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FATIN SALINA ZAINAL ABIDIN

BMD103011

Hyperammonemia

Definition

-the presence of an excess of ammonia in the blood.

-genetic defects of urea cycle or liver disease.

Types of hyperammonemia :-

1. Acquired hyperammonemia-liver disease is common, may be due to viral hepatitis/ hepatotoxins

(alcohol)

-cirrhosis of liver -> formation of collateral circulation around

liverportal blood is shunted directly into systemic circulation and

does not have access to the liver. The conversion of ammonia to urea

is , therefore , severely impaired leading to elevated levels of

ammonemia.

2. congenital hyperammonemia

-ornithine transcarbamoylase deficiency ( X-linked) most common

affect male, female carrier. All of the other urea cycle disorders

follow an autosomal recessive inheritance pattern. It is due to failure

to synthesize urea leads to hyperammonemia during 1st week

following birth.

7/23/2019 Hyperammonemia.docx

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FATIN SALINA ZAINAL ABIDIN

BMD103011

Type I Hyperammonemia

Carbamoyl phosphate synthetase I (CPS I) deficiency:

This defect is inherited in an autosomal recessive pattern. The reaction takes place : hepatic mitochondria. Activity of the cycle is regulated by the rate of synthesis of N -

acetylglutamate, the enzyme activator of CPS I, which initiates

incorporation of ammonia into the cycle

In the presence of N acetylglutamate, ammonium ions combine withbicarbonate to form carbamoyl phosphate.

Lack of the enzyme CPS I prevents ammonia from being turned into ureaand being excreted in the urine.