General Information for Families
A urea cycle disorder is a genetic disorder caused by a deficiency of one of the
enzymes in the urea cycle, which is responsible for removing ammonia from the blood
stream. The urea cycle involves a series of biochemical steps in which nitrogen,
a waste product of protein metabolism, is removed from the blood and converted to
urea. Normally, the urea is transferred into the urine and removed from the body.
In urea cycle disorders, the nitrogen accumulates in the form of ammonia, a highly
toxic substance, and is not removed from the body. Ammonia then reaches the brain
through the blood, where it causes irreversible brain damage and/or death.
Urea cycle disorders are included in the category of inborn errors of metabolism.
There is no cure. Inborn errors of metabolism are generally considered to be rare
but represent a substantial cause of brain damage and death among newborns and infants.
Because many cases of urea cycle disorders remain undiagnosed and/or infants born with the disorders die without a definitive diagnosis, the exact incidence of these
cases is unknown and underestimated. It is believed that up to 20% of Sudden Infant
Death Syndrome cases may be attributed to an undiagnosed inborn error of metabolism
such as urea cycle disorder.
There are six disorders of the urea cycle. Each is referred to by the initials of
the missing enzyme:
- CPS - Carbamyl Phosphate Synthetase
- NAGS- N-Acetylglutamate Synthetase
- OTC - Ornithine Transcarbamylase
- AS - Argininosuccinic Acid Synthetase (Citrullinemia)
- AL/ASA - Argininosuccinase Acid Lyase (Argininosuccinic Aciduria)
- AG - Arginase
Individuals with childhood or adult onset disease may have a partial enzyme deficiency. All of these disorders are transmitted genetically as autosomal recessive genes - each parent contributes a defective gene to the child, except for one of the defects, Ornithine Transcarbamylase Deficiency. This urea cycle disorder is acquired in one of three ways: as an X-linked trait from the mother, who may be an undiagnosed carrier; in some cases of female children, the disorder can also be inherited from the father's X-chromosome; and finally, OTC deficiency may be acquired as a "new" mutation occurring in the fetus uniquely.Recent research has shown that some female carriers of the disease may become symptomatic with the disorder later in life, suffering high ammonia levels. Several undiagnosed women have died during childbirth as a result of high ammonia levels and on autopsy were determined to have been unknown carriers of the disorder.
Source: National Urea Cycle Disorders Foundation
What are amino acid disorders?
Amino acid disorders (AA disorders) cause the body to have problems breaking down
certain proteins. The body breaks down, or metabolizes, food. The food is changed
into nutrients they body can use, and the body gets rid of the chemicals it does not need. Enzymes (chemicals that do jobs in the body) usually help break down food.
A person who has an AA disorder is missing a specific enzyme, or the enzyme is not working as well as it should. This prevents the body from breaking down protein
in food, and toxic chemicals build up in the body. The build up of toxic chemicals
can cause serious damage to organs. Each enzyme deficiency causes a different AA
disorder. A special diet and medication can prevent most problems.
What causes AA disorders?
AA disorders are inherited when both parents pass an abnormal AA gene to their child. This means both parents are carriers of a particular AA disorder. Carriers do not experience any health problems related to the AA disorder. When two carriers of a particular AA disorder have children together, there is a 1 in 4 (25%) chance for each baby to have the AA disorder.
How are AA disorders detected?
Newborn screening is done on tiny samples of blood taken from the infant’s heel 24-48 hours after birth. After a positive newborn screen, testing at special labs must be done to know for sure if a baby has an AA disorder.
What problems can AA disorders cause?
An AA disorder is different for each child. Untreated AA disorders can cause vomiting,
eye problems, liver problems, mental retardation, and possibly coma or death. It is extremely important to follow the doctor’s instructions about caring for a child with an AA disorder.
What is the treatment for AA disorders?
AA disorders can be treated. People with AA disorders should not eat certain proteins
that the body has trouble breaking down. Medication may help the body get rid of
harmful toxins. The treatment is life-long. For children who have an AA disorder:
- The child should have a primary care doctor, a pediatric metabolic specialist, and a dietician. These health professionals give the child good medical care and educate the family about the special diet.
- Families are taught to read labels carefully when shopping for food.
- Treatment for an AA disorder is lifelong, and a child with an AA disorder should see a doctor regularly.
Source: Minnesota Newborn Screening Program
National and State Specific Family Resources
View National and State Specific Family Resources
Urea Cycle Disorders Prevalence by State
The Region 4 Newborn Screening Data, summarized annually, provides detailed data on newborn screening results within Illinois, Indiana, Kentucky, Michigan, Minnesota, Ohio and Wisconsin. It is provided here to: assist families and physicians in knowing the relative number of confirmed annual cases for the disorder within each state and how it compares to other states in the region. assist families and specialists across states in connecting with specialists who may have experience treating a specific rare disorder. It is important to note that ongoing developments in the sophistication of technology allows states to progressively increase the number of disorders they screen in their program.
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