eMedicine Specialties > Pediatrics: Genetics and Metabolic Disease > Metabolic Diseases

N-Acetylglutamate Synthetase Deficiency: Differential Diagnoses & Workup

Author: Karl S Roth, MD, Professor and Chair, Department of Pediatrics, Creighton University School of Medicine
Contributor Information and Disclosures

Updated: Aug 4, 2008

Differential Diagnoses

Arginase Deficiency
Hyperammonemia-Hyperornithinemia-Homocitrullinemia Syndrome
Argininosuccinate Lyase Deficiency
Ornithine Transcarbamylase Deficiency
Carbamoyl Phosphate Synthetase Deficiency
Citrullinemia
Hyperammonemia

Other Problems to Be Considered

Lysinuric protein intolerance
Reye syndrome

Workup

Laboratory Studies

  • Affected newborns may experience fulminant hyperammonemia, which remains undetected unless index of suspicion is high.
  • No routine laboratory tests provide definitive clues.
    • The BUN level may be low, but this is an unreliable index of high blood ammonia.
    • A respiratory alkalosis may be present.
    • Urine orotic acid levels are within reference ranges.
  • Plasma alanine and glutamine levels are elevated.
  • Urine amino acids are nondiagnostic in N- acetylglutamate synthetase (NAGS) deficiency but are important in order to help rule out hyperammonemia-hyperornithinemia-homocitrullinemia (HHH) or lysinuric protein intolerance (LPI) (see Differentials).
  • Urine organic acids are within reference ranges in NAGS deficiency. Ruling out organic acid disorders, which can present with similar signs and symptoms and hyperammonemia, is important.

Imaging Studies

  • Imaging studies generally are not helpful, with the exception of brain imaging when cerebral edema is suspected. Documenting a finding of cerebral edema is important.

Procedures

  • A liver biopsy, best performed when the patient is stable, is essential for definitive diagnosis.
  • As a mitochondrial enzyme, it is quite labile; therefore, handle the specimen with scrupulous care and identify a laboratory that is capable of performing the enzymatic testing prior to scheduling the biopsy.

More on N-Acetylglutamate Synthetase Deficiency

Overview: N-Acetylglutamate Synthetase Deficiency
Differential Diagnoses & Workup: N-Acetylglutamate Synthetase Deficiency
Treatment & Medication: N-Acetylglutamate Synthetase Deficiency
Follow-up: N-Acetylglutamate Synthetase Deficiency
Multimedia: N-Acetylglutamate Synthetase Deficiency
References

References

  1. 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].

  2. 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].

  3. 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].

  4. 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].

  5. 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].

  6. 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].

  7. 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].

  8. 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].

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

  10. 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].

Further Reading

Keywords

N -acetylglutamate synthetase deficiency, NAGS, NAGS deficiency, acetyl-coenzyme A, acetyl-CoA, carbamyl phosphate synthetase, CPS, hyperammonemia, urea cycle defect, anorexia, coma, apnea, respiratory failure, seizures, dysdiadochokinesia, hypothermia, respiratory alkalosis, arginase deficiency, hyperammonemia-hyperornithinemia-homocitrullinemia syndrome

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.

Medical Editor

Uri S Alon, MD, Director of Research and Education, Department of Pediatrics, Division of Pediatric Nephrology, Children's Mercy Hospital of Kansas City; Professor, University of Missouri at Kansas City
Uri S Alon, MD is a member of the following medical societies: American Federation for Medical Research
Disclosure: Nothing to disclose.

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc
Disclosure: Pfizer Inc Stock Investment from broker recommendation; Avanir Pharma Stock Investment from broker recommendation

Managing Editor

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.

CME Editor

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, Pathology and Microbiology, Executive Director, Hattie B Munroe Center for Human Genetics and Rehabilitation, 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.

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