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Berit Woldseth - One of the best experts on this subject based on the ideXlab platform.
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Succinate-CoA ligase deficiency due to mutations in SUCLA2 and SUCLG1: phenotype and genotype correlations in 71 patients
Journal of Inherited Metabolic Disease, 2016Co-Authors: Rosalba Carrozzo, Daniela Verrigni, Magnhild Rasmussen, Hernan Amartino, Marzia Bianchi, Daniela Buhas, Samir Mesli, Karin Naess, Alfred Peter Born, Berit WoldsethAbstract:Background The encephalomyopathic mtDNA depletion syndrome with methylmalonic aciduria is associated with deficiency of succinate-CoA ligase, caused by mutations in SUCLA2 or SUCLG1 . We report here 25 new patients with succinate-CoA ligase deficiency, and review the clinical and molecular findings in these and 46 previously reported patients. Patients and results Of the 71 patients, 50 had SUCLA2 mutations and 21 had SUCLG1 mutations. In the newly-reported 20 SUCLA2 patients we found 16 different mutations, of which nine were novel: two large gene deletions, a 1 bp duplication, two 1 bp deletions, a 3 bp insertion, a nonsense mutation and two missense mutations. In the newly-reported SUCLG1 patients, five missense mutations were identified, of which two were novel. The median onset of symptoms was two months for patients with SUCLA2 mutations and at birth for SUCLG1 patients. Median survival was 20 years for SUCLA2 and 20 months for SUCLG1 . Notable clinical differences between the two groups were hepatopathy, found in 38 % of SUCLG1 cases but not in SUCLA2 cases, and hypertrophic cardiomyopathy which was not reported in SUCLA2 patients, but documented in 14 % of cases with SUCLG1 mutations. Long survival, to age 20 years or older, was reported in 12 % of SUCLA2 and in 10 % of SUCLG1 patients. The most frequent abnormality on neuroimaging was basal ganglia involvement, found in 69 % of SUCLA2 and 80 % of SUCLG1 patients. Analysis of respiratory chain enzyme activities in muscle generally showed a combined deficiency of complexes I and IV, but normal histological and biochemical findings in muscle did not preclude a diagnosis of succinate-CoA ligase deficiency. In five patients, the urinary excretion of methylmalonic acid was only marginally elevated, whereas elevated plasma methylmalonic acid was consistently found. Conclusions To our knowledge, this is the largest study of patients with SUCLA2 and SUCLG1 deficiency. The most important findings were a significantly longer survival in patients with SUCLA2 mutations compared to SUCLG1 mutations and a trend towards longer survival in patients with missense mutations compared to loss-of-function mutations. Hypertrophic cardiomyopathy and liver involvement was exclusively found in patients with SUCLG1 mutations, whereas epilepsy was much more frequent in patients with SUCLA2 mutations compared to patients with SUCLG1 mutations. The mutation analysis revealed a number of novel mutations, including a homozygous deletion of the entire SUCLA2 gene, and we found evidence of two founder mutations in the Scandinavian population, in addition to the known SUCLA2 founder mutation in the Faroe Islands.
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succinate coa ligase deficiency due to mutations in sucla2 and SUCLG1 phenotype and genotype correlations in 71 patients
Journal of Inherited Metabolic Disease, 2016Co-Authors: Rosalba Carrozzo, Daniela Verrigni, Magnhild Rasmussen, Hernan Amartino, Marzia Bianchi, Daniela Buhas, Samir Mesli, Karin Naess, Alfred Peter Born, Berit WoldsethAbstract:Background The encephalomyopathic mtDNA depletion syndrome with methylmalonic aciduria is associated with deficiency of succinate-CoA ligase, caused by mutations in SUCLA2 or SUCLG1. We report here 25 new patients with succinate-CoA ligase deficiency, and review the clinical and molecular findings in these and 46 previously reported patients.
Leejun C Wong - One of the best experts on this subject based on the ideXlab platform.
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Phenotypic variability in deficiency of the α subunit of succinate-CoA ligase.
JIMD reports, 2019Co-Authors: Didem Demirbas, Leejun C Wong, David J. Harris, Xiaoping Huang, Susan E. Waisbren, Irina Anselm, Jordan P. Lerner‐ellis, Harvey L. Levy, Gerard T. BerryAbstract:: Succinyl-CoA synthetase or succinate-CoA ligase deficiency can result from biallelic mutations in SUCLG1 gene that encodes for the alpha subunit of the succinyl-CoA synthetase. Mutations in this gene were initially associated with fatal infantile lactic acidosis. We describe an individual with a novel biallelic pathogenic mutation in SUCLG1 with a less severe phenotype dominated by behavioral problems. The mutation was identified to be c.512A>G corresponding to a p.Asn171Ser change in the protein. The liquid chromatography tandem mass spectrometry-based enzyme activity assay on cultured fibroblasts revealed a markedly reduced activity of succinyl-CoA synthetase enzyme when both ATP and GTP were substrates, affecting both ADP-forming and GDP-forming functions of the enzyme.
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Next generation sequencing of patients with mut methylmalonic aciduria: Validation of somatic cell studies and identification of 16 novel mutations.
Molecular Genetics and Metabolism, 2016Co-Authors: Mihaela Pupavac, Victor Wei Zhang, Jing Wang, Xia Tian, Yanming Feng, Stella Chen, Remington Fenter, David Watkins, Leejun C WongAbstract:Abstract Mutations in the MUT gene, which encodes the mitochondrial enzyme methylmalonyl-CoA mutase, are responsible for the mut form of methylmalonic aciduria (MMA). In this study, a next generation sequencing (NGS) based gene panel was used to analyze 53 patients that had been diagnosed with mut MMA by somatic cell complementation analysis. A total of 54 different mutations in MUT were identified in 48 patients; 16 novel mutations were identified, including 1 initiation site mutation (c.2T>C [p.M1?]), 1 missense mutation (c.566A>T [p.N189I]), 2 nonsense mutations (c.129G>A [p.W43*] and c.1975C>T [p.Q659*]), 2 mutations affecting splice sites (c.753+3A>G and c.754-2A>G), 8 small insertions, deletions, and duplications (c.29dupT [p.L10Ffs*39], c.55dupG [p.V19Gfs*30], c.631_633delGAG [p.E211del], c.795_796insT [p.M266Yfs*7], c.1061delCinsGGA [p.S354Wfs*20], c.1065_1068dupATGG [p.S357Mfs*5], c.1181dupT [p.L394Ffs*30], c.1240delG [p.E414Kfs*17]), a large insertion (c.146_147ins279), and a large deletion involving exon 13. Phenotypic rescue and cDNA analysis were used to confirm that the c.146_147ins279 and c.631_633delGAG mutations were associated with the decreased methylmalonyl-CoA mutase function observed in the patient fibroblasts. In five patients, the NGS panel did not confirm the diagnosis made by complementation analysis. One of these patients was found to carry 2 novel mutations (c.433G > A [p.E145K] and c.511A>C [p.N171H]) in the SUCLG1 gene.
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a SUCLG1 mutation in a patient with mitochondrial dna depletion and congenital anomalies
Molecular genetics and metabolism reports, 2014Co-Authors: Megan Landsverk, Victor Wei Zhang, Leejun C Wong, Hans C AnderssonAbstract:Abstract Defects in two subunits of succinate-CoA ligase encoded by the genes SUCLG1 and SUCLA2 have been identified in mitochondrial DNA (mtDNA) depletion syndromes. Patients generally present with encephalomyopathy and mild methylmalonic acidemia (MMA), however mutations in SUCLG1 normally appear to result in a more severe clinical phenotype. In this report, we describe a patient with fatal infantile lactic acidosis and multiple congenital anomalies (MCAs) including renal and cardiac defects. Molecular studies showed a defective electron transport chain (ETC), mtDNA depletion, and a novel homozygous mutation in the SUCLG1 gene. Although our patient's clinical biochemical phenotype is consistent with a SUCLG1 mutation, it is unclear whether the MCAs observed in our patient are a result of the SUCLG1 mutation or alterations in a second gene. An increasing number of reports have described MCAs associated with mitochondrial disorders and SUCLG1 specifically. Additional studies such as whole exome sequencing will further define whether additional genes are responsible for the observed MCAs.
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fatal infantile lactic acidosis and a novel homozygous mutation in the SUCLG1 gene a mitochondrial dna depletion disorder
Molecular Genetics and Metabolism, 2011Co-Authors: Linda M Randolph, Leejun C Wong, Hollie A Jackson, Jing Wang, Hiroyuki Shimada, Pedro A Sanchezlara, Derek Wong, Richard G BolesAbstract:Abstract Mitochondrial DNA (mtDNA) depletion syndromes are autosomal recessive conditions in which the mtDNA copy number is greatly decreased in affected tissues. The encephalomyopathic group of these syndromes comprise mutations in SUCLA2 and SUCLG1 subunits [1]. In this report, we describe a patient with fatal infantile lactic acidosis associated with mutations in the SUCLG1 gene and mtDNA depletion. Histological and enzymatic abnormalities in skeletal muscle support the diagnosis of this recently described mitochondrial disorder. This case is unique in that prenatal imaging suggested the diagnosis and that the confirmatory molecular diagnosis was established at 2 weeks of age. We describe prenatal MRI and neonatal laboratory disturbances that can point the clinician toward consideration of this diagnosis when treating infantile lactic acidosis.
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Current Protocols in Human Genetics - Real‐Time Quantitative PCR Analysis of Mitochondrial DNA Content
Current protocols in human genetics, 2011Co-Authors: Victor Venegas, Jing Wang, David Dimmock, Leejun C WongAbstract:Mitochondrial disorders are a group of complex and heterogeneous diseases that may be caused by molecular defects in the nuclear or mitochondrial genome. The biosynthesis and integrity of the small 16.6-kb mitochondrial genome require a group of nuclear encoded genes. The mitochondrial DNA (mtDNA) depletion syndromes (MDDSs) are autosomal recessive disorders caused by molecular defects in nuclear genes, and characterized by a reduction in mtDNA content. To date, mutations in at least nine genes (POLG, DGUOK, TK2, TYMP, MPV17, SUCLA2, SUCLG1, RRM2B, and C10orf2) have been reported to cause various forms of MDDSs. In the clinical setting, a simple method to determine mtDNA depletion would be useful prior to undertaking gene sequence analysis. This unit outlines the real-time quantitative polymerase chain reaction (qPCR) analysis of mtDNA content in tissues. MtDNA content varies among different tissues and at different ages in the same individual. Detailed protocols for the selection of nuclear genes for normalization, PCR set up, validation procedures, tissue and age matched controls, and sensitivity and specificity in various tissues, as well as interpretation of results are discussed. Curr. Protoc. Hum. Genet. 68:19.7.1-19.7.12 © 2011 by John Wiley & Sons, Inc. Keywords: mtDNA copy number; mtDNA content; mtDNA qPCR; quantification of mtDNA content; mtDNA depletion
Rosalba Carrozzo - One of the best experts on this subject based on the ideXlab platform.
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Succinate-CoA ligase deficiency due to mutations in SUCLA2 and SUCLG1: phenotype and genotype correlations in 71 patients
Journal of Inherited Metabolic Disease, 2016Co-Authors: Rosalba Carrozzo, Daniela Verrigni, Magnhild Rasmussen, Hernan Amartino, Marzia Bianchi, Daniela Buhas, Samir Mesli, Karin Naess, Alfred Peter Born, Berit WoldsethAbstract:Background The encephalomyopathic mtDNA depletion syndrome with methylmalonic aciduria is associated with deficiency of succinate-CoA ligase, caused by mutations in SUCLA2 or SUCLG1 . We report here 25 new patients with succinate-CoA ligase deficiency, and review the clinical and molecular findings in these and 46 previously reported patients. Patients and results Of the 71 patients, 50 had SUCLA2 mutations and 21 had SUCLG1 mutations. In the newly-reported 20 SUCLA2 patients we found 16 different mutations, of which nine were novel: two large gene deletions, a 1 bp duplication, two 1 bp deletions, a 3 bp insertion, a nonsense mutation and two missense mutations. In the newly-reported SUCLG1 patients, five missense mutations were identified, of which two were novel. The median onset of symptoms was two months for patients with SUCLA2 mutations and at birth for SUCLG1 patients. Median survival was 20 years for SUCLA2 and 20 months for SUCLG1 . Notable clinical differences between the two groups were hepatopathy, found in 38 % of SUCLG1 cases but not in SUCLA2 cases, and hypertrophic cardiomyopathy which was not reported in SUCLA2 patients, but documented in 14 % of cases with SUCLG1 mutations. Long survival, to age 20 years or older, was reported in 12 % of SUCLA2 and in 10 % of SUCLG1 patients. The most frequent abnormality on neuroimaging was basal ganglia involvement, found in 69 % of SUCLA2 and 80 % of SUCLG1 patients. Analysis of respiratory chain enzyme activities in muscle generally showed a combined deficiency of complexes I and IV, but normal histological and biochemical findings in muscle did not preclude a diagnosis of succinate-CoA ligase deficiency. In five patients, the urinary excretion of methylmalonic acid was only marginally elevated, whereas elevated plasma methylmalonic acid was consistently found. Conclusions To our knowledge, this is the largest study of patients with SUCLA2 and SUCLG1 deficiency. The most important findings were a significantly longer survival in patients with SUCLA2 mutations compared to SUCLG1 mutations and a trend towards longer survival in patients with missense mutations compared to loss-of-function mutations. Hypertrophic cardiomyopathy and liver involvement was exclusively found in patients with SUCLG1 mutations, whereas epilepsy was much more frequent in patients with SUCLA2 mutations compared to patients with SUCLG1 mutations. The mutation analysis revealed a number of novel mutations, including a homozygous deletion of the entire SUCLA2 gene, and we found evidence of two founder mutations in the Scandinavian population, in addition to the known SUCLA2 founder mutation in the Faroe Islands.
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succinate coa ligase deficiency due to mutations in sucla2 and SUCLG1 phenotype and genotype correlations in 71 patients
Journal of Inherited Metabolic Disease, 2016Co-Authors: Rosalba Carrozzo, Daniela Verrigni, Magnhild Rasmussen, Hernan Amartino, Marzia Bianchi, Daniela Buhas, Samir Mesli, Karin Naess, Alfred Peter Born, Berit WoldsethAbstract:Background The encephalomyopathic mtDNA depletion syndrome with methylmalonic aciduria is associated with deficiency of succinate-CoA ligase, caused by mutations in SUCLA2 or SUCLG1. We report here 25 new patients with succinate-CoA ligase deficiency, and review the clinical and molecular findings in these and 46 previously reported patients.
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Disorders of the Krebs Cycle
Physician's Guide to the Diagnosis Treatment and Follow-Up of Inherited Metabolic Diseases, 2014Co-Authors: Eva Morava, Rosalba CarrozzoAbstract:This chapter focuses on two classic Krebs cycle disorders (2-oxoglutaric aciduria and fumarase deficiency) and two recently discovered disorders of the Krebs cycle, severely affecting mitochondrial function and mitochondrial maintenance (succinyl-CoA synthetase –SCS – deficiencies, characterized by mutations in SUCLA2 and SUCLG1 genes). Fumarase deficiency and 2-oxoglutaric aciduria are rare disorders with global developmental delay and severe neurologic problems in infants. Patients with oxoglutaric aciduria have a variable severity of neurological involvement and metabolic acidosis and develop severe microcephaly and mental retardation. A special form (DOOR syndrome) occurs with sensorineural deafness and osteodystrophy. Patients with fumarase deficiency present with either a fulminant course associated with fatal outcome within the first 2 years of life or a subacute encephalopathy with profound speech delay without metabolic crises. SUCLA2 and SUCLG1 defects have the clinical presentation of mitochondrial depletion syndromes with profound hypotonia, progressive dystonia, and muscular atrophy, in addition to severe sensorineural hearing impairment, which has been specifically associated with SUCLA2 defect. The most important clues for the diagnosis in all these disorders rely in urine organic analysis. 2-oxoglutaric aciduria leads to chronic metabolic acidosis and variable urinary excretion of 2-oxoglutarate, while fumarase deficiency occurs with an increased excretion of fumarate associated with succinate and lactate excretion with eventual 2-oxoglutaric aciduria. A normal excretion of fumaric acid and a relative high fumarase residual activity do not rule out fumarase deficiency. In questionable cases mutation analysis is needed to confirm the diagnosis. In SCS defects mild methylmalonic aciduria with abnormal urine carnitine-ester profile is associated with only subtle abnormalities of the Krebs cycle intermediates. Due to the recognizable pattern of dystonia/±deafness syndrome and mild methylmalonic aciduria in SCS defects, direct genetic testing is a possible approach in the diagnosis of SUCLA2 and SUCLG1 defects. Carrier screening in fumarase deficiency is important due to the possible increased risk for certain malignancies.
Elsebet Ostergaard - One of the best experts on this subject based on the ideXlab platform.
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Two transgenic mouse models for beta subunit components of succinate-CoA ligase yielding pleiotropic metabolic alterations.
Biochemical Journal, 2016Co-Authors: Gergely Kacso, Judit Doczi, Dora Ravasz, Beáta Németh, Ory Madgar, Ann Saada, Polina Ilin, Chaya Miller, Elsebet Ostergaard, Iordan IordanovAbstract:Succinate-CoA ligase (SUCL) is a heterodimer enzyme composed of SUCLG1 α-subunit and a substrate-specific Sucla2 or Suclg2 β-subunit yielding ATP or GTP, respectively. In humans, the deficiency of this enzyme leads to encephalomyopathy with or without methylmalonyl aciduria, in addition to resulting in mitochondrial DNA depletion. We generated mice lacking either one Sucla2 or Suclg2 allele. Sucla2 heterozygote mice exhibited tissue- and age-dependent decreases in Sucla2 expression associated with decreases in ATP-forming activity, but rebound increases in cardiac Suclg2 expression and GTP-forming activity. Bioenergetic parameters including substrate-level phosphorylation (SLP) were not different between wild-type and Sucla2 heterozygote mice unless a submaximal pharmacological inhibition of SUCL was concomitantly present. mtDNA contents were moderately decreased, but blood carnitine esters were significantly elevated. Suclg2 heterozygote mice exhibited decreases in Suclg2 expression but no rebound increases in Sucla2 expression or changes in bioenergetic parameters. Surprisingly, deletion of one Suclg2 allele in Sucla2 heterozygote mice still led to a rebound but protracted increase in Suclg2 expression, yielding double heterozygote mice with no alterations in GTP-forming activity or SLP, but more pronounced changes in mtDNA content and blood carnitine esters, and an increase in succinate dehydrogenase activity. We conclude that a partial reduction in Sucla2 elicits rebound increases in Suclg2 expression, which is sufficiently dominant to overcome even a concomitant deletion of one Suclg2 allele, pleiotropically affecting metabolic pathways associated with SUCL. These results as well as the availability of the transgenic mouse colonies will be of value in understanding SUCL deficiency.
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Exclusive neuronal expression of SUCLA2 in the human brain
Brain Structure and Function, 2015Co-Authors: Arpád Dobolyi, Elsebet Ostergaard, Attila G. Bagó, Mária J. Molnár, Miklós Palkovits, Vera Adam-vizi, Tamás Dóczi, Christos ChinopoulosAbstract:SUCLA2 encodes the ATP-forming β subunit (A-SUCL-β) of succinyl-CoA ligase, an enzyme of the citric acid cycle. Mutations in SUCLA2 lead to a mitochondrial disorder manifesting as encephalomyopathy with dystonia, deafness and lesions in the basal ganglia. Despite the distinct brain pathology associated with SUCLA2 mutations, the precise localization of SUCLA2 protein has never been investigated. Here, we show that immunoreactivity of A-SUCL-β in surgical human cortical tissue samples was present exclusively in neurons, identified by their morphology and visualized by double labeling with a fluorescent Nissl dye. A-SUCL-β immunoreactivity co-localized >99 % with that of the d subunit of the mitochondrial F_0–F_1 ATP synthase. Specificity of the anti-A-SUCL-β antiserum was verified by the absence of labeling in fibroblasts from a patient with a complete deletion of SUCLA2 . A-SUCL-β immunoreactivity was absent in glial cells, identified by antibodies directed against the glial markers GFAP and S100. Furthermore, in situ hybridization histochemistry demonstrated that SUCLA2 mRNA was present in Nissl-labeled neurons but not glial cells labeled with S100. Immunoreactivity of the GTP-forming β subunit (G-SUCL-β) encoded by SUCLG2 , or in situ hybridization histochemistry for SUCLG2 mRNA could not be demonstrated in either neurons or astrocytes. Western blotting of post mortem brain samples revealed minor G-SUCL-β immunoreactivity that was, however, not upregulated in samples obtained from diabetic versus non-diabetic patients, as has been described for murine brain. Our work establishes that SUCLA2 is expressed exclusively in neurons in the human cerebral cortex.
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the severity of phenotype linked to SUCLG1 mutations could be correlated with residual amount of SUCLG1 protein
Journal of Medical Genetics, 2010Co-Authors: Cecile Rouzier, Le S Guedardmereuze, Konstantina Fragaki, Valerie Serre, J Miro, Sylvie Tufferygiraud, Annabelle Chaussenot, Sylvie Bannwarth, C Caruba, Elsebet OstergaardAbstract:Background Succinate-CoA ligase deficiency is responsible for encephalomyopathy with mitochondrial DNA depletion and mild methylmalonic aciduria. Mutations in SUCLA2 , the gene encoding a β subunit of succinate-CoA ligase, have been reported in 17 patients until now. Mutations in SUCLG1 , encoding the α subunit of the enzyme, have been described in two pedigrees only. Methods and findings In this study, two unrelated patients harbouring three novel pathogenic mutations in SUCLG1 were reported. The first patient had a severe disease at birth. He was compound heterozygous for a missense mutation (p.Pro170Arg) and a c.97+3G>C mutation, which leads to the complete skipping of exon 1 in a minigene expression system. The involvement of SUCLG1 was confirmed by western blot analysis, which showed absence of SUCLG1 protein in fibroblasts. The second patient has a milder phenotype, similar to that of patients with SUCLA2 mutations, and is still alive at 12 years of age. Western blot analysis showed some residual SUCLG1 protein in patient9s fibroblasts. Conclusions Our results suggest that SUCLG1 mutations that lead to complete absence of SUCLG1 protein are responsible for a very severe disorder with antenatal manifestations, whereas a SUCLA2 -like phenotype is found in patients with residual SUCLG1 protein. Furthermore, it is shown that in the absence of SUCLG1 protein, no SUCLA2 protein is found in fibroblasts by western blot analysis. This result is consistent with a degradation of SUCLA2 when its heterodimer partner, SUCLG1, is absent.
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a novel missense mutation in SUCLG1 associated with mitochondrial dna depletion encephalomyopathic form with methylmalonic aciduria
European Journal of Pediatrics, 2010Co-Authors: Elsebet Ostergaard, Marianne Schwartz, Mustafa Batbayli, E Christensen, Ola Hjalmarson, Gittan Kollberg, Elisabeth HolmeAbstract:Mitochondrial DNA depletion, encephalomyopathic form, with methylmalonic aciduria is associated with mutations in SUCLA2, the gene encoding a β subunit of succinate-CoA ligase, where 17 patients have been reported. Mutations in SUCLG1, encoding the α subunit of the enzyme, have been reported in only one family, where a homozygous 2 bp deletion was associated with fatal infantile lactic acidosis. We here report a patient with a novel homozygous missense mutation in SUCLG1, whose phenotype is similar to that of patients with SUCLA2 mutations.
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Deficiency of the α Subunit of Succinate–Coenzyme A Ligase Causes Fatal Infantile Lactic Acidosis with Mitochondrial DNA Depletion
American Journal of Human Genetics, 2007Co-Authors: Elsebet Ostergaard, Ernst Christensen, Elisabeth Kristensen, Bodil Mogensen, Morten Duno, Eric A. Shoubridge, Flemming WibrandAbstract:Fatal infantile lactic acidosis is a severe metabolic disorder characterized by the onset of lactic acidosis within the 1st d of life and early death. We found a combined respiratory-chain enzyme deficiency associated with mitochondrial DNA (mtDNA) depletion in a small consanguineous family with this disorder. To identify the disease-causing gene, we performed single-nucleotide polymorphism homozygosity mapping and found homozygous regions on four chromosomes. DNA sequencing revealed a homozygous 2-bp deletion in SUCLG1, a gene that encodes the α subunit of the Krebs-cycle enzyme succinate–coenzyme A ligase (SUCL). The mtDNA depletion is likely explained by decreased mitochondrial nucleoside diphosphate kinase (NDPK) activity resulting from the inability of NDPK to form a complex with SUCL.
Christos Chinopoulos - One of the best experts on this subject based on the ideXlab platform.
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mutated SUCLG1 causes mislocalization of suclg2 protein morphological alterations of mitochondria and an early onset severe neurometabolic disorder
Molecular Genetics and Metabolism, 2019Co-Authors: Christos Chinopoulos, Spyros Batzios, Lambertus P Van Den Heuvel, Richard J Rodenburg, R J H Smeets, Hans R Waterham, Marjolein Turkenburg, Jos P N Ruiter, Ronald J A Wanders, Judit DocziAbstract:Abstract Succinate-CoA ligase (SUCL) is a heterodimer consisting of an alpha subunit encoded by SUCLG1, and a beta subunit encoded by either SUCLA2 or SUCLG2 catalyzing an ATP- or GTP-forming reaction, respectively, in the mitochondrial matrix. The deficiency of this enzyme represents an encephalomyopathic form of mtDNA depletion syndromes. We describe the fatal clinical course of a female patient with a pathogenic mutation in SUCLG1 (c.626C > A, p.Ala209Glu) heterozygous at the genomic DNA level, but homozygous at the transcriptional level. The patient exhibited early-onset neurometabolic abnormality culminating in severe brain atrophy and dystonia leading to death by the age of 3.5 years. Urine and plasma metabolite profiling was consistent with SUCL deficiency which was confirmed by enzyme analysis and lack of mitochondrial substrate-level phosphorylation (mSLP) in skin fibroblasts. Oxygen consumption- but not extracellular acidification rates were altered only when using glutamine as a substrate, and this was associated with mild mtDNA depletion and no changes in ETC activities. Immunoblot analysis revealed no detectable levels of SUCLG1, while SUCLA2 and SUCLG2 protein expressions were largely reduced. Confocal imaging of triple immunocytochemistry of skin fibroblasts showed that SUCLG2 co-localized only partially with the mitochondrial network which otherwise exhibited an increase in fragmentation compared to control cells. Our results outline the catastrophic consequences of the mutated SUCLG1 leading to strongly reduced SUCL activity, mSLP impairment, mislocalization of SUCLG2, morphological alterations in mitochondria and clinically to a severe neurometabolic disease, but in the absence of changes in mtDNA levels or respiratory complex activities.
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Localization of SUCLA2 and SUCLG2 subunits of succinyl CoA ligase within the cerebral cortex suggests the absence of matrix substrate-level phosphorylation in glial cells of the human brain
Journal of Bioenergetics and Biomembranes, 2015Co-Authors: Arpád Dobolyi, Attila G. Bagó, Mária J. Molnár, Miklós Palkovits, Vera Adam-vizi, Christos ChinopoulosAbstract:We have recently shown that the ATP-forming SUCLA2 subunit of succinyl-CoA ligase, an enzyme of the citric acid cycle, is exclusively expressed in neurons of the human cerebral cortex; GFAP- and S100-positive astroglial cells did not exhibit immunohistoreactivity or in situ hybridization reactivity for either SUCLA2 or the GTP-forming SUCLG2. However, Western blotting of post mortem samples revealed a minor SUCLG2 immunoreactivity. In the present work we sought to identify the cell type(s) harboring SUCLG2 in paraformaldehyde-fixed, free-floating surgical human cortical tissue samples. Specificity of SUCLG2 antiserum was supported by co-localization with mitotracker orange staining of paraformaldehyde-fixed human fibroblast cultures, delineating the mitochondrial network. In human cortical tissue samples, microglia and oligodendroglia were identified by antibodies directed against Iba1 and myelin basic protein, respectively. Double immunofluorescence for SUCLG2 and Iba1 or myelin basic protein exhibited no co-staining; instead, SUCLG2 appeared to outline the cerebral microvasculature. In accordance to our previous work there was no co-localization of SUCLA2 immunoreactivity with either Iba1 or myelin basic protein. We conclude that SUCLG2 exist only in cells forming the vasculature or its contents in the human brain. The absence of SUCLA2 and SUCLG2 in human glia is in compliance with the presence of alternative pathways occurring in these cells, namely the GABA shunt and ketone body metabolism which do not require succinyl CoA ligase activity, and glutamate dehydrogenase 1, an enzyme exhibiting exquisite sensitivity to inhibition by GTP.
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Exclusive neuronal expression of SUCLA2 in the human brain
Brain Structure and Function, 2015Co-Authors: Arpád Dobolyi, Elsebet Ostergaard, Attila G. Bagó, Mária J. Molnár, Miklós Palkovits, Vera Adam-vizi, Tamás Dóczi, Christos ChinopoulosAbstract:SUCLA2 encodes the ATP-forming β subunit (A-SUCL-β) of succinyl-CoA ligase, an enzyme of the citric acid cycle. Mutations in SUCLA2 lead to a mitochondrial disorder manifesting as encephalomyopathy with dystonia, deafness and lesions in the basal ganglia. Despite the distinct brain pathology associated with SUCLA2 mutations, the precise localization of SUCLA2 protein has never been investigated. Here, we show that immunoreactivity of A-SUCL-β in surgical human cortical tissue samples was present exclusively in neurons, identified by their morphology and visualized by double labeling with a fluorescent Nissl dye. A-SUCL-β immunoreactivity co-localized >99 % with that of the d subunit of the mitochondrial F_0–F_1 ATP synthase. Specificity of the anti-A-SUCL-β antiserum was verified by the absence of labeling in fibroblasts from a patient with a complete deletion of SUCLA2 . A-SUCL-β immunoreactivity was absent in glial cells, identified by antibodies directed against the glial markers GFAP and S100. Furthermore, in situ hybridization histochemistry demonstrated that SUCLA2 mRNA was present in Nissl-labeled neurons but not glial cells labeled with S100. Immunoreactivity of the GTP-forming β subunit (G-SUCL-β) encoded by SUCLG2 , or in situ hybridization histochemistry for SUCLG2 mRNA could not be demonstrated in either neurons or astrocytes. Western blotting of post mortem brain samples revealed minor G-SUCL-β immunoreactivity that was, however, not upregulated in samples obtained from diabetic versus non-diabetic patients, as has been described for murine brain. Our work establishes that SUCLA2 is expressed exclusively in neurons in the human cerebral cortex.
