Hyperammonemia

Infobox_Disease
Name = PAGENAME


Caption = Ammonia
DiseasesDB = 20468
ICD10 = ICD10|E|72|2|e|70
ICD9 = ICD9|270.6
ICDO =
OMIM =
MedlinePlus =
eMedicineSubj = neuro
eMedicineTopic = 162
eMedicine_mult = eMedicine2|ped|1057 | MeshID = D022124

Hyperammonemia (or 'hyperammonaemia') is a metabolic disturbance characterised by an excess of ammonia in the blood. It is a dangerous condition that may lead to encephalopathy and death. It may be primary or secondary.

Ammonia is a substance that contains nitrogen. It is a product of the catabolism of protein. It is converted to the less toxic substance urea prior to excretion in urine by the kidneys. The metabolic pathways that synthesise urea are located first in the mitochondria and then into the cytosol. The process is known as the urea cycle, which comprises several enzymes acting in sequence.

Types

Primary vs. secondary

* Primary hyperammonemia is caused by several inborn errors of metabolism that are characterised by reduced activity of any of the enzymes in the urea cycle.
* Secondary hyperammonemia is caused by inborn errors of intermediary metabolism characterised by reduced activity in enzymes that are not part of the urea cycle (e.g .Propionic acidemia, Methylmalonic acidemia) or dysfunction of cells that make major contributions to metabolism (eg hepatic failure).

pecific types

The following list includes such examples:

* - hyperammonemia due to ornithine transcarbamylase deficiency
* - hyperinsulinism-hyperammonemia syndrome (glutamate dehydrogenase 1)
* - hyperornithinemia-hyperammonemia-homocitrullinuria syndrome (ornithine translocase)
* - hyperammonemia due to N-acetylglutamate synthetase deficiency
* - hyperammonemia due to carbamoyl phosphate synthetase I deficiency (carbamoyl phosphate synthetase I)
* - hyperlysinuria with hyperammonemia (genetics unknown)
* Methylmalonic acidemia
* Isovalemic acidemia
* Propionic acidemia

Treatment

Treatment centers on limiting intake of ammonia and increasing its excretion. Dietary protein (a source of ammonium) is restricted and caloric intake is provided by glucose and fat. Intravenous sodium phenylacetate and sodium benbenzoate are pharmacologic agents commonly used to treat hyperammonemia [ [http://www.emedicine.com/neuro/TOPIC162.HTM eMedicine - Hyperammonemia : Article by Kazi Imran Majeed ] ] . Sodium phenylacetate and sodium benzoate can serve as alternatives to urea for the excretion of waste nitrogen. Phenylacetate conjugates with glutamine to form phenylacetylglutamine, which is excreted by the kidneys. Similarly, sodium benzoate reduces ammonia content in the blood by conjugating with glycine to form hippuric acid, which is rapidly excreted by the kidneys [ [http://www.rxlist.com/cgi/generic/ammonul_cp.htm Ammonul (Sodium Phenylacetate and Sodium Benzoate Injection) clinical pharmacology - prescription drugs and medications at RxList ] ] . A preparation containing sodium phenylacetate and sodium benzoate is available under the trade name Ammonul.

equelae

Hyperammonemia is one of the metabolic derangements that contribute to hepatic encephalopathy.

ee also

* Citrullinemia
*N-acetylglutamate synthetase deficiency
*Ornithine translocase deficiency

References

External links

* [http://www.oaanews.org Organic Acidemia Association]
* [http://www.medscape.com/viewarticle/465899_8 Article on causes of hyperammonemia in the newborn.]