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Hereditary urea cycle abnormality

• Overview
• Symptoms
• Treatment
• Prevention

Definition:

The urea cycle is a metabolic process in which waste (nitrogen) from the breakdown of dietary proteins is incorporated by the liver into a form (called urea) that can be excreted from the body in the urine.

Several hereditary conditions can cause problems with this waste-removal process. These are genetic diseases caused by the lack of a gene that makes critical enzymes needed for the urea cycle. They include:

• ornithine transcarbamylase deficiency (OTC)
• citrullinemia
• arginase deficiency
• argininosuccinic aciduria
• carbamyl phosphate synthetase (CPS) deficiency
• N-acetyl glutamate synthetase deficiency (NAGS)

Alternative Names:

Abnormality of the urea cycle - hereditary; Urea cycle - hereditary abnormality

Causes, incidence, and risk factors:

As a group, these disorders occur in 1 in 30,000 newborns. All are genetic diseases associated with lack of a protein/enzyme activity in the urea cycle. Ornithine transcarbamylase deficiency is the most common.

Ornithine transcarbamylase deficiency is an X-linked recessive disorder (which means that all boys who inherit one bad copy of the gene will have the disease). Girls are rarely affected, and those who are have milder symptoms and later onset.

The other types are inherited in an autosomal recessive manner, meaning that you need to get bad copies of the gene from both parents to develop the condition. Thus, the disorders can appear in families with no prior knowledge that the parents were carriers.

As a result of these disorders, ammonia levels rise as proteins are not properly broken down into urea and removed. If ammonia rises too high in the body it can cause symptoms, such as confusion. Untreated, this can progress to swelling of the brain, coma, and death.

These disorders are frequently diagnosed in infancy. Typically, the baby begins nursing well and seems normal. However, with time there is progressively poorer feeding, vomiting, and sleepiness which may be so deep that the baby is difficult to arouse.

• Review Date: 3/13/2006
• Reviewed By: Lamya Alarif, Ph.D., H.C.L.D., Immunology and Genetics Associates, McLean, VA. Review provided by VeriMed Healthcare Network.

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