N-Acetylglutamate Synthetase Deficiency Treatment & Management

  • Author: Karl S Roth, MD; Chief Editor: Bruce Buehler, MD   more...
 
Updated: Mar 19, 2010
 

Medical Care

  • Immediate cessation of protein intake is mandatory in the face of high blood ammonia levels with provision of supplementary nonprotein energy to close the caloric gap. In most cases of severe hyperammonemia, the patient is given nothing enterally until the hyperammonemia is well controlled.
  • Treatment of severe hyperammonemia is a true emergency.
    • Reduction of blood ammonia can usually be achieved with intravenous sodium benzoate and phenylacetate. Intravenous sodium benzoate and phenylacetate (Ammonul) was approved in the United States in February, 2005.
    • Alternatively, hemodialysis is usually effective in bringing down the ammonia level, especially with the initial presentation.
    • Exchange transfusion is ineffective and is not generally recommended.
    • Intravenous fluids with glucose and sometimes arginine hydrochloride (HCl) added may be indicated.[3]
    • Maintaining as high of an energy intake as possible is important.
  • Specific therapy of N- acetylglutamate synthetase (NAGS) deficiency following diagnosis depends on dietary protein restriction and provision of arginine to enhance availability of ornithine and administration of carbamylglutamate (which is not widely available), a functional analogue of NAG. Some patients have done well using this regimen. Whether or not oral sodium phenylbutyrate is helpful in this condition is unclear.
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Consultations

  • NAGS deficiency is an extremely rare disorder with complex treatment.
  • Consultation with a metabolic disease/medical genetic specialist is usually necessary for assistance with laboratory diagnosis and clinical care. Contact these consultants by telephone if they are not locally available.
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Diet

  • A low-protein diet is generally recommended with dietary supervision under the direction of a dietitian experienced in the care of patients with metabolic disease.
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Contributor Information and Disclosures
Author

Karl S Roth, MD  Professor and Chair, Department of Pediatrics, Creighton University School of Medicine

Karl S Roth, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American College of Nutrition, American Pediatric Society, American Society for Clinical Nutrition, American Society of Nephrology, Association of American Medical Colleges, Medical Society of Virginia, New York Academy of Sciences, Sigma Xi, Society for Pediatric Research, and Southern Society for Pediatric Research

Disclosure: Nothing to disclose.

Specialty Editor Board

Uri S Alon, MD  Director of Bone and Mineral Disorders Clinic and Renal Research Laboratory, Children's Mercy Hospital of Kansas City; Professor, Department of Pediatrics, Division of Pediatric Nephrology, University of Missouri-Kansas City School of Medicine

Uri S Alon, MD is a member of the following medical societies: American Federation for Medical Research

Disclosure: Nothing to disclose.

Mary L Windle, PharmD  Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Pharmacy Editor, eMedicine

Disclosure: Nothing to disclose.

Robert Anthony Saul, MD  Clinical Professor, Department of Pediatrics, University of South Carolina; Senior Clinical Geneticist, Greenwood Genetic Center

Robert Anthony Saul, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Medical Genetics, and American College of Physician Executives

Disclosure: Nothing to disclose.

Paul D Petry, DO, FACOP, FAAP  Consulting Staff, Freeman Pediatric Care, Freeman Health System

Paul D Petry, DO, FACOP, FAAP is a member of the following medical societies: American Academy of Osteopathy, American Academy of Pediatrics, American College of Osteopathic Pediatricians, and American Osteopathic Association

Disclosure: Nothing to disclose.

Chief Editor

Bruce Buehler, MD  Professor, Department of Pediatrics and Genetics, Director RSA, University of Nebraska Medical Center

Bruce Buehler, MD is a member of the following medical societies: American Academy for Cerebral Palsy and Developmental Medicine, American Academy of Pediatrics, American Association on Mental Retardation, American College of Medical Genetics, American College of Physician Executives, American Medical Association, and Nebraska Medical Association

Disclosure: Nothing to disclose.

References

  1. Tuchman M, Lee B, Lichter-Konecki U, et al. Cross-sectional multicenter study of patients with urea cycle disorders in the United States. Mol Genet Metab. Aug 2008;94(4):397-402. [Medline].

  2. Caldovic L, Morizono H, Tuchman M. Mutations and polymorphisms in the human N-acetylglutamate synthase (NAGS) gene. Hum Mutat. Aug 2007;28(8):754-9. [Medline].

  3. Gessler P, Buchal P, Schwenk HU, Wermuth B. Favourable long-term outcome after immediate treatment of neonatal hyperammonemia due to N-acetylglutamate synthase deficiency. Eur J Pediatr. Feb 2010;169(2):197-9. [Medline].

  4. Tuchman M, Caldovic L, Daikhin Y, et al. N-carbamylglutamate markedly enhances ureagenesis in N-acetylglutamate deficiency and propionic acidemia as measured by isotopic incorporation and blood biomarkers. Pediatr Res. Aug 2008;64(2):213-7. [Medline].

  5. Bachmann C, Colombo JP, Jaggi K. N-acetylglutamate synthetase (NAGS) deficiency: diagnosis, clinical observations and treatment. Adv Exp Med Biol. 1982;153:39-45. [Medline].

  6. Caldovic L, Morizono H, Panglao MG, et al. Late onset N-acetylglutamate synthase deficiency caused by hypomorphic alleles. Hum Mutat. Mar 2005;25(3):293-8. [Medline].

  7. Caldovic L, Morizono H, Panglao MG, et al. Null mutations in the N-acetylglutamate synthase gene associated with acute neonatal disease and hyperammonemia. Hum Genet. Apr 2003;112(4):364-8. [Medline].

  8. Elpeleg O, Shaag A, Ben-Shalom E, Schmid T, Bachmann C. N-acetylglutamate synthase deficiency and the treatment of hyperammonemic encephalopathy. Ann Neurol. Dec 2002;52(6):845-9. [Medline].

  9. Elpeleg ON, Colombo JP, Amir N, et al. Late-onset form of partial N-acetylglutamate synthetase deficiency. Eur J Pediatr. Jun 1990;149(9):634-6. [Medline].

  10. Guffon N, Schiff M, Cheillan D, et al. Neonatal hyperammonemia: the N-carbamoyl-L-glutamic acid test. J Pediatr. Aug 2005;147(2):260-2. [Medline].

  11. Guffon N, Vianey-Saban C, Bourgeois J, et al. A new neonatal case of N-acetylglutamate synthase deficiency treated by carbamylglutamate. J Inherit Metab Dis. 1995;18(1):61-5. [Medline].

  12. Haberle J, Koch HG. Genetic approach to prenatal diagnosis in urea cycle defects. Prenat Diagn. May 2004;24(5):378-83. [Medline].

  13. Plecko B, Erwa W, Wermuth B. Partial N-acetylglutamate synthetase deficiency in a 13-year-old girl: diagnosis and response to treatment with N-carbamylglutamate. Eur J Pediatr. Dec 1998;157(12):996-8. [Medline].

 
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Compounds comprising the urea cycle are numbered sequentially, beginning with carbamyl phosphate (1). At this step, the first waste nitrogen is incorporated into the cycle; at this step, N-acetylglutamate exerts its regulatory control on the mediating enzyme, carbamyl phosphate synthetase (CPS). Compound 2 is citrulline, the product of condensation between carbamyl phosphate (1) and ornithine (8); the mediating enzyme is ornithine transcarbamylase. Compound 3 is aspartic acid, which is combined with citrulline to form argininosuccinic acid (ASA) (4); the reaction is mediated by ASA synthetase. Compound 5 is fumaric acid generated in the reaction that converts ASA to arginine (6), which is mediated by ASA lyase.
 
 
 
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