What Is Urea Cycle Disorder?

According to the National Urea Cycle Disorders Foundation (NUCDF), urea cycle disorders (UCD) are genetic disorders caused by deficiencies in one of the enzymes of the urea cycle--the metabolic process by which the body gets rid of nitrogen. Six enzymes take part in this process. When any of these enzymes are deficient, ammonia accumulates in the bloodstream. The increased levels of ammonia reach the brain and can cause irreversible brain damage, coma and/or death.

Significance

• Urea cycle disorders are categorized as inborn errors of metabolism which cause brain damage and death among newborns and infants. The NUCDF reports that an estimated 20 percent of Sudden Infant Death Syndrome cases may be attributed to an undiagnosed inborn error of metabolism such as a UCD.

Symptoms

• When an enzyme deficiency is severe, symptoms may be present at birth. Symptoms include irritability, refusal to feed, vomiting, lethargy, seizures, poor muscle tone, respiratory distress or coma. With limited or partial deficiencies, symptoms may not appear until childhood or adulthood and include failure to thrive, agitation, delirium, vomiting, slurred speech, unstable gait and unconsciousness.

Treatments

• Treatments consist of dietary management to limit ammonia production, in conjunction with medications and/or supplements to encourage the removal of ammonia from the bloodstream.

Considerations

• Because newborns are usually discharged from the hospital within 1 to 2 days after birth, the symptoms of a urea cycle disorder may not be recognized until the child is at home. In some instances the disorder may remain undiagnosed.

Warning

• Childhood episodes of UCD may be brought on by viral illnesses including chicken pox, colds or flu.