Definition of Hereditary urea cycle abnormality:

Hereditary urea cycle abnormality is an inherited condition that can cause problems with the removal of waste from the body in the urine.

Causes, incidence, and risk factors:

The urea cycle is a process in which waste (ammonia) is removed from the body. When you eat proteins, the body breaks them down into amino acids. Leftover amino acids turn into ammonia and must be removed from the body. The liver produces several chemicals (enzymes) that change ammonia into a form called urea, which the body can remove in the urine. If this process is disturbed, ammonia levels begin to rise.

Several inherited conditions can cause problems with this waste-removal process. People with a urea cycle disorder are missing a gene that makes the enzymes needed to break down ammonia in the body.

These diseases include:

• Argininosuccinic aciduria
• Arginase deficiency
• Carbamyl phosphate synthetase (CPS) deficiency
• Citrullinemia
• N-acetyl glutamate synthetase deficiency (NAGS)
• Ornithine transcarbamylase deficiency (OTC)

As a group, these disorders occur in 1 in 30,000 newborns. Ornithine transcarbamylase deficiency is the most common of these disorders.

Boys are more often affected by ornithine transcarbamylase deficiency than are girls. Girls are rarely affected, and those who are have milder symptoms and the disease begins later in life.

To get the other types of disorders, you need to get abnormal copies of the gene from both parents. Sometimes parents don't know they carry the gene until their child gets the disorder.