numerous nuclear encoded factors and a constant supply of deoxyribonucleoside triphosphates (dNTP), for its maintenance and replication. The function of proteins involved in nucleotide metabolism is perturbed in a heterogeneous group of disorders associated with depletion, multiple deletions, and mutations of the mitochondrial genome. Disturbed homeostasis of the mitochondrial dNTP pools are likely the underlying cause. Understanding of the biochemical and molecular basis of these disorders will promote the development of new therapeutic approaches. This article reviews the current knowledge of deoxyribonucleotide metabolism in relation to disorders affecting mtDNA integrity.
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Affiliation(s)
- Ann Saada
- Metabolic Disease Unit, Shaare Zedek Medical Center, Jerusalem, Israel.
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21
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Saada-Reisch A. Deoxyribonucleoside kinases in mitochondrial DNA depletion. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2005; 23:1205-15. [PMID: 15571232 DOI: 10.1081/ncn-200027480] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Mitochondrial DNA (mtDNA) depletion syndromes (MDS) are a heterogeneous group of mitochondrial disorders, manifested by a decreased mtDNA copy number and respiratory chain dysfunction. Primary MDS are inherited autosomally and may affect a single organ or multiple tissues. Mutated mitochondrial deoxyribonucleoside kinases; deoxyguanosine kinase (dGK) and thymidine kinase 2 (TK2), were associated with the hepatocerebral and myopathic forms of MDS respectively. dGK and TK2 are key enzymes in the mitochondrial nucleotide salvage pathway, providing the mitochondria with deoxyribonucleotides (dNP) essential for mtDNA synthesis. Although the mitochondrial dNP pool is physically separated from the cytosolic one, dNP's may still be imported through specific transport. Non-replicating tissues, where cytosolic dNP supply is down regulated, are thus particularly vulnerable to dGK and TK2 deficiency. The overlapping substrate specificity of deoxycytidine kinase (dCK) may explain the relative sparing of muscle in dGK deficiency, while low basal TK2 activity render this tissue susceptible to TK2 deficiency. The precise pathophysiological mechanisms of mtDNA depletion due to dGK and TK2 deficiencies remain to be determined, though recent findings confirm that it is attributed to imbalanced dNTP pools.
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Affiliation(s)
- Ann Saada-Reisch
- Metabolic Disease Unit, Shaare Zedek Medical Center, Jerusalem, Israel
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22
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Janssen RJRJ, van den Heuvel LP, Smeitink JAM. Genetic defects in the oxidative phosphorylation (OXPHOS) system. Expert Rev Mol Diagn 2004; 4:143-56. [PMID: 14995902 DOI: 10.1586/14737159.4.2.143] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The oxidative phosphorylation (OXPHOS) system consists of five multiprotein complexes and two mobile electron carriers embedded in the lipid bilayer of the mitochondrial inner membrane. With the exception of complex II and the mobile carriers, the other parts of the OXPHOS system are under dual genetic control. Due to this bigenomic control, the inheritance of OXPHOS system defects is either maternal, in the case of mitochondrial DNA mutations, autosomal or X-linked, in the case of nuclear gene defects. In this review, our current genetic understanding of OXPHOS system enzyme deficiencies will be summarized, and future directions that the field might take to unravel so-far genetically unresolved OXPHOS system enzyme deficiencies will be described, with special emphasis on complex I biogenesis.
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Affiliation(s)
- Rolf J R J Janssen
- University Medical Center Nijmegen, NCMD, Department of Pediatrics, PO Box 9101, 6500 HB Nijmegen, The Netherlands
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23
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Wang L, Eriksson S. Mitochondrial deoxyguanosine kinase mutations and mitochondrial DNA depletion syndrome. FEBS Lett 2003; 554:319-22. [PMID: 14623087 DOI: 10.1016/s0014-5793(03)01181-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Mitochondrial deoxyguanosine kinase (dGK) catalyzes the initial phosphorylation of purine deoxynucleosides. Mutations in the dGK gene leading to deficiency in dGK activity is one of the causes of severe mitochondrial DNA depletion diseases. We used site-directed mutagenesis to introduce the clinically observed genetic alterations in the dGK gene and characterized the recombinant enzymes. The R142K enzyme had very low activity with deoxyguanosine and no activity with deoxyadenosine. The E227K mutant enzyme had unchanged K(m) values for all its substrates but very low V(max) values. C-terminal truncated dGK proteins were inactive. These results may help to define the role of dGK in mitochondrial DNA (mtDNA) precursor synthesis.
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Affiliation(s)
- Liya Wang
- Department of Molecular Biosciences, Section of Veterinary Medical Biochemistry, SLU, The Biomedical Centre, P.O. Box 575, SE-751 23 Uppsala, Sweden.
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24
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Taanman JW, Muddle JR, Muntau AC. Mitochondrial DNA depletion can be prevented by dGMP and dAMP supplementation in a resting culture of deoxyguanosine kinase-deficient fibroblasts. Hum Mol Genet 2003; 12:1839-45. [PMID: 12874104 DOI: 10.1093/hmg/ddg192] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Deoxyguanosine kinase is a constitutively expressed, mitochondrial enzyme of the deoxyribonucleoside salvage pathway. Deficiency of deoxyguanosine kinase causes early-onset, hepatocerebral mitochondrial DNA (mtDNA) depletion syndrome. To clarify the molecular mechanism of the disease, a skin fibroblast culture was studied from a patient carrying a homozygous nonsense mutation in the gene for deoxyguanosine kinase. In situ examination of DNA synthesis demonstrated that, although mtDNA synthesis is cell cycle independent in control fibroblasts, mtDNA synthesis occurs mainly during the S-phase in deoxyguanosine kinase-deficient cells. Consistent with this observation, it was found that the mtDNA content of exponentially growing, deoxyguanosine kinase-deficient cells is only mildly affected. When cycling is inhibited by serum-deprivation and cells are in a resting state, however, the mtDNA content drops considerably in deoxyguanosine kinase-deficient cells, yet remains stable in control fibroblasts. The decline in mtDNA content in resting, deoxyguanosine kinase-deficient cells can be prevented by dGMP and dAMP supplementation, providing conclusive evidence that substrate limitation triggers mtDNA depletion in deoxyguanosine kinase-deficient cells.
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Affiliation(s)
- Jan-Willem Taanman
- University Department of Clinical Neurosciences, Royal Free and University College Medical School, University College London, Rowland Hill Street, London NW3 2PF, UK.
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25
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Abstract
Mitochondrial DNA (mtDNA) depletion is associated with heterogeneous clinical phenotypes. The recent identification of the mutated genes in three groups of patients with mtDNA depletion had underscored the importance of the synthetic pathway of the mitochondrial nucleotides for mtDNA replication. Future goals include understanding how the defective proteins perturb replication, why it affects only some tissues and spares others, and which other genes should be considered in other patients with mtDNA depletion.
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Affiliation(s)
- Orly Elpeleg
- The Metabolic Disease Unit, Shaare-Zedek Medical Center, Jerusalem 91031, Israel.
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26
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Abstract
Mitochondrial encephalomyopathies are diseases caused by defective oxidative phosphorylation (OXPHOS), and affect the nervous system and/or skeletal muscle. They have emerged as a major entity among the neurometabolic diseases of childhood with an incidence of 1 in 11,000 children, and also have a high prevalence in adults. The first pathogenic mutation of human mitochondrial DNA (mtDNA) was discovered in 1988. Since then more than 100 mutations of mtDNA have been reported, including point mutations of genes encoding transfer RNA, ribosomal RNA, and proteins, as well as large-scale deletions. The first nuclear-DNA gene mutation causing OXPHOS disease was described in 1995. Mutations in nuclear genes may affect the respiratory chain by various mechanisms. Pathogenic mutations of nuclear-DNA-encoded subunits of complex I and II have been demonstrated as have mutations of respiratory chain assembly proteins. Several nuclear genes associated with mtDNA maintenance have been found to be associated with mitochondrial disorders since mutations in these genes predispose to multiple mtDNA deletions and/or reduced copy number of mtDNA. The genotype-phenotype correlation is not yet entirely clear, but new animal models will enhance our ability to study the pathophysiology of OXPHOS disorders.
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Affiliation(s)
- Anders Oldfors
- Department of Pathology, Sahlgrenska University Hospital, Goteborg, Sweden.
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