The liver makes urea from nitrogen waste, which is then excreted in the urine. Several hereditary conditions can cause this problem. These are genetic diseases caused by a the lack of a gene to make 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)

Causes and Risks

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

Ornithine transcarbamylase deficiency is an X-linked recessive disorder (which will occur in all males who inherit the gene because they lack another X which could make up for it).  Females are rarely affected -- 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, they can appear in families which had no prior knowledge that parents were carriers. 

As a result of these disorders, ammonia levels rise as proteins aren't 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.

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

Ency. home > Disease > H > Hereditary urea cycle abnormality

[an error occurred while processing this directive]