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Adam S, Almeida MF, Assoun M, Baruteau J, Bernabei SM, Bigot S, Champion H, Daly A, Dassy M, Dawson S, Dixon M, Dokoupil K, Dubois S, Dunlop C, Evans S, Eyskens F, Faria A, Favre E, Ferguson C, Goncalves C, Gribben J, Heddrich-Ellerbrok M, Jankowski C, Janssen-Regelink R, Jouault C, Laguerre C, Le Verge S, Link R, Lowry S, Luyten K, Macdonald A, Maritz C, McDowell S, Meyer U, Micciche A, Robert M, Robertson LV, Rocha JC, Rohde C, Saruggia I, Sjoqvist E, Stafford J, Terry A, Thom R, Vande Kerckhove K, van Rijn M, van Teeffelen-Heithoff A, Wegberg AV, van Wyk K, Vasconcelos C, Vestergaard H, Webster D, White FJ, Wildgoose J, Zweers H. Dietary management of urea cycle disorders: European practice. Mol Genet Metab 2013; 110:439-45. [PMID: 24113687 DOI: 10.1016/j.ymgme.2013.09.003] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2013] [Revised: 09/04/2013] [Accepted: 09/06/2013] [Indexed: 12/30/2022]
Abstract
BACKGROUND There is no published data comparing dietary management of urea cycle disorders (UCD) in different countries. METHODS Cross-sectional data from 41 European Inherited Metabolic Disorder (IMD) centres (17 UK, 6 France, 5 Germany, 4 Belgium, 4 Portugal, 2 Netherlands, 1 Denmark, 1 Italy, 1 Sweden) was collected by questionnaire describing management of patients with UCD on prescribed protein restricted diets. RESULTS Data for 464 patients: N-acetylglutamate synthase (NAGS) deficiency, n=10; carbamoyl phosphate synthetase (CPS1) deficiency, n=29; ornithine transcarbamoylase (OTC) deficiency, n=214; citrullinaemia, n=108; argininosuccinic aciduria (ASA), n=80; arginase deficiency, n=23 was reported. The majority of patients (70%; n=327) were aged 0-16y and 30% (n=137) >16y. Prescribed median protein intake/kg body weight decreased with age with little variation between disorders. The UK tended to give more total protein than other European countries particularly in infancy. Supplements of essential amino acids (EAA) were prescribed for 38% [n=174] of the patients overall, but were given more commonly in arginase deficiency (74%), CPS (48%) and citrullinaemia (46%). Patients in Germany (64%), Portugal (67%) and Sweden (100%) were the most frequent users of EAA. Only 18% [n=84] of patients were prescribed tube feeds, most commonly for CPS (41%); and 21% [n=97] were prescribed oral energy supplements. CONCLUSIONS Dietary treatment for UCD varies significantly between different conditions, and between and within European IMD centres. Further studies examining the outcome of treatment compared with the type of dietary therapy and nutritional support received are required.
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Affiliation(s)
- S Adam
- Royal Hospital for Sick Children, Glasgow Royal Infirmary, Glasgow, UK
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Senkevitch E, Cabrera-Luque J, Morizono H, Caldovic L, Tuchman M. A novel biochemically salvageable animal model of hyperammonemia devoid of N-acetylglutamate synthase. Mol Genet Metab 2012; 106:160-8. [PMID: 22503289 PMCID: PMC3356441 DOI: 10.1016/j.ymgme.2012.03.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Revised: 03/09/2012] [Accepted: 03/09/2012] [Indexed: 02/05/2023]
Abstract
All knockout mouse models of urea cycle disorders die in the neonatal period or shortly thereafter. Since N-acetylglutamate synthase (NAGS) deficiency in humans can be effectively treated with N-carbamyl-l-glutamate (NCG), we sought to develop a mouse model of this disorder that could be rescued by biochemical intervention, reared to adulthood, reproduce, and become a novel animal model for hyperammonemia. Founder NAGS knockout heterozygous mice were obtained from the trans-NIH Knock-Out Mouse Project. Genotyping of the mice was performed by PCR and confirmed by Western blotting of liver and intestine. NCG and L-citrulline (Cit) were used to rescue the NAGS knockout homozygous (Nags(-/-)) pups and the rescued animals were characterized. We observed an 85% survival rate of Nags(-/-) mice when they were given intraperitoneal injections with NCG and Cit during the newborn period until weaning and supplemented subsequently with both compounds in their drinking water. This regimen has allowed for normal development, apparent health, and reproduction. Interruption of this rescue intervention resulted in the development of severe hyperammonemia and death within 48 h. In addition to hyperammonemia, interruption of rescue supplementation was associated with elevated plasma glutamine, glutamate, and lysine, and reduced citrulline, arginine, ornithine and proline levels. We conclude that NAGS deprived mouse model has been developed which can be rescued by NCG and Cit and reared to reproduction and beyond. This biochemically salvageable mouse model recapitulates the clinical phenotype of proximal urea cycle disorders and can be used as a reliable model of induced hyperammonemia by manipulating the administration of the rescue compounds.
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Affiliation(s)
- Emilee Senkevitch
- Research Center for Genetic Medicine, Children’s National Medical Center, Washington DC, USA
- Biological Sciences Program, University of Maryland, College Park, Maryland, USA
| | - Juan Cabrera-Luque
- Research Center for Genetic Medicine, Children’s National Medical Center, Washington DC, USA
| | - Hiroki Morizono
- Research Center for Genetic Medicine, Children’s National Medical Center, Washington DC, USA
| | - Ljubica Caldovic
- Research Center for Genetic Medicine, Children’s National Medical Center, Washington DC, USA
| | - Mendel Tuchman
- Research Center for Genetic Medicine, Children’s National Medical Center, Washington DC, USA
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Yudkoff M, Ah Mew N, Daikhin Y, Horyn O, Nissim I, Nissim I, Payan I, Tuchman M. Measuring in vivo ureagenesis with stable isotopes. Mol Genet Metab 2010; 100 Suppl 1:S37-41. [PMID: 20338795 PMCID: PMC2858793 DOI: 10.1016/j.ymgme.2010.02.017] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2010] [Accepted: 02/21/2010] [Indexed: 11/16/2022]
Abstract
Stable isotopes have been an invaluable adjunct to biomedical research for more than 70years. Indeed, the isotopic approach has revolutionized our understanding of metabolism, revealing it to be an intensely dynamic process characterized by an unending cycle of synthesis and degradation. Isotopic studies have taught us that the urea cycle is intrinsic to such dynamism, since it affords a capacious mechanism by which to eliminate waste nitrogen when rates of protein degradation (or dietary protein intake) are especially high. Isotopes have enabled an appreciation of the degree to which ureagenesis is compromised in patients with urea cycle defects. Indeed, isotopic studies of urea cycle flux correlate well with the severity of cognitive impairment in these patients. Finally, the use of isotopes affords an ideal tool with which to gauge the efficacy of therapeutic interventions to augment residual flux through the cycle.
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Affiliation(s)
- Marc Yudkoff
- Children's Hospital of Philadelphia, Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
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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] [What about the content of this article? (0)] [Affiliation(s)] [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.
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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
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Carglumic acid: a second look. Confirmed progress in a rare urea cycle disorder. Prescrire Int 2008; 17:50-1. [PMID: 18516804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
(1) N-acetylglutamate synthase deficiency is a rare congenital disorder that causes hyperammonaemic comas, resulting in severe neurological morbidity and usually leading to death during childhood. (2) Carglumic acid is the first drug to be used for replacement therapy. Data available in 2003 showed beneficial effects on growth and psychomotor development. (3) In 2007, about 20 patients treated with carglumic acid for N-acetyglutamate synthase deficiency, for at least 5 years in half of cases, were all still alive. Their development was normal when treatment was initiated before complications occurred. (4) No serious adverse effects have been observed. (5) In practice, although this treatment has to continue for life, carglumic acid represents a major advance for patients with N-acetylglutamate synthase deficiency.
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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] [What about the content of this article? (0)] [Affiliation(s)] [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.
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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
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Hwu WL, Chien YH, Tang NLS, Law LK, Lin CY, Lee NC. Deficiency of the carnitine transporter (OCTN2) with partial N-acetylglutamate synthase (NAGS) deficiency. J Inherit Metab Dis 2007; 30:816. [PMID: 17703373 DOI: 10.1007/s10545-007-0594-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2007] [Revised: 07/06/2007] [Accepted: 07/09/2007] [Indexed: 10/22/2022]
Abstract
A patient with recurrent episodes of hyperammonaemia (highest ammonia level recorded 229 micromol/L, normal 9-33) leading to altered levels of consciousness was diagnosed with partial N-acetylglutamate synthase (NAGS) deficiency (9% residual activity) at age 5 years and was treated with ammonia-conjugating agents (Ucephan 250 mg/kg per day and later sodium phenylbutyrate 200-250 mg/kg per day) for 15 years. A chronically low serum carnitine level (pretreatment plasma free carnitine 4 nmol/L, normal 37 +/- 8 nmol/L; total carnitine 8 nmol/L, normal 46 +/- 10) was assumed to be secondary and was treated with supplemental carnitine (30-50 mg/kg per day). Hypoglycaemia (blood sugar 35 mg/dl, normal 70-100), cardiomegaly, and fatty liver were also noted at diagnosis. The patient died unexpectedly at age 20 years. In retrospect, it was learned that the patient had stopped his carnitine without medical consultation several weeks prior to his death. Additional molecular investigations identified two mutations (R254X and IVS3 + 1G > A) in the patient's OCTN2 (SLC22A5) gene, consistent with a diagnosis of primary carnitine deficiency due to carnitine transporter defect. R245X is a founder mutation in Southern Chinese populations. It is unknown whether the original NAGS deficiency was primary or secondary, but molecular analysis of the NAGS gene failed to identify mutations. Urea cycle enzyme expression may be affected by fatty acid suppression of an AP-1 binding site in the promoter enhancer region of the urea cycle gene. Regardless, it is clear that the NAGS abnormality has led to delay of recognition of the OCTN2 defect, and modified the clinical course in this patient.
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Affiliation(s)
- W-L Hwu
- Department of Pediatrics and Medical Genetics, National Taiwan University Hospital and National Taiwan University College of Medicine, 7 Chung-Shan South Road, Taipei, 100, Taiwan.
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Nordenström A, Halldin M, Hallberg B, Alm J. A trial with N-carbamylglutamate may not detect all patients with NAGS deficiency and neonatal onset. J Inherit Metab Dis 2007; 30:400. [PMID: 17510757 DOI: 10.1007/s10545-007-0454-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2006] [Revised: 03/27/2007] [Accepted: 03/28/2007] [Indexed: 11/25/2022]
Abstract
N-acetylglutamate synthase (NAGS) deficiency is a rare urea cycle disorder. An effective treatment, N-carbamoyl-L-glutamic acid (NCGA), is now available, increasing the importance of identifying and treating these patients early. We describe a case with genetically verified NAGS deficiency and neonatal onset of severe hyperammonaemia. The ammonia levels increased above 1400 micromol/L. The patient did not respond to NCGA treatment during the first 15 h, indicating that a delayed response or no response cannot be used as a safe indicator for excluding NAGS deficiency in the acute situation. Hence, conventional treatment should not be delayed by a diagnostic procedure, such as a loading test. Furthermore, at 3 years of age this patient has normal psychomotor development, underlining the possibility of a favourable outcome despite markedly elevated ammonia levels, coma, and seizures in the neonatal period. Including NCGA early in the treatment of patients with hyperammonaemia may be of clinical importance. In order to detect patients with NAGS deficiency and neonatal onset and to optimize care, it is important to use the available treatment strategies to reduce plasma ammonia concentrations without delay. We propose the use of combined symptomatic treatment, i.e. glucose infusion, sodium benzoate, arginine or citrulline, and when indicated haemodialysis, as well as NCGA treatment in all neonates presenting with severe hyperammonaemia. The treatment should be continued until laboratory investigations are complete or indicate another disorder.
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Affiliation(s)
- A Nordenström
- Karolinska Institutet, Department of Pediatrics and PKU-Laboratory, Karolinska University Hospital, Huddinge, Sweden.
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Caldovic L, Morizono H, Panglao MG, Lopez GY, Shi D, Summar ML, Tuchman M. Late onset N-acetylglutamate synthase deficiency caused by hypomorphic alleles. Hum Mutat 2005; 25:293-8. [PMID: 15714518 DOI: 10.1002/humu.20146] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
N-acetylglutamate (NAG) is a unique cofactor that is essential for the conversion of ammonia to urea in the liver. N-acetylglutamate synthase (NAGS) catalyzes the formation of NAG. Deficiency of NAGS causes a block in ureagenesis resulting in hyperammonemia. Although a number of mutations have been identified in the NAGS gene, their effects on NAGS enzymatic activity have not been examined. We describe here three mutations in two families with NAGS deficiency. Studies of the purified recombinant mutant proteins revealed deleterious effects on NAGS affinity for substrates, and on the rate of catalysis. These studies provide a better understanding of the function of NAGS, and the mechanisms for deleterious effect of mutations causing inherited NAGS deficiency.
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Affiliation(s)
- Ljubica Caldovic
- Children's Research Institute, Children's National Medical Center, The George Washington University, Washington, DC 20010, USA
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