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N-acetylglutamate synthase deficiency

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Description

N-acetylglutamate synthase deficiency is a disorder that causes abnormally high levels of ammonia to accumulate in the blood. Ammonia, which is formed when proteins are broken down in the body, is toxic if the levels become too high. The brain is especially sensitive to the effects of excess ammonia.

The signs and symptoms of N-acetylglutamate synthase deficiency often become evident in the first few days of life. An infant with this condition may be lacking in energy (lethargic) or unwilling to eat, and have difficulty controlling his or her breathing rate or body temperature. Severely affected babies may experience seizures or unusual body movements, or go into a coma. Complications of N-acetylglutamate synthase deficiency may include developmental delay and intellectual disability.

In some affected individuals, signs and symptoms of N-acetylglutamate synthase deficiency do not appear until later in life. Some people with this form of the disorder notice that eating high-protein foods, such as meat, affects how they feel, although they may not know why. In many affected adults, illness or other stress can trigger episodes of vomiting, lack of coordination, headaches, confusion, behavioral changes, or coma.

Frequency

N-acetylglutamate synthase deficiency is a very rare disorder. It is estimated to affect fewer than 1 in 2 million people worldwide.

Causes

Mutations in the NAGS gene cause N-acetylglutamate synthase deficiency. This condition belongs to a class of genetic diseases called urea cycle disorders because they are caused by problems with a process in the body called the urea cycle. The urea cycle is a sequence of reactions that occurs in liver cells. This cycle breaks down excess nitrogen, which is made when protein is used by the body, to make a compound called urea. Urea is removed from the body in urine.

The NAGS gene provides instructions for making the enzyme N-acetylglutamate synthase, which is integral to the first step of the urea cycle.

In people with N-acetylglutamate synthase deficiency, N-acetylglutamate synthase is not available in sufficient quantities, or is not present at all. As a result, the urea cycle is impaired, and nitrogen is not broken down efficiently. The excess nitrogen accumulates in the blood in the form of ammonia. This buildup of ammonia damages tissues in the brain and causes neurological problems and other signs and symptoms of N-acetylglutamate synthase deficiency.

Inheritance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Other Names for This Condition

  • hyperammonemia, type III
  • N-acetylglutamate synthetase deficiency
  • NAGS deficiency

Additional Information & Resources

Genetic and Rare Diseases Information Center

Patient Support and Advocacy Resources

Research Studies from ClinicalTrials.gov

Catalog of Genes and Diseases from OMIM

Scientific Articles on PubMed

References

  • Caldovic L, Morizono H, Panglao MG, Cheng SF, Packman S, Tuchman M. Null mutations in the N-acetylglutamate synthase gene associated with acute neonatal disease and hyperammonemia. Hum Genet. 2003 Apr;112(4):364-8. Epub 2003 Feb 20. Citation on PubMed
  • 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 Mar;25(3):293-8. Citation on PubMed
  • 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 Jan 24;19(2). pii: E345. doi: 10.3390/ijms19020345. Review. Citation on PubMed or Free article on PubMed Central
  • Elpeleg O, Shaag A, Ben-Shalom E, Schmid T, Bachmann C. N-acetylglutamate synthase deficiency and the treatment of hyperammonemic encephalopathy. Ann Neurol. 2002 Dec;52(6):845-9. Citation on PubMed
  • Häberle J, Schmidt E, Pauli S, Kreuder JG, Plecko B, Galler A, Wermuth B, Harms E, Koch HG. Mutation analysis in patients with N-acetylglutamate synthase deficiency. Hum Mutat. 2003 Jun;21(6):593-7. Citation on PubMed
  • 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 Jul;37(7):679-94. doi: 10.1002/humu.22995. Epub 2016 May 6. Citation on PubMed
  • Schmidt E, Nuoffer JM, Häberle J, Pauli S, Guffon N, Vianey-Saban C, Wermuth B, Koch HG. Identification of novel mutations of the human N-acetylglutamate synthase gene and their functional investigation by expression studies. Biochim Biophys Acta. 2005 Apr 15;1740(1):54-9. Epub 2005 Feb 24. Citation on PubMed
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