Information about Hyperammonemia

Classification & external resources

Ammonia
ICD-10	E72.2
ICD-9	270.6
DiseasesDB	20468
eMedicine	neuro/162  ped/1057
MeSH	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).

Specific types

In all cases Hyperammonemia results from defects of the Urea cycle. The following list includes such examples:

• Mendelian Inheritance in Man (OMIM) 311250 - hyperammonemia due to ornithine transcarbamylase deficiency
• Mendelian Inheritance in Man (OMIM) 606762 - hyperinsulinism-hyperammonemia syndrome (glutamate dehydrogenase 1)
• Mendelian Inheritance in Man (OMIM) 238970 - hyperornithinemia-hyperammonemia-homocitrullinuria syndrome (ornithine translocase)
• Mendelian Inheritance in Man (OMIM) 237310 - hyperammonemia due to N-acetylglutamate synthetase deficiency
• Mendelian Inheritance in Man (OMIM) 237300 - hyperammonemia due to carbamoyl phosphate synthetase i deficiency (carbamoyl phosphate synthase I)
• Mendelian Inheritance in Man (OMIM) 238750 - hyperlysinuria with hyperammonemia (genetics unknown)

Sequelae

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

See also

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

External links

• Organic Acidemia Association

•  • [ e] Metabolic pathology (, )
Amino acid	Aromatic (Phenylketonuria, Alkaptonuria, Ochronosis, Tyrosinemia, Albinism, Histidinemia) - Branched chain (Maple syrup urine disease, Propionic acidemia, Methylmalonic acidemia, Isovaleric acidemia, 3-Methylcrotonyl-CoA carboxylase deficiency) - Transport (Cystinuria, Cystinosis, Hartnup disease, Fanconi syndrome) - Sulfur (Homocystinuria, Cystathioninuria) - Urea cycle disorder (N-Acetylglutamate synthase deficiency, Carbamoyl phosphate synthetase I deficiency, Ornithine transcarbamylase deficiency, Citrullinemia, Argininosuccinic aciduria, Hyperammonemia) - Glutaric acidemia type 1 - Sarcosinemia
Carbohydrate	Lactose intolerance - Glycogen storage disease (type I, type II, type III, type IV, type V, type VI, type VII) - fructose metabolism (Fructose intolerance, Fructose bisphosphatase deficiency, Essential fructosuria) - galactose metabolism (Galactosemia, Galactose-1-phosphate uridylyltransferase galactosemia, Galactokinase deficiency) - other intestinal carbohydrate absorption (Glucose-galactose malabsorption, Sucrose intolerance) - pyruvate metabolism and gluconeogenesis (PCD, PDHA) - Pentosuria - Renal glycosuria
Lipid storage	Sphingolipidoses/Gangliosidoses: GM2 gangliosidoses (Sandhoff disease, Tay-Sachs disease) - GM1 gangliosidoses - Mucolipidosis type IV - Gaucher's disease - Niemann-Pick disease - Farber disease - Fabry's disease - Metachromatic leukodystrophy - Krabbe disease Neuronal ceroid lipofuscinosis (Batten disease) - Cerebrotendineous xanthomatosis - Cholesteryl ester storage disease (Wolman disease)
Other lipid	Lipoprotein/lipidemias: Hyperlipidemia - Hypercholesterolemia - Familial hypercholesterolemia - Xanthoma - Combined hyperlipidemia - Lecithin cholesterol acyltransferase deficiency - Tangier disease - Abetalipoproteinemia Fatty acid: Adrenoleukodystrophy - Carnitine (Primary, I, II)
Mineral	Cu Wilson's disease/Menkes disease - Fe Haemochromatosis - Zn Acrodermatitis enteropathica - PO43− Hypophosphatemia/Hypophosphatasia - Mg2+ Hypermagnesemia/Hypomagnesemia - Ca2+ Hypercalcaemia/Hypocalcaemia/Disorders of calcium metabolism
Fluid, electrolyte and acid-base balance	Electrolyte disturbance - Na+ Hypernatremia/Hyponatremia - Acidosis (Metabolic, Respiratory, Lactic) - Alkalosis (Metabolic, Respiratory) - Mixed disorder of acid-base balance - H2O Dehydration/Hypervolemia - K+ Hypokalemia/Hyperkalemia - Cl− Hyperchloremia/Hypochloremia
Purine and pyrimidine	Hyperuricemia - Lesch-Nyhan syndrome - Xanthinuria
Porphyrin	Acute intermittent, Gunther's, Cutanea tarda, Erythropoietic, Hepatoerythropoietic, Hereditary copro-, Variegate
Bilirubin	Unconjugated (Gilbert's syndrome, Crigler-Najjar syndrome) - Conjugated (Dubin-Johnson syndrome, Rotor syndrome)
Glycosaminoglycan	Mucopolysaccharidosis - 1:Hurler/Hunter - 3:Sanfilippo - 4:Morquio - 6:Maroteaux-Lamy - 7:Sly
Glycoprotein	Mucolipidosis - I-cell disease - Pseudo-Hurler polydystrophy - Aspartylglucosaminuria - Fucosidosis - Alpha-mannosidosis - Sialidosis
Other	Alpha 1-antitrypsin deficiency - Cystic fibrosis - Amyloidosis (Familial Mediterranean fever) - Acatalasia