1
|
Gougeard N, Sancho-Vaello E, Fernández-Murga ML, Martínez-Sinisterra B, Loukili-Hassani B, Häberle J, Marco-Marín C, Rubio V. Use of pure recombinant human enzymes to assess the disease-causing potential of missense mutations in urea cycle disorders, applied to N-acetylglutamate synthase deficiency. J Inherit Metab Dis 2024. [PMID: 38740568 DOI: 10.1002/jimd.12747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Revised: 04/21/2024] [Accepted: 04/23/2024] [Indexed: 05/16/2024]
Abstract
N-acetylglutamate synthase (NAGS) makes acetylglutamate, the essential activator of the first, regulatory enzyme of the urea cycle, carbamoyl phosphate synthetase 1 (CPS1). NAGS deficiency (NAGSD) and CPS1 deficiency (CPS1D) present identical phenotypes. However, they must be distinguished, because NAGSD is cured by substitutive therapy with the N-acetyl-L-glutamate analogue N-carbamyl-L-glutamate, while curative therapy of CPS1D requires liver transplantation. Since their differentiation is done genetically, it is important to ascertain the disease-causing potential of CPS1 and NAGS genetic variants. With this goal, we previously carried out site-directed mutagenesis studies with pure recombinant human CPS1. We could not do the same with human NAGS (HuNAGS) because of enzyme instability, leading to our prior utilization of a bacterial NAGS as an imperfect surrogate of HuNAGS. We now use genuine HuNAGS, stabilized as a chimera of its conserved domain (cHuNAGS) with the maltose binding protein (MBP), and produced in Escherichia coli. MBP-cHuNAGS linker cleavage allowed assessment of the enzymatic properties and thermal stability of cHuNAGS, either wild-type or hosting each one of 23 nonsynonymous single-base changes found in NAGSD patients. For all but one change, disease causation was accounted by the enzymatic alterations identified, including, depending on the variant, loss of arginine activation, increased Km Glutamate, active site inactivation, decreased thermal stability, and protein misfolding. Our present approach outperforms experimental in vitro use of bacterial NAGS or in silico utilization of prediction servers (including AlphaMissense), illustrating with HuNAGS the value for UCDs of using recombinant enzymes for assessing disease-causation and molecular pathogenesis, and for therapeutic guidance.
Collapse
Affiliation(s)
- Nadine Gougeard
- Instituto de Biomedicina de Valencia, IBV-CSIC, Valencia, Spain
- Group 739, Centro de Investigación Biomédica en Red de Enfermedades Raras, (CIBERER-ISCIII) at the IBV-CSIC, Valencia, Spain
| | | | | | | | | | - Johannes Häberle
- University Children's Hospital Zurich and Children's Research Centre, Zurich, Switzerland
| | - Clara Marco-Marín
- Instituto de Biomedicina de Valencia, IBV-CSIC, Valencia, Spain
- Group 739, Centro de Investigación Biomédica en Red de Enfermedades Raras, (CIBERER-ISCIII) at the IBV-CSIC, Valencia, Spain
| | - Vicente Rubio
- Instituto de Biomedicina de Valencia, IBV-CSIC, Valencia, Spain
- Group 739, Centro de Investigación Biomédica en Red de Enfermedades Raras, (CIBERER-ISCIII) at the IBV-CSIC, Valencia, Spain
| |
Collapse
|
2
|
Caldovic L, Ahn JJ, Andricovic J, Balick VM, Brayer M, Chansky PA, Dawson T, Edwards AC, Felsen SE, Ismat K, Jagannathan SV, Mann BT, Medina JA, Morizono T, Morizono M, Salameh S, Vashist N, Williams EC, Zhou Z, Morizono H. Datamining approaches for examining the low prevalence of N-acetylglutamate synthase deficiency and understanding transcriptional regulation of urea cycle genes. J Inherit Metab Dis 2023. [PMID: 37847851 DOI: 10.1002/jimd.12687] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Revised: 10/09/2023] [Accepted: 10/10/2023] [Indexed: 10/19/2023]
Abstract
Ammonia, which is toxic to the brain, is converted into non-toxic urea, through a pathway of six enzymatically catalyzed steps known as the urea cycle. In this pathway, N-acetylglutamate synthase (NAGS, EC 2.3.1.1) catalyzes the formation of N-acetylglutamate (NAG) from glutamate and acetyl coenzyme A. NAGS deficiency (NAGSD) is the rarest of the urea cycle disorders, yet is unique in that ureagenesis can be restored with the drug N-carbamylglutamate (NCG). We investigated whether the rarity of NAGSD could be due to low sequence variation in the NAGS genomic region, high NAGS tolerance for amino acid replacements, and alternative sources of NAG and NCG in the body. We also evaluated whether the small genomic footprint of the NAGS catalytic domain might play a role. The small number of patients diagnosed with NAGSD could result from the absence of specific disease biomarkers and/or short NAGS catalytic domain. We screened for sequence variants in NAGS regulatory regions in patients suspected of having NAGSD and found a novel NAGS regulatory element in the first intron of the NAGS gene. We applied the same datamining approach to identify regulatory elements in the remaining urea cycle genes. In addition to the known promoters and enhancers of each gene, we identified several novel regulatory elements in their upstream regions and first introns. The identification of cis-regulatory elements of urea cycle genes and their associated transcription factors holds promise for uncovering shared mechanisms governing urea cycle gene expression and potentially leading to new treatments for urea cycle disorders.
Collapse
Affiliation(s)
- Ljubica Caldovic
- Center for Genetic Medicine Research, Children's National Research Institute, Children's National Hospital, Washington, DC, USA
- Department of Genomics and Precision Medicine, School of Medicine and Health Sciences, The George Washington University, Washington, DC, USA
| | - Julie J Ahn
- Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, DC, USA
| | - Jacklyn Andricovic
- Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, DC, USA
| | - Veronica M Balick
- Department of Biochemistry and Molecular Medicine, The George Washington University School of Medicine and Health Sciences, Washington, DC, USA
| | - Mallory Brayer
- Department of Biological Sciences, The George Washington University, Washington, DC, USA
| | - Pamela A Chansky
- The Institute for Biomedical Science, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
| | - Tyson Dawson
- The Institute for Biomedical Science, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
- AMPEL BioSolutions LLC, Charlottesville, Virginia, USA
| | - Alex C Edwards
- The Institute for Biomedical Science, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
- Center for Neuroscience Research, Children's National Research Institute, Children's National Hospital, Washington, DC, USA
| | - Sara E Felsen
- The Institute for Biomedical Science, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
- Center for Neuroscience Research, Children's National Research Institute, Children's National Hospital, Washington, DC, USA
| | - Karim Ismat
- Center for Genetic Medicine Research, Children's National Research Institute, Children's National Hospital, Washington, DC, USA
- Department of Genomics and Precision Medicine, School of Medicine and Health Sciences, The George Washington University, Washington, DC, USA
| | - Sveta V Jagannathan
- The Institute for Biomedical Science, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
| | - Brendan T Mann
- Department of Microbiology, Immunology, and Tropical Medicine, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
| | - Jacob A Medina
- The Institute for Biomedical Science, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
| | - Toshio Morizono
- College of Science and Engineering, University of Minnesota, Minneapolis, Minnesota, USA
| | - Michio Morizono
- College of Science and Engineering, University of Minnesota, Minneapolis, Minnesota, USA
| | - Shatha Salameh
- Department of Pharmacology & Physiology, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
- Sheikh Zayed Institute for Pediatric Surgical Innovation, Children's National Hospital, Washington, DC, USA
| | - Neerja Vashist
- Center for Genetic Medicine Research, Children's National Research Institute, Children's National Hospital, Washington, DC, USA
- Department of Genomics and Precision Medicine, School of Medicine and Health Sciences, The George Washington University, Washington, DC, USA
| | - Emily C Williams
- Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, DC, USA
- The George Washington University Cancer Center, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
| | - Zhe Zhou
- Department of Civil and Environmental Engineering, The George Washington University, Washington, DC, USA
| | - Hiroki Morizono
- Center for Genetic Medicine Research, Children's National Research Institute, Children's National Hospital, Washington, DC, USA
- Department of Genomics and Precision Medicine, School of Medicine and Health Sciences, The George Washington University, Washington, DC, USA
| |
Collapse
|
3
|
Selvanathan A, Demetriou K, Lynch M, Lipke M, Bursle C, Elliott A, Inwood A, Foyn L, McWhinney B, Coman D, McGill J. N-acetylglutamate synthase deficiency with associated 3-methylglutaconic aciduria: A case report. JIMD Rep 2022; 63:420-424. [PMID: 36101823 PMCID: PMC9458610 DOI: 10.1002/jmd2.12318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/07/2022] [Revised: 07/01/2022] [Accepted: 07/12/2022] [Indexed: 11/05/2022] Open
Abstract
N-acetylglutamate synthase (NAGS) deficiency is a rare autosomal recessive disorder, which results in the inability to activate the key urea cycle enzyme, carbamoylphosphate synthetase 1 (CPS1). Patients often suffer life-threatening episodes of hyperammonaemia, both in the neonatal period and also at subsequent times of catabolic stress. Because NAGS generates the cofactor for CPS1, these two disorders are difficult to distinguish biochemically. However, there have now been numerous case reports of 3-methylglutaconic aciduria (3-MGA), a marker seen in mitochondrial disorders, occurring in CPS1 deficiency. Previously, this had not been reported in NAGS deficiency. We report a four-day-old neonate who was noted to have 3-MGA at the time of significant hyperammonaemia and lactic acidosis. Low plasma citrulline and borderline orotic aciduria were additional findings that suggested a proximal urea cycle disorder. Subsequent molecular testing identified bi-allelic pathogenic variants in NAGS. The 3-MGA was present at the time of persistent lactic acidosis, but improved with normalization of serum lactate, suggesting that it may reflect secondary mitochondrial dysfunction. NAGS deficiency should therefore also be considered in patients with hyperammonaemia and 3-MGA. Studies in larger numbers of patients are required to determine whether it could be a biomarker for severe decompensations.
Collapse
Affiliation(s)
- Arthavan Selvanathan
- Queensland Lifespan Metabolic Medicine ServiceQueensland Children's HospitalBrisbaneAustralia
| | - Kalliope Demetriou
- Queensland Lifespan Metabolic Medicine ServiceQueensland Children's HospitalBrisbaneAustralia
| | - Matthew Lynch
- Queensland Lifespan Metabolic Medicine ServiceQueensland Children's HospitalBrisbaneAustralia
| | - Michelle Lipke
- Queensland Lifespan Metabolic Medicine ServiceQueensland Children's HospitalBrisbaneAustralia
| | - Carolyn Bursle
- Queensland Lifespan Metabolic Medicine ServiceQueensland Children's HospitalBrisbaneAustralia
| | - Aoife Elliott
- Queensland Lifespan Metabolic Medicine ServiceQueensland Children's HospitalBrisbaneAustralia
| | - Anita Inwood
- Queensland Lifespan Metabolic Medicine ServiceQueensland Children's HospitalBrisbaneAustralia
| | - Leanne Foyn
- Chemical Pathology, Central LaboratoryPathology QueenslandHerstonAustralia
| | - Brett McWhinney
- Chemical Pathology, Central LaboratoryPathology QueenslandHerstonAustralia
| | - David Coman
- Queensland Lifespan Metabolic Medicine ServiceQueensland Children's HospitalBrisbaneAustralia
- School of MedicineUniversity of QueenslandBrisbaneAustralia
| | - Jim McGill
- Chemical Pathology, Central LaboratoryPathology QueenslandHerstonAustralia
| |
Collapse
|
4
|
Gene delivery corrects N-acetylglutamate synthase deficiency and enables insights in the physiological impact of L-arginine activation of N-acetylglutamate synthase. Sci Rep 2021; 11:3580. [PMID: 33574402 PMCID: PMC7878489 DOI: 10.1038/s41598-021-82994-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Accepted: 01/20/2021] [Indexed: 11/19/2022] Open
Abstract
The urea cycle protects the central nervous system from ammonia toxicity by converting ammonia to urea. N-acetylglutamate synthase (NAGS) catalyzes formation of N-acetylglutamate, an essential allosteric activator of carbamylphosphate synthetase 1. Enzymatic activity of mammalian NAGS doubles in the presence of L-arginine, but the physiological significance of NAGS activation by L-arginine has been unknown. The NAGS knockout (Nags−/−) mouse is an animal model of inducible hyperammonemia, which develops hyperammonemia without N-carbamylglutamate and L-citrulline supplementation (NCG + Cit). We used adeno associated virus (AAV) based gene transfer to correct NAGS deficiency in the Nags−/− mice, established the dose of the vector needed to rescue Nags−/− mice from hyperammonemia and measured expression levels of Nags mRNA and NAGS protein in the livers of rescued animals. This methodology was used to investigate the effect of L-arginine on ureagenesis in vivo by treating Nags−/− mice with AAV vectors encoding either wild-type or E354A mutant mouse NAGS (mNAGS), which is not activated by L-arginine. The Nags−/− mice expressing E354A mNAGS were viable but had elevated plasma ammonia concentration despite similar levels of the E354A and wild-type mNAGS proteins. The corresponding mutation in human NAGS (NP_694551.1:p.E360D) that abolishes binding and activation by L-arginine was identified in a patient with NAGS deficiency. Our results show that NAGS deficiency can be rescued by gene therapy, and suggest that L-arginine binding to the NAGS enzyme is essential for normal ureagenesis.
Collapse
|
5
|
Makris G, Lauber M, Rüfenacht V, Gemperle C, Diez-Fernandez C, Caldovic L, Froese DS, Häberle J. Clinical and structural insights into potential dominant negative triggers of proximal urea cycle disorders. Biochimie 2020; 183:89-99. [PMID: 33309754 DOI: 10.1016/j.biochi.2020.12.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 12/04/2020] [Accepted: 12/08/2020] [Indexed: 12/31/2022]
Abstract
Despite biochemical and genetic testing being the golden standards for identification of proximal urea cycle disorders (UCDs), genotype-phenotype correlations are often unclear. Co-occurring partial defects affecting more than one gene have not been demonstrated so far in proximal UCDs. Here, we analyzed the mutational spectrum of 557 suspected proximal UCD individuals. We probed oligomerizing forms of NAGS, CPS1 and OTC, and evaluated the surface exposure of residues mutated in heterozygously affected individuals. BN-PAGE and gel-filtration chromatography were employed to discover protein-protein interactions within recombinant enzymes. From a total of 281 confirmed patients, only 15 were identified as "heterozygous-only" candidates (i.e. single defective allele). Within these cases, the only missense variants to potentially qualify as dominant negative triggers were CPS1 p.Gly401Arg and NAGS p.Thr181Ala and p.Tyr512Cys, as assessed by residue oligomerization capacity and surface exposure. However, all three candidates seem to participate in critical intramolecular functions, thus, unlikely to facilitate protein-protein interactions. This interpretation is further supported by BN-PAGE and gel-filtration analyses revealing no multiprotein proximal urea cycle complex formation. Collectively, genetic analysis, structural considerations and in vitro experiments point against a prominent role of dominant negative effects in human proximal UCDs.
Collapse
Affiliation(s)
- Georgios Makris
- Division of Metabolism and Children's Research Center, University Children's Hospital Zurich, Zurich, Switzerland
| | - Matthias Lauber
- Division of Metabolism and Children's Research Center, University Children's Hospital Zurich, Zurich, Switzerland
| | - Véronique Rüfenacht
- Division of Metabolism and Children's Research Center, University Children's Hospital Zurich, Zurich, Switzerland
| | - Corinne Gemperle
- Division of Metabolism and Children's Research Center, University Children's Hospital Zurich, Zurich, Switzerland
| | - Carmen Diez-Fernandez
- Division of Metabolism and Children's Research Center, University Children's Hospital Zurich, Zurich, Switzerland; Nextech Invest, Bahnhofstrasse 18, 8001, Zurich, Switzerland
| | - Ljubica Caldovic
- Center for Genetic Medicine Research, Children's National Hospital, Washington, DC, USA
| | - D Sean Froese
- Division of Metabolism and Children's Research Center, University Children's Hospital Zurich, Zurich, Switzerland
| | - Johannes Häberle
- Division of Metabolism and Children's Research Center, University Children's Hospital Zurich, Zurich, Switzerland.
| |
Collapse
|
6
|
Kenneson A, Singh RH. Presentation and management of N-acetylglutamate synthase deficiency: a review of the literature. Orphanet J Rare Dis 2020; 15:279. [PMID: 33036647 PMCID: PMC7545900 DOI: 10.1186/s13023-020-01560-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Accepted: 09/24/2020] [Indexed: 12/19/2022] Open
Abstract
Background N-Acetylglutamate synthase (NAGS) deficiency is an extremely rare autosomal recessive metabolic disorder affecting the urea cycle, leading to episodes of hyperammonemia which can cause significant morbidity and mortality. Since its recognition in 1981, NAGS deficiency has been treated with carbamylglutamate with or without other measures (nutritional, ammonia scavengers, dialytic, etc.). We conducted a systematic literature review of NAGS deficiency to summarize current knowledge around presentation and management. Methods Case reports and case series were identified using the Medline database, as well as references from other articles and a general internet search. Clinical data related to presentation and management were abstracted by two reviewers. Results In total, 98 cases of NAGS deficiency from 79 families, in 48 articles or abstracts were identified. Of these, 1 was diagnosed prenatally, 57 were neonatal cases, 34 were post-neonatal, and 6 did not specify age at presentation or were asymptomatic at diagnosis. Twenty-one cases had relevant family history. We summarize triggers of hyperammonemic episodes, diagnosis, clinical signs and symptoms, and management strategies. DNA testing is the preferred method of diagnosis, although therapeutic trials to assess response of ammonia levels to carbamylglutamate may also be helpful. Management usually consists of treatment with carbamylglutamate, although the reported maintenance dose varied across case reports. Protein restriction was sometimes used in conjunction with carbamylglutamate. Supplementation with citrulline, arginine, and sodium benzoate also were reported. Conclusions Presentation of NAGS deficiency varies by age and symptoms. In addition, both diagnosis and management have evolved over time and vary across clinics. Prompt recognition and appropriate treatment of NAGS deficiency with carbamylglutamate may improve outcomes of affected individuals. Further research is needed to assess the roles of protein restriction and supplements in the treatment of NAGS deficiency, especially during times of illness or lack of access to carbamylglutamate.
Collapse
Affiliation(s)
- Aileen Kenneson
- Department of Human Genetics, Emory University, Atlanta, GA, USA.
| | - Rani H Singh
- Department of Human Genetics, Emory University, Atlanta, GA, USA. .,Department of Pediatrics, Emory University, Atlanta, GA, USA.
| |
Collapse
|
7
|
Heibel SK, McGuire PJ, Haskins N, Datta Majumdar H, Rayavarapu S, Nagaraju K, Hathout Y, Brown K, Tuchman M, Caldovic L. AMP-activated protein kinase signaling regulated expression of urea cycle enzymes in response to changes in dietary protein intake. J Inherit Metab Dis 2019; 42:1088-1096. [PMID: 31177541 PMCID: PMC7385982 DOI: 10.1002/jimd.12133] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 04/02/2019] [Accepted: 06/05/2019] [Indexed: 12/30/2022]
Abstract
Abundance of urea cycle enzymes in the liver is regulated by dietary protein intake. Although urea cycle enzyme levels rise in response to a high-protein (HP) diet, signaling networks that sense dietary protein intake and trigger changes in expression of urea cycle genes have not been identified. The aim of this study was to identify signaling pathway(s) that respond to changes in protein intake and regulate expression of urea cycle genes in mice and human hepatocytes. Mice were adapted to either HP or low-protein diets followed by isolation of liver protein and mRNA and integrated analysis of the proteomic and transcriptomic data. HP diet led to increased expression of mRNA and enzymes in amino acid degradation pathways and decreased expression of mRNA and enzymes in carbohydrate and fat metabolism, which implicated adenosine monophosphate-activated protein kinase (AMPK) as a possible regulator. Primary human hepatocytes, treated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) an activator of AMPK, were used to test whether AMPK regulates expression of urea cycle genes. The abundance of carbamoylphosphate synthetase 1 and ornithine transcarbamylase mRNA increased in hepatocytes treated with AICAR, which supports a role for AMPK signaling in regulation of the urea cycle. Because AMPK is either a target of drugs used to treat type-2 diabetes, these drugs might increase the expression of urea cycle enzymes in patients with partial urea cycle disorders, which could be the basis of a new therapeutic approach.
Collapse
Affiliation(s)
- Sandra Kirsch Heibel
- Center for Genetic Medicine Research, Children’s National Medical Center, 111 Michigan Ave NW, Washington DC, USA
| | | | - Nantaporn Haskins
- Center for Genetic Medicine Research, Children’s National Medical Center, 111 Michigan Ave NW, Washington DC, USA
| | - Himani Datta Majumdar
- Center for Genetic Medicine Research, Children’s National Medical Center, 111 Michigan Ave NW, Washington DC, USA
| | - Sree Rayavarapu
- Center for Genetic Medicine Research, Children’s National Medical Center, 111 Michigan Ave NW, Washington DC, USA
| | - Kanneboyina Nagaraju
- Department of Pharmaceutical Sciences, Binghamton University, Binghamton NY, USA
| | - Yetrib Hathout
- Department of Pharmaceutical Sciences, Binghamton University, Binghamton NY, USA
| | - Kristy Brown
- Center for Genetic Medicine Research, Children’s National Medical Center, 111 Michigan Ave NW, Washington DC, USA
| | - Mendel Tuchman
- Center for Genetic Medicine Research, Children’s National Medical Center, 111 Michigan Ave NW, Washington DC, USA
| | - Ljubica Caldovic
- Center for Genetic Medicine Research, Children’s National Medical Center, 111 Michigan Ave NW, Washington DC, USA
| |
Collapse
|
8
|
Häberle J, Burlina A, Chakrapani A, Dixon M, Karall D, Lindner M, Mandel H, Martinelli D, Pintos-Morell G, Santer R, Skouma A, Servais A, Tal G, Rubio V, Huemer M, Dionisi-Vici C. Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision. J Inherit Metab Dis 2019; 42:1192-1230. [PMID: 30982989 DOI: 10.1002/jimd.12100] [Citation(s) in RCA: 249] [Impact Index Per Article: 49.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 04/04/2019] [Accepted: 04/08/2019] [Indexed: 02/06/2023]
Abstract
In 2012, we published guidelines summarizing and evaluating late 2011 evidence for diagnosis and therapy of urea cycle disorders (UCDs). With 1:35 000 estimated incidence, UCDs cause hyperammonemia of neonatal (~50%) or late onset that can lead to intellectual disability or death, even while effective therapies do exist. In the 7 years that have elapsed since the first guideline was published, abundant novel information has accumulated, experience on newborn screening for some UCDs has widened, a novel hyperammonemia-causing genetic disorder has been reported, glycerol phenylbutyrate has been introduced as a treatment, and novel promising therapeutic avenues (including gene therapy) have been opened. Several factors including the impact of the first edition of these guidelines (frequently read and quoted) may have increased awareness among health professionals and patient families. However, under-recognition and delayed diagnosis of UCDs still appear widespread. It was therefore necessary to revise the original guidelines to ensure an up-to-date frame of reference for professionals and patients as well as for awareness campaigns. This was accomplished by keeping the original spirit of providing a trans-European consensus based on robust evidence (scored with GRADE methodology), involving professionals on UCDs from nine countries in preparing this consensus. We believe this revised guideline, which has been reviewed by several societies that are involved in the management of UCDs, will have a positive impact on the outcomes of patients by establishing common standards, and spreading and harmonizing good practices. It may also promote the identification of knowledge voids to be filled by future research.
Collapse
Affiliation(s)
- Johannes Häberle
- University Children's Hospital Zurich and Children's Research Centre, Zurich, Switzerland
| | - Alberto Burlina
- Division of Inborn Metabolic Disease, Department of Pediatrics, University Hospital Padua, Padova, Italy
| | - Anupam Chakrapani
- Department of Metabolic Medicine, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK
| | - Marjorie Dixon
- Dietetics, Great Ormond Street Hospital for Children, NHS Trust, London, UK
| | - Daniela Karall
- Clinic for Pediatrics, Division of Inherited Metabolic Disorders, Medical University of Innsbruck, Innsbruck, Austria
| | - Martin Lindner
- University Children's Hospital, Frankfurt am Main, Germany
| | - Hanna Mandel
- Institute of Human Genetics and metabolic disorders, Western Galilee Medical Center, Nahariya, Israel
| | - Diego Martinelli
- Division of Metabolism, Bambino Gesù Children's Hospital, Rome, Italy
| | - Guillem Pintos-Morell
- Centre for Rare Diseases, University Hospital Vall d'Hebron, Barcelona, Spain
- CIBERER_GCV08, Research Institute IGTP, Barcelona, Spain
- Universitat Autònoma de Barcelona, Barcelona, Spain
| | - René Santer
- Department of Pediatrics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Anastasia Skouma
- Institute of Child Health, Agia Sofia Children's Hospital, Athens, Greece
| | - Aude Servais
- Service de Néphrologie et maladies métaboliques adulte Hôpital Necker 149, Paris, France
| | - Galit Tal
- The Ruth Rappaport Children's Hospital, Rambam Medical Center, Haifa, Israel
| | - Vicente Rubio
- Instituto de Biomedicina de Valencia (IBV-CSIC), Centro de Investigación Biomédica en Red para Enfermedades Raras (CIBERER), Valencia, Spain
| | - Martina Huemer
- University Children's Hospital Zurich and Children's Research Centre, Zurich, Switzerland
- Department of Paediatrics, Landeskrankenhaus Bregenz, Bregenz, Austria
| | | |
Collapse
|
9
|
Cavicchi C, Chilleri C, Fioravanti A, Ferri L, Ripandelli F, Costa C, Calabresi P, Prontera P, Pochiero F, Pasquini E, Funghini S, la Marca G, Donati MA, Morrone A. Late-Onset N-Acetylglutamate Synthase Deficiency: Report of a Paradigmatic Adult Case Presenting with Headaches and Review of the Literature. Int J Mol Sci 2018; 19:ijms19020345. [PMID: 29364180 PMCID: PMC5855567 DOI: 10.3390/ijms19020345] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Revised: 01/17/2018] [Accepted: 01/18/2018] [Indexed: 12/30/2022] Open
Abstract
N-acetylglutamate synthase deficiency (NAGSD) is an extremely rare urea cycle disorder (UCD) with few adult cases so far described. Diagnosis of late-onset presentations is difficult and delayed treatment may increase the risk of severe hyperammonemia. We describe a 52-year-old woman with recurrent headaches who experienced an acute onset of NAGSD. As very few papers focus on headaches in UCDs, we also report a literature review of types and pathophysiologic mechanisms of UCD-related headaches. In our case, headaches had been present since puberty (3–4 days a week) and were often accompanied by nausea, vomiting, or behavioural changes. Despite three previous episodes of altered consciousness, ammonia was measured for the first time at 52 years and levels were increased. Identification of the new homozygous c.344C>T (p.Ala115Val) NAGS variant allowed the definite diagnosis of NAGSD. Bioinformatic analysis suggested that an order/disorder alteration of the mutated form could affect the arginine-binding site, resulting in poor enzyme activation and late-onset presentation. After optimized treatment for NAGSD, ammonia and amino acid levels were constantly normal and prevented other headache bouts. The manuscript underlies that headache may be the presenting symptom of UCDs and provides clues for the rapid diagnosis and treatment of late-onset NAGSD.
Collapse
Affiliation(s)
- Catia Cavicchi
- Molecular and Cell Biology Laboratory of Neurometabolic Diseases, Neuroscience Department, Meyer Children's Hospital, 50139 Florence, Italy.
| | - Chiara Chilleri
- Molecular and Cell Biology Laboratory of Neurometabolic Diseases, Neuroscience Department, Meyer Children's Hospital, 50139 Florence, Italy.
| | - Antonella Fioravanti
- Structural Biology Researcher Center, VIB, Vrije Universiteit Brussel, 1050 Brussels, Belgium.
| | - Lorenzo Ferri
- Molecular and Cell Biology Laboratory of Neurometabolic Diseases, Neuroscience Department, Meyer Children's Hospital, 50139 Florence, Italy.
| | | | - Cinzia Costa
- Neurology Unit, Santa Maria della Misericordia Hospital, 06123 Perugia, Italy.
| | - Paolo Calabresi
- Neurology Unit, Santa Maria della Misericordia Hospital, 06123 Perugia, Italy.
| | - Paolo Prontera
- Medical Genetics Unit, Santa Maria della Misericordia Hospital, 06123 Perugia, Italy.
| | - Francesca Pochiero
- Metabolic and Muscular Unit, Neuroscience Department, Meyer Children's Hospital, 50139 Florence, Italy.
| | - Elisabetta Pasquini
- Metabolic and Muscular Unit, Neuroscience Department, Meyer Children's Hospital, 50139 Florence, Italy.
| | - Silvia Funghini
- Newborn Screening, Biochemistry and Pharmacology Laboratory, Neuroscience Department, Meyer Children's Hospital, 50139 Florence, Italy.
| | - Giancarlo la Marca
- Newborn Screening, Biochemistry and Pharmacology Laboratory, Neuroscience Department, Meyer Children's Hospital, 50139 Florence, Italy.
- Department of Experimental and Clinical Biomedical Sciences, University of Florence, 50139 Florence, Italy.
| | - Maria Alice Donati
- Metabolic and Muscular Unit, Neuroscience Department, Meyer Children's Hospital, 50139 Florence, Italy.
| | - Amelia Morrone
- Molecular and Cell Biology Laboratory of Neurometabolic Diseases, Neuroscience Department, Meyer Children's Hospital, 50139 Florence, Italy.
- Department of Neurosciences, Psychology, Drug Research and Child Health (NEUROFARBA), University of Florence, 50139 Florence, Italy.
| |
Collapse
|
10
|
Chapel-Crespo CC, Diaz GA, Oishi K. Efficacy of N-carbamoyl-L-glutamic acid for the treatment of inherited metabolic disorders. Expert Rev Endocrinol Metab 2016; 11:467-473. [PMID: 30034506 PMCID: PMC6054484 DOI: 10.1080/17446651.2016.1239526] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
INTRODUCTION N-carbamoyl-L-glutamic acid (NCG) is a synthetic analogue of N-acetyl glutamate (NAG) that works effectively as a cofactor for carbamoyl phosphate synthase 1 and enhances ureagenesis by activating the urea cycle. NCG (brand name, Carbaglu) was recently approved by the United States Food and Drug Administration (US FDA) for the management of NAGS deficiency and by the European Medicines Agency (EMA) for the treatment of NAGS deficiency as well as for the treatment of hyperammonenia in propionic, methylmalonic and isovaleric acidemias in Europe. AREAS COVERED The history, mechanism of action, and efficacy of this new drug are described. Moreover, clinical utility of NCG in a variety of inborn errors of metabolism with secondary NAGS deficiency is discussed. EXPERT COMMENTARY NCG has favorable pharmacological features including better bioavailability compared to NAG. The clinical use of NCG has proven to be so effective as to make dietary protein restriction unnecessary for patients with NAGS deficiency. It has been also demonstrated to be effective for hyperammonemia secondary to other types of inborn errors of metabolism. NCG may have additional therapeutic potential in conditions such as hepatic hyperammonemic encephalopathy secondary to chemotherapies or other liver pathology.
Collapse
Affiliation(s)
- Cristel C Chapel-Crespo
- Department of Genetics and Genomic Sciences, Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - George A Diaz
- Department of Genetics and Genomic Sciences, Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Kimihiko Oishi
- Department of Genetics and Genomic Sciences, Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| |
Collapse
|
11
|
Al Kaabi EH, El-Hattab AW. N-acetylglutamate synthase deficiency: Novel mutation associated with neonatal presentation and literature review of molecular and phenotypic spectra. Mol Genet Metab Rep 2016; 8:94-8. [PMID: 27570737 PMCID: PMC4992009 DOI: 10.1016/j.ymgmr.2016.08.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2016] [Revised: 08/07/2016] [Accepted: 08/07/2016] [Indexed: 12/30/2022] Open
Abstract
The urea cycle is the main pathway for the disposal of excess nitrogen. Carbamoylphosphate synthetase 1 (CPS1), the first and rate-limiting enzyme of urea cycle, is activated by N-acetylglutamate (NAG), and thus N-acetylglutamate synthase (NAGS) is an essential part of the urea cycle. Although NAGS deficiency is the rarest urea cycle disorder, it is the only one that can be specifically and effectively treated by a drug, N-carbamylglutamate, a stable structural analogous of NAG that activates CPS1. Here we report an infant with NAGS deficiency who presented with neonatal hyperammonemia. She was found to have a novel homozygous splice-site mutation, c.1097-2A>T, in the NAGS gene. We describe the clinical course of this infant, who had rapid response to N-carbamylglutamate treatment. In addition, we reviewed the clinical and molecular spectra of previously reported individuals with NAGS deficiency, which presents in most cases with neonatal hyperammonemia, and in some cases the presentation is later, with a broad spectrum of ages and manifestations. With this broad later-onset phenotypic spectrum, maintaining a high index of suspicion is needed for the early diagnosis of this treatable disease.
Collapse
Affiliation(s)
- Eiman H Al Kaabi
- Pediatrics Department, Tawam Hospital, Al-Ain, United Arab Emirates
| | - Ayman W El-Hattab
- Division of Clinical Genetics and Metabolic Disorders, Pediatrics Department, Tawam Hospital, Al-Ain, United Arab Emirates
| |
Collapse
|
12
|
Sancho-Vaello E, Marco-Marín C, Gougeard N, Fernández-Murga L, Rüfenacht V, Mustedanagic M, Rubio V, Häberle J. Understanding N-Acetyl-L-Glutamate Synthase Deficiency: Mutational Spectrum, Impact of Clinical Mutations on Enzyme Functionality, and Structural Considerations. Hum Mutat 2016; 37:679-94. [DOI: 10.1002/humu.22995] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Accepted: 03/10/2016] [Indexed: 12/13/2022]
Affiliation(s)
| | - Clara Marco-Marín
- Instituto de Biomedicina de Valencia (IBV-CSIC); Valencia Spain
- Group 739, CIBERER, ISCIII; Spain
| | - Nadine Gougeard
- Instituto de Biomedicina de Valencia (IBV-CSIC); Valencia Spain
- Group 739, CIBERER, ISCIII; Spain
| | - Leonor Fernández-Murga
- Instituto de Biomedicina de Valencia (IBV-CSIC); Valencia Spain
- Group 739, CIBERER, ISCIII; Spain
| | - Véronique Rüfenacht
- University Children's Hospital and Children's Research Center; Zurich Switzerland
| | - Merima Mustedanagic
- University Children's Hospital and Children's Research Center; Zurich Switzerland
| | - Vicente Rubio
- Instituto de Biomedicina de Valencia (IBV-CSIC); Valencia Spain
- Group 739, CIBERER, ISCIII; Spain
| | - Johannes Häberle
- University Children's Hospital and Children's Research Center; Zurich Switzerland
| |
Collapse
|
13
|
Hyperammonemia due to Adult-Onset N-Acetylglutamate Synthase Deficiency. JIMD Rep 2016; 31:95-99. [PMID: 27147233 DOI: 10.1007/8904_2016_565] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Revised: 03/25/2016] [Accepted: 03/29/2016] [Indexed: 03/29/2023] Open
Abstract
A 59-year-old woman, with a medical history of intellectual disability after perinatal asphyxia, was admitted because of coma due to hyperammonemia after she was treated for a fracture of the pelvis. The ammonia level was 280 μM. Acquired disorders as explanation for the hyperammonemia were excluded. Metabolic investigations showed an elevated glutamine and alanine and low citrulline, suspect for a urea cycle defect (UCD). Orotic acid could not be demonstrated in urine. DNA investigations were negative for mutations or deletions in the OTC and CPS1 gene, but revealed a homozygous c.603G>C mutation in exon 2 of the N-acetylglutamate synthase (NAGS) gene (NM_153006.2:c.603G>C), which mandates p.Lys201Asn. This is a novel mutation in the NAGS gene.After the diagnosis of NAGS deficiency was made carbamylglutamate was started in a low dose. In combination with mild protein restriction the ammonia level decreased to 26 μM.This is one of the first patients in literature in whom the diagnosis of a UCD is made at such an advanced age. It is important for the adult physician to consider a metabolic disorder at every age.
Collapse
|
14
|
Chaturvedi S, Singh AK, Keshari AK, Maity S, Sarkar S, Saha S. Human Metabolic Enzymes Deficiency: A Genetic Mutation Based Approach. SCIENTIFICA 2016; 2016:9828672. [PMID: 27051561 PMCID: PMC4804091 DOI: 10.1155/2016/9828672] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 01/21/2016] [Accepted: 01/31/2016] [Indexed: 05/30/2023]
Abstract
One of the extreme challenges in biology is to ameliorate the understanding of the mechanisms which emphasize metabolic enzyme deficiency (MED) and how these pretend to have influence on human health. However, it has been manifested that MED could be either inherited as inborn error of metabolism (IEM) or acquired, which carries a high risk of interrupted biochemical reactions. Enzyme deficiency results in accumulation of toxic compounds that may disrupt normal organ functions and cause failure in producing crucial biological compounds and other intermediates. The MED related disorders cover widespread clinical presentations and can involve almost any organ system. To sum up the causal factors of almost all the MED-associated disorders, we decided to embark on a less traveled but nonetheless relevant direction, by focusing our attention on associated gene family products, regulation of their expression, genetic mutation, and mutation types. In addition, the review also outlines the clinical presentations as well as diagnostic and therapeutic approaches.
Collapse
Affiliation(s)
- Swati Chaturvedi
- Department of Pharmaceutical Sciences, Babasaheb Bhimrao Ambedkar University, Raebareli Road, Vidyavihar, Lucknow 226025, India
| | - Ashok K. Singh
- Department of Pharmaceutical Sciences, Babasaheb Bhimrao Ambedkar University, Raebareli Road, Vidyavihar, Lucknow 226025, India
| | - Amit K. Keshari
- Department of Pharmaceutical Sciences, Babasaheb Bhimrao Ambedkar University, Raebareli Road, Vidyavihar, Lucknow 226025, India
| | - Siddhartha Maity
- Department of Pharmaceutical Technology, Jadavpur University, Kolkata 700032, India
| | - Srimanta Sarkar
- Dr. Reddy's Laboratories Limited, Bachupally, Hyderabad, Telangana 502325, India
| | - Sudipta Saha
- Department of Pharmaceutical Sciences, Babasaheb Bhimrao Ambedkar University, Raebareli Road, Vidyavihar, Lucknow 226025, India
| |
Collapse
|
15
|
Abstract
N-acetyl-glutamate synthase (NAGS) deficiency is a rare autosomal recessive urea cycle disorder (UCD) that uncommonly presents in adulthood. Adult presentations of UCDs include; confusional episodes, neuropsychiatric symptoms and encephalopathy. To date, there have been no detailed neurological descriptions of an adult onset presentation of NAGS deficiency. In this review we examine the clinical presentation and management of UCDs with an emphasis on NAGS deficiency. An illustrative case is provided. Plasma ammonia levels should be measured in all adult patients with unexplained encephalopathy, as treatment can be potentially life-saving. Availability of N-carbamylglutamate (NCG; carglumic acid) has made protein restriction largely unnecessary in treatment regimens currently employed. Genetic counselling remains an essential component of management of NAGS.
Collapse
|
16
|
Häberle J, Boddaert N, Burlina A, Chakrapani A, Dixon M, Huemer M, Karall D, Martinelli D, Crespo PS, Santer R, Servais A, Valayannopoulos V, Lindner M, Rubio V, Dionisi-Vici C. Suggested guidelines for the diagnosis and management of urea cycle disorders. Orphanet J Rare Dis 2012; 7:32. [PMID: 22642880 PMCID: PMC3488504 DOI: 10.1186/1750-1172-7-32] [Citation(s) in RCA: 362] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2011] [Accepted: 04/06/2012] [Indexed: 12/11/2022] Open
Abstract
Urea cycle disorders (UCDs) are inborn errors of ammonia detoxification/arginine synthesis due to defects affecting the catalysts of the Krebs-Henseleit cycle (five core enzymes, one activating enzyme and one mitochondrial ornithine/citrulline antiporter) with an estimated incidence of 1:8.000. Patients present with hyperammonemia either shortly after birth (~50%) or, later at any age, leading to death or to severe neurological handicap in many survivors. Despite the existence of effective therapy with alternative pathway therapy and liver transplantation, outcomes remain poor. This may be related to underrecognition and delayed diagnosis due to the nonspecific clinical presentation and insufficient awareness of health care professionals because of disease rarity. These guidelines aim at providing a trans-European consensus to: guide practitioners, set standards of care and help awareness campaigns. To achieve these goals, the guidelines were developed using a Delphi methodology, by having professionals on UCDs across seven European countries to gather all the existing evidence, score it according to the SIGN evidence level system and draw a series of statements supported by an associated level of evidence. The guidelines were revised by external specialist consultants, unrelated authorities in the field of UCDs and practicing pediatricians in training. Although the evidence degree did hardly ever exceed level C (evidence from non-analytical studies like case reports and series), it was sufficient to guide practice on both acute and chronic presentations, address diagnosis, management, monitoring, outcomes, and psychosocial and ethical issues. Also, it identified knowledge voids that must be filled by future research. We believe these guidelines will help to: harmonise practice, set common standards and spread good practices with a positive impact on the outcomes of UCD patients.
Collapse
Affiliation(s)
- Johannes Häberle
- University Children’s Hospital Zurich and Children’s Research Centre, Zurich, 8032, Switzerland
| | - Nathalie Boddaert
- Radiologie Hopital Necker, Service Radiologie Pediatrique, 149 Rue De Sevres, Paris 15, 75015, France
| | - Alberto Burlina
- Department of Pediatrics, Division of Inborn Metabolic Disease, University Hospital Padua, Via Giustiniani 3, Padova, 35128, Italy
| | - Anupam Chakrapani
- Birmingham Children’s Hospital NHS Foundation Trust, Steelhouse Lane, Birmingham, B4 6NH, United Kingdom
| | - Marjorie Dixon
- Dietetic Department, Great Ormond Street Hospital for Children, NHS Foundation Trust, London, WC1N 3JH, United Kingdom
| | - Martina Huemer
- Kinderabteilung, LKH Bregenz, Carl-Pedenz-Strasse 2, Bregenz, A-6900, Austria
| | - Daniela Karall
- University Children’s Hospital, Medical University Innsbruck, Anichstrasse 35, Innsbruck, 6020, Austria
| | - Diego Martinelli
- Division of Metabolism, Bambino Gesù Children’s Hospital, IRCCS, Piazza S. Onofrio 4, Rome, I-00165, Italy
| | | | - René Santer
- Universitätsklinikum Hamburg Eppendorf, Klinik für Kinder- und Jugendmedizin, Martinistr. 52, Hamburg, 20246, Germany
| | - Aude Servais
- Service de Néphrologie et maladies métaboliques adulte Hôpital Necker 149, rue de Sèvres, Paris, 75015, France
| | - Vassili Valayannopoulos
- Reference Center for Inherited Metabolic Disorders (MaMEA), Hopital Necker-Enfants Malades, 149 Rue de Sevres, Paris, 75015, France
| | - Martin Lindner
- University Children’s Hospital, Im Neuenheimer Feld 430, Heidelberg, 69120, Germany
| | - Vicente Rubio
- Instituto de Biomedicina de Valencia del Consejo Superior de Investigaciones Científicas (IBV-CSIC) and Centro de Investigación Biomédica en Red para Enfermedades Raras (CIBERER), C/ Jaume Roig 11, Valencia, 46010, Spain
| | - Carlo Dionisi-Vici
- Division of Metabolism, Bambino Gesù Children’s Hospital, IRCCS, Piazza S. Onofrio 4, Rome, I-00165, Italy
| |
Collapse
|
17
|
Häberle J. Carglumic acid for the treatment of N-acetylglutamate synthase deficiency and acute hyperammonemia. Expert Rev Endocrinol Metab 2012; 7:263-271. [PMID: 30780843 DOI: 10.1586/eem.12.17] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Carglumic acid is a structural analog and the first registered synthetic form of the naturally occurring allosteric activator of the urea cycle, N-acetylglutamate (NAG), which is the product of the enzyme NAG synthase (NAGS). Because NAG is essential for the function of carbamoylphosphate synthetase 1 as the first step of the urea cycle, a decreased availability of NAG due to primary or secondary defects of NAGS will affect ammonia detoxification in the urea cycle. Carglumic acid (Carbaglu®, Orphan Europe SARL, Paris, France) is approved for the acute and long-term treatment of primary defects of NAGS in Europe and the USA. In addition, it is approved in Europe for the treatment of acute hyperammonemia in patients with specific organic acidurias that can lead to NAG deficiency secondary to inhibition of NAGS. This article reviews the use of carglumic acid for both approved indications and considers the potential of this compound for acute hyperammonemias in general.
Collapse
Affiliation(s)
- Johannes Häberle
- a University Children's Hospital, Division of Metabolism, Children's Research Center, Steinwiesstrasse 75, CH-8032 Zürich, Switzerland.
| |
Collapse
|
18
|
Heibel SK, Ah Mew N, Caldovic L, Daikhin Y, Yudkoff M, Tuchman M. N-carbamylglutamate enhancement of ureagenesis leads to discovery of a novel deleterious mutation in a newly defined enhancer of the NAGS gene and to effective therapy. Hum Mutat 2011; 32:1153-60. [PMID: 21681857 DOI: 10.1002/humu.21553] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2011] [Accepted: 06/01/2011] [Indexed: 11/09/2022]
Abstract
N-acetylglutamate synthase (NAGS) catalyzes the conversion of glutamate and acetyl-CoA to NAG, the essential allosteric activator of carbamyl phosphate synthetase I, the first urea cycle enzyme in mammals. A 17-year-old female with recurrent hyperammonemia attacks, the cause of which remained undiagnosed for 8 years in spite of multiple molecular and biochemical investigations, showed markedly enhanced ureagenesis (measured by isotope incorporation) in response to N-carbamylglutamate (NCG). This led to sequencing of the regulatory regions of the NAGS gene and identification of a deleterious single-base substitution in the upstream enhancer. The homozygous mutation (c.-3064C>A), affecting a highly conserved nucleotide within the hepatic nuclear factor 1 (HNF-1) binding site, was not found in single nucleotide polymorphism databases and in a screen of 1,086 alleles from a diverse population. Functional assays demonstrated that this mutation decreases transcription and binding of HNF-1 to the NAGS gene, while a consensus HNF-1 binding sequence enhances binding to HNF-1 and increases transcription. Oral daily NCG therapy restored ureagenesis in this patient, normalizing her biochemical markers, and allowing discontinuation of alternate pathway therapy and normalization of her diet with no recurrence of hyperammonemia. Inc.
Collapse
Affiliation(s)
- Sandra K Heibel
- Research Center for Genetic Medicine, Children's National Medical Center, The George Washington University, Washington, DC, USA
| | | | | | | | | | | |
Collapse
|
19
|
Ah Mew N, Caldovic L. N-acetylglutamate synthase deficiency: an insight into the genetics, epidemiology, pathophysiology, and treatment. APPLICATION OF CLINICAL GENETICS 2011; 4:127-35. [PMID: 23776373 PMCID: PMC3681184 DOI: 10.2147/tacg.s12702] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The conversion of ammonia into urea by the human liver requires the coordinated function of the 6 enzymes and 2 transporters of the urea cycle. The initial and rate-limiting enzyme of the urea cycle, carbamylphosphate synthetase 1 (CPS1), requires an allosteric activator, N-acetylglutamate (NAG). The formation of this unique cofactor from glutamate and acetyl Coenzyme-A is catalyzed by N-acetylglutamate synthase (NAGS). An absence of NAG as a consequence of NAGS deficiency may compromise flux through CPS1 and result in hyperammonemia. The NAGS gene encodes a 528-amino acid protein, consisting of a C-terminal catalytic domain, a variable segment, and an N-terminal mitochondrial targeting signal. Only 22 mutations in the NAGS gene have been reported to date, mostly in the catalytic domain. NAGS is primarily expressed in the liver and intestine. However, it is also surprisingly expressed in testis, stomach and spleen, and during early embryonic development at levels not concordant with the expression of other urea cycle enzymes, CPS1, or ornithine transcarbamylase. The purpose of NAGS expression in these tissues, and its significance to NAGS deficiency is as yet unknown. Inherited NAGS deficiency is the rarest of the urea cycle disorders, and we review the currently reported 34 cases. Treatment of NAGS deficiency with N-carbamyglutamate, a stable analog of NAG, can restore deficient urea cycle function and normalize blood ammonia in affected patients.
Collapse
Affiliation(s)
- Nicholas Ah Mew
- Center for Genetic Medicine Research, Children's Research institute, Children's National Medical Center, Washington DC, USA
| | | |
Collapse
|
20
|
Häberle J. Role of carglumic acid in the treatment of acute hyperammonemia due to N-acetylglutamate synthase deficiency. Ther Clin Risk Manag 2011; 7:327-32. [PMID: 21941437 PMCID: PMC3176164 DOI: 10.2147/tcrm.s12703] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
N-acetylglutamate synthase (NAGS) deficiency is a rare inborn error of metabolism affecting ammonia detoxification in the urea cycle. The product of NAGS is N-acetylglutamate which is the absolutely required allosteric activator of the first urea cycle enzyme carbamoylphosphate synthetase 1. In defects of NAGS, the urea cycle function can be severely affected resulting in fatal hyperammonemia in neonatal patients or at any later stage in life. NAGS deficiency can be treated with a structural analog of N-acetylglutamate, N-carbamyl-L-glutamate, which is available for enteral use as a licensed drug. Since NAGS deficiency is an extremely rare disorder, reports on the use of N-carbamyl-L-glutamate are mainly based on single patients. According to these, the drug is very effective in treating acute hyperammonemia by avoiding the need for detoxification during the acute metabolic decompensation. Also during long-term treatment, N-carbamyl-L-glutamate is effective in maintaining normal plasma ammonia levels and avoiding the need for additional drug therapy or protein-restricted diet. Open questions remain which concern the optimal dosage in acute and long-term use of N-carbamyl-L-glutamate and potential additional disorders in which the drug might also be effective in treating acute hyperammonemia. This review focuses on the role of N-carbamyl-L-glutamate for the treatment of acute hyperammonemia due to primary NAGS deficiency but will briefly discuss the current knowledge on the role of N-carbamyl-L-glutamate for treatment of secondary NAGS deficiencies.
Collapse
Affiliation(s)
- Johannes Häberle
- Kinderspital Zürich, Abteilung Stoffwechsel, Zürich, Switzerland
| |
Collapse
|
21
|
Daniotti M, la Marca G, Fiorini P, Filippi L. New developments in the treatment of hyperammonemia: emerging use of carglumic acid. Int J Gen Med 2011; 4:21-8. [PMID: 21403788 PMCID: PMC3056327 DOI: 10.2147/ijgm.s10490] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Hyperammonemia is a true neonatal emergency with high toxicity for the central nervous system and developmental delay. The causes of neonatal hyperammonemia are genetic defects of urea cycle enzymes, organic acidemias, lysinuric protein intolerance, hyperammonemia-hyperornithinemia- homocitrullinemia syndrome, transient hyperammonemia of the newborn, and congenital hyperinsulinism with hyperammonemia. In some of these conditions the high blood ammonia levels are due to the reduction of N-acetylglutamate, an essential cofactor necessary for the function of the urea cycle, or to the reduction of carbamoyl-phosphate synthase-I activity. In these cases, N-carbamylglutamate (carglumic acid) can be administered together with the conventional therapy. Carglumic acid is an analog of N-acetylglutamate that has a direct action on carbamoyl-phosphate synthase-I. Its effects are reactivation of the urea cycle and reduction of plasma ammonia levels. As a consequence it improves the traditional treatment, avoiding the need of hemodialysis and peritoneal dialysis. In this review we evaluate the possible field of application of carglumic acid and its effectiveness and safety.
Collapse
Affiliation(s)
- Marta Daniotti
- Neonatal Intensive Care Unit, Department of Perinatal Medicine, “A. Meyer” University Children’s Hospital, Florence, Italy
| | - Giancarlo la Marca
- Mass Spectrometry, Clinical Chemistry and Pharmacology Laboratory, Neuroscience Department, “A. Meyer” University Children’s Hospital, Florence, Italy
| | - Patrizio Fiorini
- Neonatal Intensive Care Unit, Department of Perinatal Medicine, “A. Meyer” University Children’s Hospital, Florence, Italy
| | - Luca Filippi
- Neonatal Intensive Care Unit, Department of Perinatal Medicine, “A. Meyer” University Children’s Hospital, Florence, Italy
| |
Collapse
|
22
|
Caldovic L, Mew NA, Shi D, Morizono H, Yudkoff M, Tuchman M. N-acetylglutamate synthase: structure, function and defects. Mol Genet Metab 2010; 100 Suppl 1:S13-9. [PMID: 20303810 PMCID: PMC2876818 DOI: 10.1016/j.ymgme.2010.02.018] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Accepted: 02/22/2010] [Indexed: 11/26/2022]
Abstract
N-acetylglutamate (NAG) is a unique enzyme cofactor, essential for liver ureagenesis in mammals while it is the first committed substrate for de novo arginine biosynthesis in microorganisms and plants. The enzyme that produces NAG from glutamate and CoA, NAG synthase (NAGS), is allosterically inhibited by arginine in microorganisms and plants and activated in mammals. This transition of the allosteric effect occurred when tetrapods moved from sea to land. The first mammalian NAGS gene (from mouse) was cloned in 2002 and revealed significant differences from the NAGS ortholog in microorganisms. Almost all NAGS genes possess a C-terminus transferase domain in which the catalytic activity resides and an N-terminus kinase domain where arginine binds. The three-dimensional structure of NAGS shows two distinctly folded domains. The kinase domain binds arginine while the acetyltransferase domain contains the catalytic site. NAGS deficiency in humans leads to hyperammonemia and can be primary, due to mutations in the NAGS gene or secondary due to other mitochondrial aberrations that interfere with the normal function of the same enzyme. For either condition, N-carbamylglutamate (NCG), a stable functional analog of NAG, was found to either restore or improve the deficient urea-cycle function.
Collapse
Affiliation(s)
- Ljubica Caldovic
- Children’s Research Institute, Children’s National Medical Center, 111 Michigan Ave NW, The George Washington University, Washington, DC, 20010, USA
| | - Nicholas Ah Mew
- Children’s Research Institute, Children’s National Medical Center, 111 Michigan Ave NW, The George Washington University, Washington, DC, 20010, USA
| | - Dashuang Shi
- Children’s Research Institute, Children’s National Medical Center, 111 Michigan Ave NW, The George Washington University, Washington, DC, 20010, USA
| | - Hiroki Morizono
- Children’s Research Institute, Children’s National Medical Center, 111 Michigan Ave NW, The George Washington University, Washington, DC, 20010, USA
| | - Marc Yudkoff
- Children’s Hospital of Philadelphia, 34th Street and Civic Center Blvd, Philadelphia, PA, 19104; Dept. of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104, USA
| | - Mendel Tuchman
- Children’s Research Institute, Children’s National Medical Center, 111 Michigan Ave NW, The George Washington University, Washington, DC, 20010, USA
| |
Collapse
|
23
|
Yudkoff M, Mew NA, Payan I, Daikhin Y, Nissim I, Nissim I, Tuchman M. Effects of a single dose of N-carbamylglutamate on the rate of ureagenesis. Mol Genet Metab 2009; 98:325-30. [PMID: 19660971 PMCID: PMC2784258 DOI: 10.1016/j.ymgme.2009.07.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2009] [Revised: 07/07/2009] [Accepted: 07/08/2009] [Indexed: 10/20/2022]
Abstract
We studied the effect on ureagenesis of a single dose of N-carbamylglutamate (NCG) in healthy young adults who received a constant infusion (300 min) of NaH(13)CO(3). Isotope ratio-mass spectrometry was used to measure the appearance of label in [(13)C]urea. At 90 min after initiating the H(13)CO3-infusion each subject took a single dose of NCG (50 mg/kg). In 5/6 studies the administration of NCG increased the formation of [(13)C]urea. Treatment with NCG significantly diminished the concentration of blood alanine, but not that of glutamine or arginine. The blood glucose concentration was unaffected by NCG administration. No untoward side effects were observed. The data indicate that treatment with NCG stimulates ureagenesis and could be useful in clinical settings of acute hyperammonemia of various etiologies.
Collapse
Affiliation(s)
- Marc Yudkoff
- Children’s Hospital of Philadelphia; Dept. of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104, USA
| | - Nicholas Ah Mew
- Research Center for Genetic Medicine, Children's National Medical Center, The George Washington University, Washington, D. C. 20010, USA
| | - Irma Payan
- Children’s Hospital of Philadelphia; Dept. of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104, USA
| | - Yevgeny Daikhin
- Children’s Hospital of Philadelphia; Dept. of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104, USA
| | - Ilana Nissim
- Children’s Hospital of Philadelphia; Dept. of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104, USA
| | - Itzhak Nissim
- Children’s Hospital of Philadelphia; Dept. of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104, USA
| | - Mendel Tuchman
- Research Center for Genetic Medicine, Children's National Medical Center, The George Washington University, Washington, D. C. 20010, USA
| |
Collapse
|
24
|
Neill MA, Aschner J, Barr F, Summar ML. Quantitative RT-PCR comparison of the urea and nitric oxide cycle gene transcripts in adult human tissues. Mol Genet Metab 2009; 97:121-7. [PMID: 19345634 PMCID: PMC2680466 DOI: 10.1016/j.ymgme.2009.02.009] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/19/2009] [Accepted: 02/21/2009] [Indexed: 01/20/2023]
Abstract
The urea cycle and nitric oxide cycle play significant roles in complex biochemical and physiologic reactions. These cycles have distinct biochemical goals including the clearance of waste nitrogen; the production of the intermediates ornithine, citrulline, and arginine for the urea cycle; and the production of nitric oxide for the nitric oxide pathway. Despite their disparate functions, the two pathways share two enzymes, argininosuccinic acid synthase and argininosuccinic acid lyase, and a transporter, citrin. Studying the gene expression of these enzymes is paramount in understanding these complex biochemical pathways. Here, we examine the expression of genes involved in the urea cycle and the nitric oxide cycle in a panel of eleven different tissue samples obtained from individual adults without known inborn errors of metabolism. In this study, the pattern of co-expressed enzymes provides a global view of the metabolic activity of the urea and nitric oxide cycles in human tissues. Our results show that these transcripts are differentially expressed in different tissues. Using the co-expression profiles, we discovered that the combination of expression of enzyme transcripts as detected in our study, might serve to fulfill specific physiologic function(s) including urea production/nitrogen removal, arginine/citrulline production, nitric oxide production, and ornithine production. Our study reveals the importance of studying not only the expression profile of an enzyme of interest, but also studying the expression profiles of the other enzymes involved in a particular pathway so as to better understand the context of expression. The tissue patterns we observed highlight the variety of important functions of these enzymes and provides insight into the many clinical observations that result from their disruption. These results have implications for the management of urea cycle patients and raise considerations for the care of those patients receiving liver transplants. Finally, this work reaffirms the concept that the co-expression of a few genes can significantly impact complex biochemical and physiologic processes.
Collapse
Affiliation(s)
- Meaghan Anne Neill
- Center for Human Genetics Research, Vanderbilt University Medical Center, Nashville, TN
| | - Judy Aschner
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN
| | - Frederick Barr
- Center for Human Genetics Research, Vanderbilt University Medical Center, Nashville, TN
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN
| | - Marshall L. Summar
- Center for Human Genetics Research, Vanderbilt University Medical Center, Nashville, TN
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN
| |
Collapse
|
25
|
Tuchman M, Caldovic L, Daikhin Y, Horyn O, Nissim I, Nissim I, Korson M, Burton B, Yudkoff M. N-carbamylglutamate markedly enhances ureagenesis in N-acetylglutamate deficiency and propionic acidemia as measured by isotopic incorporation and blood biomarkers. Pediatr Res 2008; 64:213-7. [PMID: 18414145 PMCID: PMC2640836 DOI: 10.1203/pdr.0b013e318179454b] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
N-acetylglutamate (NAG) is an endogenous essential cofactor for conversion of ammonia to urea in the liver. Deficiency of NAG causes hyperammonemia and occurs because of inherited deficiency of its producing enzyme, NAG synthase (NAGS), or interference with its function by short fatty acid derivatives. N-carbamylglutamate (NCG) can ameliorate hyperammonemia from NAGS deficiency and propionic and methylmalonic acidemia. We developed a stable isotope (13)C tracer method to measure ureagenesis and to evaluate the effect of NCG in humans. Seventeen healthy adults were investigated for the incorporation of (13)C label into urea. [(13)C]urea appeared in the blood within minutes, reaching maximum by 100 min, whereas breath (13)CO(2) reached a maximum by 60 min. A patient with NAGS deficiency showed very little urea labeling before treatment with NCG and normal labeling thereafter. Correspondingly, plasma levels of ammonia and glutamine decreased markedly and urea tripled after NCG treatment. Similarly, in a patient with propionic acidemia, NCG treatment resulted in a marked increase in urea labeling and decrease in glutamine, alanine, and glycine. These results provide a reliable method for measuring the effect of NCG on nitrogen metabolism and strongly suggest that NCG could be an effective treatment for inherited and secondary NAGS deficiency.
Collapse
Affiliation(s)
- Mendel Tuchman
- Children's Research Institute, Children's National Medical Center, George Washington University, Washington, DC 20052, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
26
|
Deignan JL, Cederbaum SD, Grody WW. Contrasting features of urea cycle disorders in human patients and knockout mouse models. Mol Genet Metab 2008; 93:7-14. [PMID: 17933574 PMCID: PMC2692509 DOI: 10.1016/j.ymgme.2007.08.123] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2007] [Revised: 08/19/2007] [Accepted: 08/19/2007] [Indexed: 10/22/2022]
Abstract
The urea cycle exists for the removal of excess nitrogen from the body. Six separate enzymes comprise the urea cycle, and a deficiency in any one of them causes a urea cycle disorder (UCD) in humans. Arginase is the only urea cycle enzyme with an alternate isoform, though no known human disorder currently exists due to a deficiency in the second isoform. While all of the UCDs usually present with hyperammonemia in the first few days to months of life, most disorders are distinguished by a characteristic profile of plasma amino acid alterations that can be utilized for diagnosis. While enzyme assay is possible, an analysis of the underlying mutation is preferable for an accurate diagnosis. Mouse models for each of the urea cycle disorders exist (with the exception of NAGS deficiency), and for almost all of them, their clinical and biochemical phenotypes rather closely resemble the phenotypes seen in human patients. Consequently, all of the current mouse models are highly useful for future research into novel pharmacological and dietary treatments and gene therapy protocols for the management of urea cycle disorders.
Collapse
Affiliation(s)
- Joshua L. Deignan
- Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA
- The Mental Retardation Research Center, David Geffen School of Medicine at UCLA, Los Angeles, CA
| | - Stephen D. Cederbaum
- Department of Psychiatry, David Geffen School of Medicine at UCLA, Los Angeles, CA
- Department of Pediatrics, David Geffen School of Medicine at UCLA, Los Angeles, CA
- Department of Human Genetics, David Geffen School of Medicine at UCLA, Los Angeles, CA
- The Mental Retardation Research Center, David Geffen School of Medicine at UCLA, Los Angeles, CA
| | - Wayne W. Grody
- Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA
- Department of Pediatrics, David Geffen School of Medicine at UCLA, Los Angeles, CA
- Department of Human Genetics, David Geffen School of Medicine at UCLA, Los Angeles, CA
- The Mental Retardation Research Center, David Geffen School of Medicine at UCLA, Los Angeles, CA
| |
Collapse
|
27
|
Abstract
Patients experiencing acute elevations of ammonia present to the ICU with encephalopathy, which may progress quickly to cerebral herniation. Patient survival requires immediate treatment of intracerebral hypertension and the reduction of ammonia levels. When hyperammonemia is not thought to be the result of liver failure, treatment for an occult disorder of metabolism must begin prior to the confirmation of an etiology. This article reviews ammonia metabolism, the effects of ammonia on the brain, the causes of hyperammonemia, and the diagnosis of inborn errors of metabolism in adult patients.
Collapse
Affiliation(s)
- Alison S Clay
- Department of Surgery and Medicine, Duke University Medical Center, Box 2945, Durham, NC 27710, USA.
| | | |
Collapse
|
28
|
Caldovic L, Morizono H, Tuchman M. Mutations and polymorphisms in the human N-acetylglutamate synthase (NAGS) gene. Hum Mutat 2007; 28:754-9. [PMID: 17421020 DOI: 10.1002/humu.20518] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
N-acetylglutamate synthase (NAGS) deficiency, an autosomal recessive disorder, is the last urea cycle disorder for which molecular testing became available. This is the first comprehensive report of 21 mutations that cause NAGS deficiency and of commonly found polymorphisms in the NAGS gene. Five mutations are reported here for the first time. A total of 10 disease-causing mutations are associated with acute neonatal hyperammonemia; the remaining mutations were found in patients with late onset disease. Residual enzymatic activities are included in this report and the deleterious effects of eight mutations were confirmed by expression studies. Mutations in the NAGS gene are distributed throughout its reading frame. No mutations have been found in exon 1, which encodes for the putative mitochondrial targeting signal and variable segment of NAGS. Three polymorphisms have been found. Early, accurate, and specific diagnosis of NAGS deficiency is critical since this condition can be successfully treated with N-carbamylglutamate (NCG, Carbaglu; Orphan Europe). Treatment with NCG should be initiated as soon as a patient is suspected of having NAGS deficiency. Molecular testing represents the most reliable method of diagnosis.
Collapse
Affiliation(s)
- Ljubica Caldovic
- Children's Research Institute, Children's National Medical Center, George Washington University, Washington, DC 20010, USA.
| | | | | |
Collapse
|
29
|
A novel bifunctional N-acetylglutamate synthase-kinase from Xanthomonas campestris that is closely related to mammalian N-acetylglutamate synthase. BMC BIOCHEMISTRY 2007; 8:4. [PMID: 17425781 PMCID: PMC1865377 DOI: 10.1186/1471-2091-8-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/27/2006] [Accepted: 04/10/2007] [Indexed: 11/17/2022]
Abstract
Background In microorganisms and plants, the first two reactions of arginine biosynthesis are catalyzed by N-acetylglutamate synthase (NAGS) and N-acetylglutamate kinase (NAGK). In mammals, NAGS produces an essential activator of carbamylphosphate synthetase I, the first enzyme of the urea cycle, and no functional NAGK homolog has been found. Unlike the other urea cycle enzymes, whose bacterial counterparts could be readily identified by their sequence conservation with arginine biosynthetic enzymes, mammalian NAGS gene was very divergent, making it the last urea cycle gene to be discovered. Limited sequence similarity between E. coli NAGS and fungal NAGK suggests that bacterial and eukaryotic NAGS, and fungal NAGK arose from the fusion of genes encoding an ancestral NAGK (argB) and an acetyltransferase. However, mammalian NAGS no longer retains any NAGK catalytic activity. Results We identified a novel bifunctional N-acetylglutamate synthase and kinase (NAGS-K) in the Xanthomonadales order of gamma-proteobacteria that appears to resemble this postulated primordial fusion protein. Phylogenetic analysis indicated that xanthomonad NAGS-K is more closely related to mammalian NAGS than to other bacterial NAGS. We cloned the NAGS-K gene from Xanthomonas campestis, and characterized the recombinant NAGS-K protein. Mammalian NAGS and its bacterial homolog have similar affinities for substrates acetyl coenzyme A and glutamate as well as for their allosteric regulator arginine. Conclusion The close phylogenetic relationship and similar biochemical properties of xanthomonad NAGS-K and mammalian NAGS suggest that we have identified a close relative to the bacterial antecedent of mammalian NAGS and that the enzyme from X. campestris could become a good model for mammalian NAGS in structural, biochemical and biophysical studies.
Collapse
|
30
|
Caldovic L, Lopez GY, Haskins N, Panglao M, Shi D, Morizono H, Tuchman M. Biochemical properties of recombinant human and mouse N-acetylglutamate synthase. Mol Genet Metab 2006; 87:226-32. [PMID: 16321554 DOI: 10.1016/j.ymgme.2005.10.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/12/2005] [Revised: 10/19/2005] [Accepted: 10/20/2005] [Indexed: 11/21/2022]
Abstract
N-Acetylglutamate synthase (NAGS, EC 2.3.1.1) is a mitochondrial enzyme that catalyzes the formation of N-acetylglutamate (NAG) from glutamate and acetylcoenzyme A. NAG is an obligatory activator of carbamylphosphate I (CPSI), the first and a rate limiting enzyme of ureagenesis. The enzymatic activity of NAGS increases in the presence of arginine. Since the level of NAGS activity depends on the concentrations of two amino acids, glutamate and arginine, and it supplies the essential cofactor for CPSI, NAGS may play an important role in the regulation of ureagenesis. The amino acid sequences of human and mouse NAGS consist of three regions with different degrees of conservation: the mitochondrial targeting signal (MTS), the variable domain, and the conserved domain. Removal of the MTS results in mature NAGS (NAGS-M) while removal of the MTS and the variable domain results in conserved NAGS (NAGS-C). The biochemical properties of purified recombinant human and mouse NAGS-M and NAGS-C were determined in this study with the goal of better understanding the role of the variable domain in NAGS function. The activity of all four proteins doubled in the presence of arginine, while the affinities for substrates changed less than two fold. The turnover numbers of NAGS-C are double those of NAGS-M proteins. Processing of NAGS-M to form NAGS-C results in an enzyme with higher catalytic activity and could play a role in the regulation of NAG production, CPSI function, and urea synthesis.
Collapse
Affiliation(s)
- Ljubica Caldovic
- Children's Research Institute, Children's National Medical Center, The George Washington University, Washington, DC 20010, USA
| | | | | | | | | | | | | |
Collapse
|