Hyperammonemia

Hyperammonemia 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. more...

Ammonia is a substance that contains nitrogen. It is a product of the catabolism of protein. It is converted to the non-toxic substance urea prior to excretion in urine by the kidneys. The metabolic pathways that synthesise urea are located in mitochondria. 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

• OMIM 311250 - hyperammonemia due to ornithine transcarbamylase deficiency
• OMIM 606762 - hyperinsulinism-hyperammonemia syndrome
• OMIM 238970 - hyperornithinemia-hyperammonemia-homocitrullinuria syndrome
• OMIM 237310 - hyperammonemia due to n-acetylglutamate synthetase deficiency
• OMIM 237300 - hyperammonemia due to carbamoyl phosphate synthetase i deficiency
• OMIM 238750 - hyperlysinuria with hyperammonemia

Sequelae

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

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