Conditions Carbamoyl Phosphate Synthetase I Deficiency

Carbamoyl phosphate synthetase I deficiency (CPS) is an inherited condition in which the body is unable to process and remove the waste, ammonia. CPS is considered an amino acid condition because ammonia is produced when the body breaks down proteins in food into their basic building blocks (amino acids). When the body’s process for removing waste is disrupted, dangerous amounts of ammonia begin to build up in the blood. If left untreated, this can result in developmental delay, intellectual disabilities, or even death. For the best possible outcome, it is important to identify CPS through newborn screening and begin proper treatment early.

Condition Type

Amino Acid Disorders


Carbamoyl phosphate synthetase I deficiency (CPS) is estimated to affect one out of every 100,000 to 800,000 babies born worldwide.

Also known as

  • CPS
  • Carbamoyltransferase deficiency
  • Hyperammonemia due to carbamoylphosphate synthetase deficiency
  • Carbamyl phosphate synthetase deficiency

Follow-Up Testing

Your baby’s doctor may ask you if your baby is showing any of the signs of CPS (see Early Signs below). If your baby has certain signs, your baby’s doctor may suggest starting immediate treatment.

If your baby’s newborn screening result for carbamoyl phosphate synthetase I deficiency (CPS) was out of the normal range, your baby’s doctor or the state screening program will contact you to arrange for your child to have additional testing. It is important to remember that an out-of-range screening result does not necessarily mean that your child has the condition. An out-of-range result may occur because the initial blood sample was too small or the test was performed too early. However, as a few babies do have the condition, it is very important that you go to your follow-up appointment for a confirmatory test. Because the harmful effects of untreated CPS can occur soon after birth, follow-up testing must be completed as soon as possible to determine whether or not your baby has the condition.

Follow-up testing will involve checking your baby’s urine and blood samples for harmful amounts of acids and toxins. Certain acids and toxins build up in the body when a child has an amino acid condition, so measuring the amounts of these substances in your baby’s body can help doctors determine if your baby has a condition. Normal levels of orotic acid in the urine and high levels of ammonia and certain amino acids in the blood may indicate that your baby has CPS. If blood and urine tests are uninformative, your baby’s doctor may need to evaluate a small sample of your baby’s liver.

About Carbamoyl Phosphate Synthetase I Deficiency

Early Signs

There are two main forms of carbomoyl phosphate synthetase I deficiency (CPS), which differ in the age of onset. In the first and most common form of CPS, signs usually begin shortly after birth. In the second form, signs of CPS might not become apparent until childhood or even adulthood. In these cases, the signs are usually less severe.

Early signs of CPS in babies include:

  • Poor appetite
  • Tiredness
  • Vomiting
  • Trouble regulating body temperature (your baby may get cold easily)
  • Trouble breathing
  • Seizures (also called epilepsy)
  • Uncontrolled body movements
  • Delayed growth

Many of these signs may occur when your baby eats foods that their body cannot break down. They can be triggered by long periods of time without eating, illnesses, and infections.

If your baby shows any of these signs, be sure to contact your baby’s health care provider immediately.


Dietary Treatments

Your baby may need to follow a low-protein diet to avoid certain foods that they cannot break down. A dietician or nutritionist can help you plan the appropriate diet for your child’s healthy growth.

Your baby’s doctor may recommend special foods or formulas for children with carbamoyl phosphate synthetase I deficiency (CPS). These formulas will likely need to continue through adulthood.

Supplements and Medications

Your baby’s health care provider may prescribe medications to help your baby’s body get rid of excess ammonia.

Expected Outcomes

Early diagnosis and proper treatment may prevent or delay the serious signs and symptoms of CPS in some children. This is why newborn screening for CPS is so important.

Even with treatment, some children may experience learning disabilities, intellectual disabilities, or tight muscles (spasticity), which are commonly associated with CPS.

Children who do not receive treatment for CPS are at risk for seizures, brain damage, coma, or even death.


When we eat food, our bodies break down proteins into a form that can be used by our cells. During this process, a waste product, called ammonia, is produced. Ammonia is processed and removed from the body through the action of several different enzymes. In carbamoyl phosphate synthetase I deficiency, the enzyme carbamoyl phosphate synthetase (CPS) is not working correctly.

CPS’s job is to help change ammonia into a form that can be removed from the body through urine. Babies with carbamoyl phosphate synthetase I deficiency (CPS) either do not make enough or make non-working CPS. When CPS does not work correctly, the body cannot get rid of ammonia properly. This causes high levels of ammonia to build up in the blood, which can be dangerous.

CPS is an autosomal recessive genetic condition. This means that a child must inherit two copies of the non-working gene for CPS, one from each parent, in order to have the condition. The parents of a child with an autosomal recessive condition each carry one copy of the non-working gene, but they typically do not show signs and symptoms of the condition. While having a child with CPS is rare, when both parents are carriers, they can have more than one child with the condition. Learn more about autosomal recessive inheritance.

Support for Carbamoyl Phosphate Synthetase I Deficiency

Support Services

Support groups can help connect families who have a child or other family member affected with CPS with a supportive community of people who have experience and expertise in living with the condition. These organizations offer resources for families, affected individuals, health care providers, and advocates.

Accessing Care

Work with your baby’s health care provider to determine the next steps for your baby’s care. Your baby’s doctor may help you coordinate care with a physician that specializes in metabolism, a dietician who can help plan your child’s specialized diet, and other medical resources in your community. Some children with CPS have developmental delays. If you think that your baby is not meeting their developmental milestones, ask your baby’s doctor about the next steps in accessing a developmental evaluation and care.

Because CPS is a genetic condition, you may want to talk with a genetics specialist. A genetic counselor or geneticist can help you understand the causes of the condition, discuss genetic testing for CPS, and understand what this diagnosis means for other family members and future pregnancies. Speak with your baby’s doctor about getting a referral. The Clinic Services Search Engine offered by the American College of Medical Genetics and Genomics (ACMG) and the Find a Genetic Counselor tool on the National Society of Genetic Counselors (NSGC) website are two good resources for you or your baby's health care provider to use to identify local specialists.

Families' Experiences

At this time we have not located a family story for this particular condition. If your family is affected by CPS and you would like to share your story, please contact us so other families may learn from your experience.

References & Sources

Visit MedlinePlus Genetics for more condition information

Visit OMIM to search its online catalog of human genes and disorders

Visit MedlinePlus for information on hereditary urea cycle abnormality

Visit GeneReviews for more information on urea cycle disorders

ACT Sheets

Healthcare professionals can learn more about confirmatory testing by reading the American College of Medical Genetics and Genomics' Algorithm for Diagnosis and ACT Sheet, a guide for follow-up after newborn screening. You can visit this page of the ACMG website here.

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