General Condition Information
- Carbamoyl phosphate synthetase deficiency
- Carbamoylphosphate synthetase deficiency
- Carbamoyltransferase deficiency, carbamoyl phosphate synthetase I deficiency
- It is unknown how many babies are born with this rare condition each year in the United States.
- Visit GeneReviews to learn more about how often this condition occurs.
What is Carbamoyl Phosphate Synthetase I Deficiency
Carbamoyl phosphate synthetase I (CPS I) deficiency is an inherited (genetic) condition that prevents the body from removing ammonia properly. Ammonia is a waste product produced when the body breaks down protein.
CPS I is an enzyme that helps your body break down proteins. You need CPS I enzyme for a process called the urea cycle. The urea cycle helps remove ammonia from the body. The CPS I enzyme controls the first step in the urea cycle.
Without enough working CPS I enzyme, your baby has trouble breaking down proteins and getting rid of ammonia. High amounts of ammonia can damage your baby’s brain and body. If untreated, this damage leads to the signs and symptoms of the condition.
Newborn Screening and Follow-Up
Newborn screening for CPS I deficiency requires collecting a small amount of blood from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.
Screening measures how much citrulline is in your baby’s blood. Citrulline is one of the products of the urea cycle and does not get formed when the CPS I enzyme is not working. Babies with very low levels of citrulline might have CPS I deficiency.
If your baby’s blood spot screening result for CPS I deficiency is out-of-range, your baby’s health care provider will contact you. Together, you will discuss next steps and follow-up plans.
An out-of-range screening result does not mean that your baby definitely has the condition. It does mean that your baby needs more follow-up testing. To learn more about screening results, visit the Blood Spot Screening Results page.
Your baby may need the following tests after an out-of-range screening result:
- Blood and/or urine tests
- Genetic testing using a blood sample
You should complete any recommended follow-up testing as soon as possible. Babies with this condition can have serious health problems soon after birth if they are not diagnosed and treated quickly.
False-positive newborn screening results for this condition can happen. Screening samples collected too early (before the baby is 24 hours of age) may cause false positive results. Babies with other conditions that have low citrulline levels may also be detected through this screening. An example of another condition that may be detected is ornithine translocase (OTC) deficiency.
Newborn screening helps babies lead healthier lives. If your baby has an out-of-range result, follow up with your health care provider quickly. It is important to follow their instructions. Your baby may need to get treatment right away, even if they are not showing signs or symptoms. In some cases, your baby’s health care provider may decide it is best to watch (monitor) your baby to decide next steps. Careful monitoring and early treatment will help your baby stay as healthy as possible.
Signs of CPS I deficiency can usually be seen within the first few days of life.
Signs of the condition may include the following:
A change in the CPS1 gene causes this condition. This gene gives the body instructions for making the enzyme CPS I. This enzyme helps remove ammonia from the body.
Without a working CPS1 gene, your baby’s body cannot make enough working enzyme. As a result, ammonia builds up. High levels of ammonia can cause brain damage.
- CPS I deficiency is an autosomal recessive condition. Babies inherit it when each parent passes down a nonworking CPS1 gene to their baby. Only babies with two nonworking CPS1 genes—one from the mom and one from the dad—have this condition.
- People with one working copy and one nonworking copy of the CPS1 gene are called carriers.
- Carriers do not have or develop the condition. However, they may pass down a nonworking copy of the gene to their children.
- If two parents are carriers of a nonworking copy of the CPS1 gene, they have a 1 in 4 chance of having a child with CPS I deficiency.
- Carriers for CPS I deficiency often do not know they are carriers before having a child with the condition. In most cases, families have no history of the condition until the birth of a child with CPS I deficiency.
- Parents who already have a child with CPS I deficiency still have a 1 in 4 chance of having another child with CPS I deficiency. This 1 in 4 chance stays the same for future children.
- Genetic counselors and medical geneticists can help families learn about this condition and the chance of having children with it. Visit the National Society of Genetic Counselors to find a genetic counselor and the American College of Medical Genetics and Genomics to find a medical geneticist.
Treatment and Management
It is important to talk to your health care provider about which treatment(s) are best for your baby. The goal of treatment is to prevent the health problems caused by this condition.
Treatments may include the following:
- Diet low in protein
- Special foods or formulas
- Arginine and citrulline supplements
- Liver transplant
Early and ongoing treatment can be lifesaving and can lead to better growth and development.